Flash memory

Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It is primarily used in memory cards, USB flash drives, MP3 players and solid-state drives for general storage and transfer of data between computers and other digital products(SONY VGP-BPS13Q Battery). It is a specific type of EEPROM (electrically erasable programmable read-only memory) that is erased and programmed in large blocks; in early flash the entire chip had to be erased at once(SONY VGP-BPS13B/Q Battery). Flash memory costs far less than byte-programmable EEPROM and therefore has become the dominant technology wherever a significant amount of non-volatile, solid state storage is needed(SONY VGN NR11S/S battery). Example applications include PDAs (personal digital assistants), laptop computers, digital audio players, digital cameras and mobile phones. It has also gained popularity in console video game hardware, where it is often used instead of EEPROMs or battery-powered static RAM (SRAM) for game save data(SONY VGN NR11M/S battery).

Flash memory is non-volatile, meaning no power is needed to maintain the information stored in the chip. In addition, flash memory offers fast read access times (although not as fast as volatile DRAM memory used for main memory in PCs) and better kinetic shock resistance than hard disks(SONY VGN NR11Z/S battery). These characteristics explain the popularity of flash memory in portable devices. Another feature of flash memory is that when packaged in a "memory card," it is extremely durable, being able to withstand intense pressure, extremes of temperature, and even immersion in water(SONY VGN NR11Z/T battery).

Although technically a type of EEPROM, the term "EEPROM" is generally used to refer specifically to non-flash EEPROM which is erasable in small blocks, typically bytes. Because erase cycles are slow(SONY VGP-BPS13A/Q Battery), the large block sizes used in flash memory erasing give it a significant speed advantage over old-style EEPROM when writing large amounts of data(SONY Vaio PCG-F305 battery).

History

Flash memory (both NOR and NAND types) was invented by Dr. Fujio Masuoka while working for Toshiba circa 1980. According to Toshiba, the name "flash" was suggested by Dr. Masuoka's colleague, Mr. Shoji Ariizumi(SONY VGP-BPS21/S Battery), because the erasure process of the memory contents reminded him of the flash of a camera. Dr. Masuoka presented the invention at the IEEE 1984 International Electron Devices Meeting (IEDM) held in San Francisco, California(SONY VGP-BPS21 Battery).

Intel Corporation saw the massive potential of the invention and introduced the first commercial NOR type flash chip in 1988. NOR-based flash has long erase and write times, but provides full address and data buses(SONY VGP-BPS21B Battery), allowing random access to any memory location. This makes it a suitable replacement for older read-only memory (ROM) chips, which are used to store program code that rarely needs to be updated, such as a computer's BIOS or the firmware of set-top boxes(SONY VGP-BPS21A/B Battery). Its endurance is 10,000 to 1,000,000 erase cycles. NOR-based flash was the basis of early flash-based removable media; CompactFlash was originally based on it, though later cards moved to less expensive NAND flash(SONY VAIO PCG-5K1L battery).

Toshiba announced NAND flash at the 1987 International Electron Devices Meeting. It has reduced erase and write times, and requires less chip area per cell, thus allowing greater storage density and lower cost per bit than NOR flash; it also has up to ten times the endurance of NOR flash(SONY VAIO PCG-6W2L battery). However, the I/O interface of NAND flash does not provide a random-access external address bus. Rather, data must be read on a block-wise basis, with typical block sizes of hundreds to thousands of bits. This made NAND flash unsuitable as a drop-in replacement for program ROM since most microprocessors and microcontrollers required byte-level random access(SONY VAIO PCG-7112L battery). In this regard NAND flash is similar to other secondary storage devices such as hard disks and optical media, and is thus very suitable for use in mass-storage devices such as memory cards(SONY VAIO PCG-8Z1L battery). The first NAND-based removable media format was SmartMedia in 1995, and many others have followed, including MultiMediaCard, Secure Digital, Memory Stick and xD-Picture Card. A new generation of memory card formats(SONY VAIO PCG-8Z2L battery), including RS-MMC, miniSD and microSD, and Intelligent Stick, feature extremely small form factors. For example, the microSD card has an area of just over 1.5 cm2, with a thickness of less than 1 mm. microSD capacities range from 64 MB to 32 GB, as of March 2010(SONY VAIO PCG-8Y2L battery).

Principles of operation

Flash memory stores information in an array of memory cells made from floating-gate transistors. In traditional single-level cell (SLC) devices, each cell stores only one bit of information. Some newer flash memory, known as multi-level cell (MLC) devices, can store more than one bit per cell by choosing between multiple levels of electrical charge to apply to the floating gates of its cells(SONY VAIO PCG-8Y1L battery).

The floating gate may be conductive (typically polysilicon in most kinds of flash memory) or non-conductive (as in SONOS flash memory).

Floating-gate transistor

In flash memory, each memory cell resembles a standard MOSFET, except the transistor has two gates instead of one(SONY VAIO PCG-7Z2L battery). On top is the control gate (CG), as in other MOS transistors, but below this there is a floating gate (FG) insulated all around by an oxide layer. The FG is interposed between the CG and the MOSFET channel. Because the FG is electrically isolated by its insulating layer(SONY VAIO PCG-7Z1L battery), any electrons placed on it are trapped there and, under normal conditions, will not discharge for many years. When the FG holds a charge, it screens (partially cancels) the electric field from the CG, which modifies the threshold voltage (VT) of the cell. During read-out(SONY VAIO PCG-7133L battery), a voltage intermediate between the possible threshold voltages is applied to the CG, and the MOSFET channel will become conducting or remain insulating, depending on the VT of the cell, which is in turn controlled by charge on the FG(SONY VAIO PCG-7113L battery). The current flow through the MOSFET channel is sensed and forms a binary code, reproducing the stored data. In a multi-level cell device, which stores more than one bit per cell, the amount of current flow is sensed (rather than simply its presence or absence), in order to determine more precisely the level of charge on the FG(SONY VAIO PCG-6W3L battery).

NOR flash

In NOR gate flash, each cell has one end connected directly to ground, and the other end connected directly to a bit line.

This arrangement is called "NOR flash" because it acts like a NOR gate: when one of the word lines is brought high, the corresponding storage transistor acts to pull the output bit line low(SONY VAIO PCG-7111L battery).

Programming

A single-level NOR flash cell in its default state is logically equivalent to a binary "1" value, because current will flow through the channel under application of an appropriate voltage to the control gate. A NOR flash cell can be programmed, or set to a binary "0" value, by the following procedure(SONY VAIO PCG-6W1L battery):

an elevated on-voltage (typically >5 V) is applied to the CG

the channel is now turned on, so electrons can flow from the source to the drain (assuming an NMOS transistor)

the source-drain current is sufficiently high to cause some high energy electrons to jump through the insulating layer onto the FG, via a process called hot-electron injection(SONY VAIO PCG-6V1L battery)

Erasing

To erase a NOR flash cell (resetting it to the "1" state), a large voltage of the opposite polarity is applied between the CG and source, pulling the electrons off the FG through quantum tunneling. Modern NOR flash memory chips are divided into erase segments (often called blocks or sectors) (SONY VAIO PCG-6S3L battery). The erase operation can only be performed on a block-wise basis; all the cells in an erase segment must be erased together. Programming of NOR cells, however, can generally be performed one byte or word at a time(SONY VAIO PCG-6S2L battery).

Internal charge pumps

Despite the need for high programming and erasing voltages, virtually all flash chips today require only a single supply voltage, and produce the high voltages via on-chip charge pumps(SONY VAIO PCG-5J2L battery).

NAND flash

NAND flash also uses floating-gate transistors, but they are connected in a way that resembles a NAND gate: several transistors are connected in series, and only if all word lines are pulled high (above the transistors' VT) is the bit line pulled low. These groups are then connected via some additional transistors to a NOR-style bit line array(SONY VAIO PCG-5L1L battery).

To read, most of the word lines are pulled up above the VT of a programmed bit, while one of them is pulled up to just over the VT of an erased bit. The series group will conduct (and pull the bit line low) if the selected bit has not been programmed(SONY VAIO PCG-5K2L battery).

Despite the additional transistors, the reduction in ground wires and bit lines allows a denser layout and greater storage capacity per chip. In addition, NAND flash is typically permitted to contain a certain number of faults (NOR flash, as is used for a BIOS ROM, is expected to be fault-free) (SONY VAIO PCG-5J1L battery). Manufacturers try to maximize the amount of usable storage by shrinking the size of the transistor below the size where they can be made reliably, to the size where further reductions would increase the number of faults faster than it would increase the total storage available(SONY VAIO PCG-5G3L battery).

NAND flash uses tunnel injection for writing and tunnel release for erasing. NAND flash memory forms the core of the removable USB storage devices known as USB flash drives, as well as most memory card formats and solid-state drives available today(SONY VAIO PCG-5G2L battery).

Block erasure

One limitation of flash memory is that although it can be read or programmed a byte or a word at a time in a random access fashion, it can only be erased a "block" at a time. This generally sets all bits in the block to 1. Starting with a freshly erased block, any location within that block can be programmed(SONY VGP-BPS13B/S Battery). However, once a bit has been set to 0, only by erasing the entire block can it be changed back to 1. In other words, flash memory (specifically NOR flash) offers random-access read and programming operations, but cannot offer arbitrary random-access rewrite or erase operations(SONY VGP-BPS13S Battery). A location can, however, be rewritten as long as the new value's 0 bits are a superset of the over-written value's. For example, a nibble value may be erased to 1111, then written as 1110. Successive writes to that nibble can change it to 1010, then 0010, and finally 0000(SONY VGP-BPS13AS Battery). Essentially, erasure sets (all) bits, and programming can only clear bits. Filesystems designed for flash devices can make use of this capability to represent sector metadata(SONY VGP-BPS13A/S Battery).

Although data structures in flash memory cannot be updated in completely general ways, this allows members to be "removed" by marking them as invalid. This technique may need to be modified for Multi-level Cell devices, where one memory cell holds more than one bit(Sony VAIO VGN-FZ15G Battery).

Common flash devices such as USB keys and memory cards provide only a block-level interface, or flash translation layer (FTL), which writes to a different cell each time to wear-level the device(Sony VAIO VGN-FZ15T Battery). This prevents incremental writing within a block, however it does help the device from being prematurely worn out by abusive and/or poorly designed hardware/software. For example, nearly all consumer devices ship formatted with MS-FAT file system, which pre-dates flash memory, having been designed for DOS, and disk media(SONY VGP-BPS13/B Battery).

Memory wear

Another limitation is that flash memory has a finite number of program-erase cycles (typically written as P/E cycles). Most commercially available flash products are guaranteed to withstand around 100,000 P/E cycles(Dell N3010 Battery), before the wear begins to deteriorate the integrity of the storage. Micron Technology and Sun Microsystems announced an SLC flash memory chip rated for 1,000,000 P/E cycles on December 17, 2008(Dell INSPIRON 1764 battery).

The guaranteed cycle count may apply only to block zero (as is the case with TSOP NAND parts), or to all blocks (as in NOR). This effect is partially offset in some chip firmware or file system drivers by counting the writes and dynamically remapping blocks in order to spread write operations between sectors; this technique is called wear leveling(Dell INSPIRON 1564 battery). Another approach is to perform write verification and remapping to spare sectors in case of write failure, a technique called Bad Block Management (BBM). For portable consumer devices, these wearout management techniques typically extend the life of the flash memory beyond the life of the device itself, and some data loss may be acceptable in these applications(Dell INSPIRON 1464 battery). For high reliability data storage, however, it is not advisable to use flash memory that would have to go through a large number of programming cycles. This limitation is meaningless for 'read-only' applications such as thin clients and routers, which are only programmed once or at most a few times during their lifetimes(Dell INSPIRON 1520 battery).

he low-level interface to flash memory chips differs from those of other memory types such as DRAM, ROM, and EEPROM, which support bit-alterability (both zero to one and one to zero) and random-access via externally accessible address buses(Dell INSPIRON 1420 battery).

While NOR memory provides an external address bus for read and program operations (and thus supports random-access); unlocking and erasing NOR memory must proceed on a block-by-block basis. With NAND flash memory, read and programming operations must be performed page-at-a-time while unlocking and erasing must happen in block-wise fashion(Dell INSPIRON E1505 battery).

NOR memories

Reading from NOR flash is similar to reading from random-access memory, provided the address and data bus are mapped correctly. Because of this, most microprocessors can use NOR flash memory as execute in place (XIP) memory(Dell INSPIRON 1525 battery), meaning that programs stored in NOR flash can be executed directly from the NOR flash without needing to be copied into RAM first. NOR flash may be programmed in a random-access manner similar to reading(SONY VGP-BPS13B/B Battery). Programming changes bits from a logical one to a zero. Bits that are already zero are left unchanged. Erasure must happen a block at a time, and resets all the bits in the erased block back to one. Typical block sizes are 64, 128, or 256 KB(SONY VGP-BPS13 Battery).

Bad block management is a relatively new feature in NOR chips. In older NOR devices not supporting bad block management, the software or device driver controlling the memory chip must correct for blocks that wear out, or the device will cease to work reliably(HP PAVILION DV6000 battery).

The specific commands used to lock, unlock, program, or erase NOR memories differ for each manufacturer. To avoid needing unique driver software for every device made, a special set of Common Flash Memory Interface (CFI) commands allow the device to identify itself and its critical operating parameters(SONY VAIO VGN-FZ31B Battery).

Apart from being used as random-access ROM, NOR memories can also be used as storage devices by taking advantage of random-access programming(SONY VAIO VGN-FZ31M Battery). Some devices offer read-while-write functionality so that code continues to execute even while a program or erase operation is occurring in the background. For sequential data writes, NOR flash chips typically have slow write speeds compared with NAND flash(SONY VAIO VGN-FZ31J Battery).

NAND memories

NAND flash architecture was introduced by Toshiba in 1989. These memories are accessed much like block devices such as hard disks or memory cards. Each block consists of a number of pages. The pages are typically 512 or 2,048 or 4,096 bytes in size. Associated with each page are a few bytes (typically 1/32 of the data size) that can be used for storage of an error correcting code (ECC) checksum(SONY VAIO VGN-FZ31E Battery).

Typical block sizes include:

32 pages of 512+16 bytes each for a block size of 16 KB

64 pages of 2,048+64 bytes each for a block size of 128 KB

64 pages of 4,096+128 bytes each for a block size of 256 KB

128 pages of 4,096+128 bytes each for a block size of 512 KB(Sony Vaio VGN-FZ31S battery).

While reading and programming is performed on a page basis, erasure can only be performed on a block basis.Another limitation of NAND flash is data in a block can only be written sequentially. Number of Operations (NOPs) is the number of times the sectors can be programmed. So far this number for MLC flash is always one whereas for SLC flash it is four(SONY VAIO VGN-FZ31z Battery).

NAND devices also require bad block management by the device driver software, or by a separate controller chip. SD cards, for example, include controller circuitry to perform bad block management and wear leveling(SONY VAIO VGN-FZ38M Battery). When a logical block is accessed by high-level software, it is mapped to a physical block by the device driver or controller. A number of blocks on the flash chip may be set aside for storing mapping tables to deal with bad blocks, or the system may simply check each block at power-up to create a bad block map in RAM(SONY VAIO VGN-FZ210CE Battery). The overall memory capacity gradually shrinks as more blocks are marked as bad.

NAND relies on ECC to compensate for bits that may spontaneously fail during normal device operation. A typical ECC will correct a one bit error in each 2048 bits (256 bytes) using 22 bits of ECC code, or a one bit error in each 4096 bits (512 bytes) using 24 bits of ECC code. If ECC cannot correct the error during read, it may still detect the error(SONY VAIO VGN-FZ160 Battery). When doing erase or program operations, the device can detect blocks that fail to program or erase and mark them bad. The data is then written to a different, good block, and the bad block map is updated(SONY VAIO VGN-FZ21 Battery).

Most NAND devices are shipped from the factory with some bad blocks which are typically identified and marked according to a specified bad block marking strategy. By allowing some bad blocks(SONY VAIO VGN-FZ410 Battery), the manufacturers achieve far higher yields than would be possible if all blocks had to be verified good. This significantly reduces NAND flash costs and only slightly decreases the storage capacity of the parts(SONY VAIO VGN-FZ21m Battery).

When executing software from NAND memories, virtual memory strategies are often used: memory contents must first be paged or copied into memory-mapped RAM and executed there (leading to the common combination of NAND + RAM). A memory management unit (MMU) in the system is helpful(SONY VAIO VGN-FZ18m Battery), but this can also be accomplished with overlays. For this reason, some systems will use a combination of NOR and NAND memories, where a smaller NOR memory is used as software ROM and a larger NAND memory is partitioned with a file system for use as a non-volatile data storage area(SONY VAIO VGN-FZ11m Battery).

NAND is best suited to systems requiring high capacity data storage. This type of flash architecture offers higher densities and larger capacities at lower cost with faster erase, sequential write, and sequential read speeds, sacrificing the random-access and execute in place advantage of the NOR architecture(SONY VAIO VGN-FZ11z Battery).

Standardization

A group called the Open NAND Flash Interface Working Group (ONFI) has developed a standardized low-level interface for NAND flash chips. This allows interoperability between conforming NAND devices from different vendors. The ONFI specification version 1.0 was released on December 28, 2006. It specifies(SONY VAIO VGN-FZ11l Battery):

a standard physical interface (pinout) for NAND flash in TSOP-48, WSOP-48, LGA-52, and BGA-63 packages

a standard command set for reading, writing, and erasing NAND flash chips

a mechanism for self-identification (comparable to the Serial Presence Detection feature of SDRAM memory modules) (SONY VAIO VGN-FZ140E Battery)

The ONFI group is supported by major NAND flash manufacturers, including Hynix, Intel, Micron Technology, and Numonyx, as well as by major manufacturers of devices incorporating NAND flash chips(SONY VAIO VGN-FZ260E Battery).

A group of vendors, including Intel, Dell, and Microsoft formed a Non-Volatile Memory Host Controller Interface (NVMHCI) Working Group. The goal of the group is to provide standard software and hardware programming interfaces for nonvolatile memory subsystems, including the "flash cache" device connected to the PCI Express bus(SONY VAIO VGN-FZ150E Battery).

Distinction between NOR and NAND flash

NOR and NAND flash differ in two important ways:

the connections of the individual memory cells are different

the interface provided for reading and writing the memory is different (NOR allows random-access for reading, NAND allows only page access) (SONY VAIO VGN-FZ190 Battery)

These two are linked by the design choices made in the development of NAND flash. A goal of NAND flash development was to reduce the chip area required to implement a given capacity of flash memory, and thereby to reduce cost per bit and increase maximum chip capacity so that flash memory could compete with magnetic storage devices like hard disks(SONY VAIO VGN-FZ460E Battery).

NOR and NAND flash get their names from the structure of the interconnections between memory cells.In NOR flash, cells are connected in parallel to the bit lines, allowing cells to be read and programmed individually(SONY VAIO VGN-FZ280E Battery). The parallel connection of cells resembles the parallel connection of transistors in a CMOS NOR gate. In NAND flash, cells are connected in series, resembling a NAND gate. The series connections consume less space than parallel ones, reducing the cost of NAND flash(SONY VAIO VGN-FZ440N Battery). It does not, by itself, prevent NAND cells from being read and programmed individually.

When NOR flash was developed, it was envisioned as a more economical and conveniently rewritable ROM than contemporary EPROM and EEPROM memories. Thus random-access reading circuitry was necessary(SONY VAIO VGN-FZ32 Battery). However, it was expected that NOR flash ROM would be read much more often than written, so the write circuitry included was fairly slow and could only erase in a block-wise fashion(sony vgp-bpl9 battery). On the other hand, applications that use flash as a replacement for disk drives do not require word-level write address, which would only add to the complexity and cost unnecessarily(SONY vgp-bps9 battery).

Because of the series connection and removal of wordline contacts, a large grid of NAND flash memory cells will occupy perhaps only 60% of the area of equivalent NOR cells(assuming the same CMOS process resolution, e.g(SONY VAIO VGN-FZ11S Battery). 130nm, 90 nm, 65 nm). NAND flash's designers realized that the area of a NAND chip, and thus the cost, could be further reduced by removing the external address and data bus circuitry(SONY VAIO VGN-FZ Battery). Instead, external devices could communicate with NAND flash via sequential-accessed command and data registers, which would internally retrieve and output the necessary data. This design choice made random-access of NAND flash memory impossible, but the goal of NAND flash was to replace hard disks, not to replace ROMs(SONY VGP-BPS8 battery).

Write endurance

The write endurance of SLC floating-gate NOR flash is typically equal or greater than that of NAND flash, while MLC NOR and NAND flash have similar endurance capabilities. Example Endurance cycle ratings listed in datasheets for NAND and NOR flash are provided(Sony VAIO PCG-5K1L battery).

SLC NAND flash is typically rated at about 100k cycles (Samsung OneNAND KFW4G16Q2M)

MLC NAND flash is typically rated at about 5–10k cycles (Samsung K9G8G08U0M)

SLC floating-gate NOR flash has typical endurance rating of 100k to 1M cycles (Numonyx M58BW 100k; Spansion S29CD016J 1,000k) (Sony VAIO PCG-6W2L battery)

MLC floating-gate NOR flash has typical endurance rating of 100k cycles (Numonyx J3 flash)

However, by applying certain algorithms and design paradigms such as wear leveling and memory over-provisioning, the endurance of a storage system can be tuned to serve specific requirements(Sony VAIO PCG-7112L battery).

Flash file systems

Because of the particular characteristics of flash memory, it is best used with either a controller to perform wear leveling and error correction or specifically designed flash file systems, which spread writes over the media and deal with the long erase times of NOR flash blocks(Sony VAIO PCG-8Z1L battery). The basic concept behind flash file systems is: When the flash store is to be updated, the file system will write a new copy of the changed data to a fresh block, remap the file pointers, then erase the old block later when it has time(Sony VAIO PCG-8Z2L battery).

In practice, flash file systems are only used for memory technology devices (MTDs), which are embedded flash memories that do not have a controller. Removable flash memory cards and USB flash drives have built-in controllers to perform wear leveling and error correction so use of a specific flash file system does not add any benefit(Sony VAIO PCG-8Y2L battery).

Capacity

Multiple chips are often arrayed to achieve higher capacities for use in consumer electronic devices such as multimedia players or GPS. The capacity of flash chips generally follows Moore's Law because they are manufactured with many of the same integrated circuits techniques and equipment(Sony VAIO PCG-8Y1L battery).

Consumer flash drives typically have sizes measured in powers of two (e.g., 512 MB, 8 GB). This includes SSDs as hard drive replacements, even though traditional hard drives tend to use decimal units(Sony VAIO PCG-7Z2L battery). Thus, an SSD marked as "64 GB" is actually 64 × 1,0243 bytes (64 GB). In reality, most users will have slightly less capacity than this available, due to the space taken by file system metadata(Sony VAIO PCG-7Z1L battery).

In 2005, Toshiba and SanDisk developed a NAND flash chip capable of storing 1 GB of data using multi-level cell (MLC) technology, capable of storing two bits of data per cell. In September 2005, Samsung Electronics announced that it had developed the world’s first 2 GB chip(Sony VAIO PCG-7133L battery).

In March 2006, Samsung announced flash hard drives with a capacity of 4 GB, essentially the same order of magnitude as smaller laptop hard drives, and in September 2006, Samsung announced an 8 GB chip produced using a 40-nm manufacturing process.[21] In January 2008, Sandisk announced availability of their 16 GB MicroSDHC and 32 GB SDHC Plus cards(Sony VAIO PCG-7113L battery).

In 2009, Kingston announced a 256 GB flash drive available only in the UK and other parts of Europe. As of 2010, however, it is available in the USA.

There are still flash-chips manufactured with capacities under or around 1 MB, e.g., for BIOS-ROMs and embedded applications(Sony VAIO PCG-6W3L battery).

Transfer rates

NAND flash memory cards are much faster at reading than writing so it is the maximum read speed that is commonly advertised(Sony VAIO PCG-7111L battery).

As a chip wears out, its erase/program operations slow down considerably,[citation needed] requiring more retries and bad block remapping. Transferring multiple small files, each smaller than the chip-specific block size, could lead to much a lower rate. Access latency also influences performance, but less so than with their hard drive counterpart(Sony VAIO PCG-6W1L battery).

The speed is sometimes quoted in MB/s (megabytes per second), or as a multiple of that of a legacy single speed CD-ROM, such as 60×, 100× or 150×. Here 1× is equivalent to 150 kB/s. For example, a 100× memory card gives 150 kB/s × 100 = 15,000 kB/s = 14.65 MB/s(Sony VAIO PCG-6V1L battery).

Performance also depends on the quality of memory controllers. Even when the only change to manufacturing is die-shrink, the absence of an appropriate controller can result in degraded speeds(Sony VAIO PCG-6S3L battery).

Applications

Serial flash

Serial flash is a small, low-power flash memory that uses a serial interface, typically SPI, for sequential data access. When incorporated into an embedded system, serial flash requires fewer wires on the PCB than parallel flash memories, since it transmits and receives data one bit at a time. This may permit a reduction in board space, power consumption, and total system cost(Sony VAIO PCG-6S2L battery).

There are several reasons why a serial device, with fewer external pins than a parallel device, can significantly reduce overall cost(Sony VAIO PCG-5L1L battery):

Many ASICs are pad-limited, meaning that the size of the die is constrained by the number of wire bond pads, rather than the complexity and number of gates used for the device logic(Sony VAIO PCG-5K2L battery). Eliminating bond pads thus permits a more compact integrated circuit, on a smaller die; this increases the number of dies that may be fabricated on a wafer, and thus reduces the cost per die(Sony VAIO PCG-5J2L battery).

Reducing the number of external pins also reduces assembly and packaging costs. A serial device may be packaged in a smaller and simpler package than a parallel device(Sony VAIO PCG-5J1L battery).

Smaller and lower pin-count packages occupy less PCB area.

Lower pin-count devices simplify PCB routing.

There are two major SPI flash types. The Atmel AT45 DataFlas was the first type and is characterized by small pages and one or more internal SRAM page buffers allowing a complete page to be read to the buffer(Sony VAIO PCG-5G3L battery), partially modified, and then written back. The second type is called SPI flash and typically has larger sectors. The smallest sectors typically found in an SPI flash are 4 kB, but they can be as large as 64 kB. Since the SPI flash lacks an internal SRAM buffer, the complete page must be read out and modified before written back, making it slow to manage(Sony VAIO PCG-5G2L battery). SPI flash is cheaper than DataFlash and is therefore a good choice when the application is code shadowing.

The two types are not easily exchangeable, since they do not have the same pinout. and the command sets are also incompatible(Sony VGP-BPS21A/B battery).

Firmware storage

With the increasing speed of modern CPUs, parallel flash devices are often much slower than the memory bus of the computer they are connected to. Conversely, modern SRAM offers access times below 10 ns, while DDR2 SDRAM offers access times below 20 ns. Because of this, it is often desirable to shadow code stored in flash into RAM(Sony VGP-BPS21/S battery); that is, the code is copied from flash into RAM before execution, so that the CPU may access it at full speed. Device firmware may be stored in a serial flash device, and then copied into SDRAM or SRAM when the device is powered-up(Sony VGP-BPS21B battery). Using an external serial flash device rather than on-chip flash removes the need for significant process compromise (a process that is good for high speed logic is generally not good for flash and vice-versa) (Sony VGP-BPS21 battery). Once it is decided to read the firmware in as one big block it is common to add compression to allow a smaller flash chip to be used. Typical applications for serial flash include storing firmware for hard drives, Ethernet controllers, DSL modems, wireless network devices, etc(Sony VGP-BPS13A/S battery).

Flash memory as a replacement for hard drives

One more recent application for flash memory is as a replacement for hard disks. Flash memory does not have the mechanical limitations and latencies of hard drives, so a solid-state drive, or SSD, is attractive when considering speed(Sony VGP-BPS13B/S battery), noise, power consumption, and reliability. Flash drives are gaining traction as mobile device secondary storage devices; they are also used as hard drives in high-performance desktop computers and some servers with RAID and SAN architectures(Sony VGP-BPS13S battery).

There remain some aspects of flash-based SSDs that make them unattractive. Most important, the cost per gigabyte of flash memory remains significantly higher than that of platter-based hard drives(Sony VGP-BPS13AS battery). Although this ratio is decreasing rapidly for flash memory, it is not yet clear that flash memory will catch up to the capacities and affordability offered by platter-based storage. Still, research and development is sufficiently vigorous that it is not clear that it will not happen, either(Sony PCGA-BP2EA battery).

There is also some concern that the finite number of P/E cycles of flash memory would render flash memory unable to support an operating system. This seems to be a decreasing issue as warranties on flash-based SSDs are approaching those of current hard drives(Sony VGP-BPS13/B battery).

In June 2006, Samsung Electronics released the first flash-memory based PCs, the Q1-SSD and Q30-SSD, both of which used 32 GB SSDs, and were at least initially available only in South Korea(Sony VGP-BPS13/S battery). Dell Computer introduced a 32GB SSD option on its Latitude D420 and D620 ATG laptops in April 2007—at $549 more than a hard-drive equipped version. At the Las Vegas CES 2007 Summit Taiwanese memory company A-DATA showcased SSD hard disk drives based on flash technology in capacities of 32 GB, 64 GB and 128 GB. Sandisk announced an OEM 32 GB 1.8" SSD drive at CES 2007(Sony VGP-BPS13A/B battery). The XO-1, developed by the One Laptop Per Child (OLPC) association, uses flash memory rather than a hard drive. As of March 2009, a Salt Lake City company called Fusion-io claims the fastest SSD with sequential read/write speeds of 1500 MB/1400 MB's per second(Sony VGP-BPS13B/B battery).

Rather than entirely replacing the hard drive, hybrid techniques such as hybrid drive and ReadyBoost attempt to combine the advantages of both technologies, using flash as a high-speed cache for files on the disk that are often referenced(Sony VGN-FZ11E battery), but rarely modified, such as application and operating system executable files. Also, Addonics has a PCI adapter for four CF cards, creating a RAID-able array of solid-state storage that is much cheaper than the hardwired-chips PCI card kind(Sony VGN-FZ430E battery).

Early versions of the ASUS Eee PC used a flash-based SSD of 2 GB to 20 GB, depending on model, although later versions of the machine use conventional hard disks. The Apple Inc. Macbook Air has the option to upgrade the standard hard drive to a 128 GB Solid State hard drive. The Lenovo ThinkPad X300 also features a built-in 64 GB Solid State Drive. The Apple iPad has flash-based SSD's of 16, 32, and 64 GB(Sony VGN-FZ32 battery).

Sharkoon has developed a device that uses six SDHC cards in RAID-0 configuration as an SSD alternative; users may use more affordable High-Speed 8 GB SDHC cards to get similar or better results than can be obtained from traditional SSDs at a lower cost(Sony VGN-FZ440N battery).

In Mid 2010, Apple Inc, introduced Mac Book Air notebooks which use flash as the primary device of storage instead of hard drives. However, Apple has already seen success with this hardware model in its most successful iPhones and iPads(Sony VGN-FZ52B2 battery).

Flash scalability

Due to its relatively simple structure and high demand for higher capacity, NAND flash memory is the most aggressively scaled technology among electronic devices. The heavy competition among the top few manufacturers only adds to the aggressiveness(Sony VGN-FZ52B battery). Current projections show the technology to reach approximately 20 nm by around late 2011. While the expected shrink timeline is a factor of two every three years per original version of Moore's law, this has recently been accelerated in the case of NAND flash to a factor of two every two years(Sony VGN-FZ51B battery).

As the feature size of flash memory cells reach the minimum limit (currently estimated ~20 nm), further flash density increases will be driven by greater levels of MLC, possibly 3-D stacking of transistors, and improvements to the manufacturing process(Sony VGN-FZ50B battery). The decrease in endurance and increase in uncorrectable bit error rates that accompany feature size shrinking can be compensated by improved error correction mechanisms. Even with these advances, it may be impossible to economically scale flash to smaller and smaller dimensions(Sony VGN-FZ340E/B battery). Many promising new technologies (such as FeRAM, MRAM, PMC, PCM, and others) are under investigation and development as possible more scalable replacements for flash(Sony VGN-FZ38 battery).

10 things Linux does better than OS X

It may sound strange, seeing as how OS X is based on a Linux variant and is widely considered to be the most user-friendly operating system available, but Linux does a number of things better than everyone’s favorite iOperatingSystem(SONY VAIO VGN-FZ31B Battery). Before you shun the thought, read on. You might be surprised at your resulting opinion.

#1: Flexibility

If you’ve used OS X, you know it’s user-friendly but not very flexible. In that regard, OS X is very much like Windows: You get what you have and there’s not much you can do with it(SONY VAIO VGN-FZ31M Battery). If you don’t like the layout of the desktop, you can move the Dock to either side, you can shrink it, or you can make it auto-hide. You can also add third-party applications and themes the desktop. Outside of that, you’re out of luck. Say, for example(SONY VAIO VGN-FZ31J Battery), you would like to have only the Dock on your desktop (with the taskbar features integrated). You can’t do it. That taskbar is as much a part of OS X as the Blue Screen of Death was in Windows 95. Linux is a different story. You don’t want the taskbar but you like its features(SONY VAIO VGN-FZ31E Battery)? No problem. Add whatever features to whate

ver taskbar or panel you want. Linux can pretty much take any configuration you throw at it. And if you still don’t like what you have, install a different desktop or window manager and you’re good to go(Sony Vaio VGN-FZ31S battery).

#2: Open source

One of the biggest issues that Linux users have with OS X is the license. Apple took a BSD kernel to create its own Darwin kernel, released it under the Apple Public Source License (which was accepted by the Free Software Foundation) (SONY VAIO VGN-FZ31z Battery), and then layered on top of that proprietary software to create OS X. At one point, Apple created OpenDarwin, which was a collaborative effort between Apple and the open source community. That project lasted four years before Apple took it down because it felt the effort to create an open source Darwin operating system had failed(SONY VAIO VGN-FZ38M Battery). In 2007, PureDarwin was created to continue the work that was developed with OpenDarwin. The PureDarwin project has come a long way and can even run Linux-based window managers (such as Enlightenment) on top of it. OS X, however, is still locked tightly together and can’t compete with the openness of Linux(SONY VAIO VGN-FZ210CE Battery).

#3: Command line

Although most OS X users would balk at this (saying they have no use for the command line), most power users know the command line is crucial to serious administrative tasks. In this department, OS X falls way short of Linux(SONY VAIO VGN-FZ160 Battery). With Linux, you can do pretty much everything you need from the command line. With OS X? Good luck. Sure, OS X does have a fairly good set of command-line tools, but for the power admin, it’s just not enough(SONY VAIO VGN-FZ21 Battery). This is one area of OS X that I simply can’t figure out. Why didn’t Apple just migrate the Linux coreutils over to OS X? There are projects aimed at getting coreutils to compile on OS X, but it would have made more sense to have this by default. The coreutils package is a huge toolkit that contains nearly every basic command you need. OS X had to reinvent that wheel(SONY VAIO VGN-FZ410 Battery). But this goes beyond the coreutils package. What about installing via command line? What about command-line security? What about starting/stopping services from the command line(SONY VAIO VGN-FZ21m Battery)?

#4: Hardware requirements

I have two Macs in my household. One Mac is an old iBook running at 800 Mhz with a 512 MB of RAM. That machine is slow with OS X running on it. But with Yellow Dog Linux, that little laptop runs much snappier(SONY VAIO VGN-FZ18m Battery). Same hardware, different OS. The other Mac is a G4 1.2 processor with 1 GB of RAM. I have an equivalent Intel machine running Ubuntu 8.10. The machines do not even compare in performance(SONY VAIO VGN-FZ11m Battery). The Ubuntu machine is faster on all levels (from boot to application launch). Taking a look at the minimum system requirements for OS X and Ubuntu, you see:

OS X: 876 MHz or faster CPU, 512 MB of RAM, 9 GB of disk space

Ubuntu: 700 MHz x86 processor , 384 MB ofRAM, and 8 GB of disk space

So obviously Linux can run on lesser powered machines by default. And Ubuntu 8.10 is not the most optimized of the Linux distributions. Mandriva Spring 2008 has even fewer requirements (claiming to run on ANY CPU and only 256 MB of RAM) (SONY VAIO VGN-FZ11z Battery).

I have read of benchmarking tests claiming that OS X outperforms Ubuntu 8.10 soundly. But real world results would seem to contradict those claims. I ran a less-than-scientific test with the Mac iBook G4 1.2 and the Ubuntu 8.10 on a 1.2 processor. Both machines had 512 MB of RAM(SONY VAIO VGN-FZ11l Battery). On the Ubuntu machine (running the Enlightenment window manager), I was able to open up the following applications before the machine began to bog down: Firefox, OpenOffice Writer, OpenOffice Calc, OpenOffice Impress, Scribus, The Gimp, Amarok, GnuCash, Thunderbird, Basket, Audacity, Gqview, and aterm(SONY VAIO VGN-FZ140E Battery). The OS X machine was a different story. With OpenOffice, Firefox, Thunderbird, and iTunes open, the machine started to crawl. There was a noticeable degradation in performance. That’s an OS running 14 applications vs an OS running four applications before the OS comes to a crawl. I don’t know about you, but I would prefer the ability to run 14 apps(SONY VAIO VGN-FZ260E Battery).

#5: Security

In the most recent “Pwn 2 Own” competition, both the OS X and the Windows Vista machines were hacked, whereas the Linux machine was not. Of course there are pundits across the globe who will argue this one from all three sides, and finding unbiased results is akin to finding a definitive answer to the age-old TCO argument(SONY VAIO VGN-FZ150E Battery). But I can say, unequivocally, after 10-plus years of experience with Linux, that I have never had a machine or server compromised in any way. This, of course, is not to say that OS X is unsecure. But Linux simply is better equipped in the area of security. How? Tools. With tools like iptables, fwbuilder(SONY VAIO VGN-FZ190 Battery), and SELinux, Linux can lock down in many ways, on many levels. So you take a similar kernel but you add to that kernel-level tools to heighten security, and you can quickly see how Linux overpowers OS X in the area of security(SONY VAIO VGN-FZ460E Battery).

6. Portability

Another area where Linux shines over all other operating systems is in its ability to migrate an installation from hardware to hardware. Linux has an uncanny ability to be able to relocate. I have taken complete hard drives and moved them from one machine to another(SONY VAIO VGN-FZ280E Battery). So long as the architecture was the same (in other words, not moving from a x86 to an x86_64 machine), the migration always seemed to work with little to no adjusting. OS X, on the other hand, is landlocked to the machine it was installed in. Also, with Linux, you can take certain directories and move them from machine to machine. This works well with the /home directory(SONY VAIO VGN-FZ440N Battery). Having the ability to migrate your /home directory from one machine to another can make building machines a snap. With OS X, you’ll always be reinstalling from scratch(SONY VAIO VGN-FZ32 Battery).

#7: Cost

This is a big one for many people. First, you have the cost of the operating system alone. Linux is free. Period. OS X is currently selling for $129.00. Next is hardware cost. The cheapest Macbook you can purchase is $999.00. You can purchase a $399.00 laptop that will run Linux like a champ from any given dealer(sony vgp-bpl9 battery). Add on top of that the cost of the software you will need, and you can run up a fairly large tab. Linux? Nada. You can have an office-ready Linux machine that will tackle most every task you put to it for the cost of the hardware alone(SONY vgp-bps9 battery). Mac? Not so much. So if you’re looking to cut costs (and who isn’t, in this economy?), Linux is the way to go.

#8: More available software

This may come as a surprise to you, but Linux has far more software available than OS X. In a completely unscientific test, I did a search for both Linux and OS X on freshmeat.net (an index of UNIX and cross-platform software) (SONY VAIO VGN-FZ11S Battery). Here are the numbers: Linux 11,781 results. OS X 1,477 results. Of course, many would say that it’s not a fair search because freshmeat.net is decidedly an open source leaning repository. With that in mind, lets turn to Google and search for OS X Software and Linux Software. The results: OS X 19,100,000 hits. Linux 45,700,000 hits(SONY VAIO VGN-FZ Battery).

One of the things that separates Linux from all other operating systems is that for every task in Linux, there are numerous tools available to undertake it. Let’s look at the task of word processing(SONY VGP-BPS8 battery). For Mac, you have Microsoft Office and OpenOffice as the major players, and then you have minor players, like Bean, Nisus, Mellel, and NeoOffice. With Linux, you have the major player OpenOffice, and then you have the minor players Textmaker, Abiword, Hangul, EZ, Kwrite, gedit, nano, vi, emacs, Flwriter, Ted, Siag Office, LaTeX, EditPad Pro, etc. You get the picture. And yes, you can install Linux apps on OS X with Fink. I’ve done this(Sony VAIO PCG-5K1L battery). It’s not a good solution because the software often is prone to crashing or not running at all.

#9: Not so dumbed-down

I have tried to come up with the phrase that is the opposite of “dumbed down,” but I’ve had no luck. So work with me on this one. One thing that Apple did very well with OS X is dumb down the operating system interface to the point where most all tasks are easy for anyone to do(Sony VAIO PCG-6W2L battery). But there are those who do not want that dumbed-down experience. With Linux, you can have a desktop experience on every level. You can have the full-on, dumbed-down experience akin to OS X with either GNOME or KDE. Or you can go to the complete opposite and use the console as your desktop. Or you can experience anything and everything in between the two(Sony VAIO PCG-7112L battery). With OS X, many power users feel like someone is holding their hand throughout the experience. With Linux, you can let go of that hand from time to time or even chop the hand off and replace it with a hook. When you’re using the Apple desktop, OS X is in control. When you use the Linux desktop, you are in control(Sony VAIO PCG-8Z1L battery).

#10: Keyboard efficiency

One of my biggest pet peeves with OS X is the fact that there is no normally functioning Delete key. Instead you have to hit fn + Delete to get the delete key to work as it should. This is pretty common practice with the OS X keyboard(Sony VAIO PCG-8Z2L battery), which is about as efficient to a hard-core programmer as a salad is tasty. And it’s not just the Delete key. The End key doesn’t do what you would expect, either. To get to the end of the line, you have to add the fn key to the End key (so fn + End will get you to the end of the line.) Another issue — mouse buttons. I know this is a fundamental design that makes sense to Apple(Sony VAIO PCG-8Y2L battery). But the majority of people like two mouse buttons. And with Linux, you actually get THREE mouse buttons. With those three mouse buttons, you can even do a simple copy and paste function (highlight text with a left mouse button and then click the middle mouse button to paste). The Linux keyboard is just far more efficient than the OS X keyboard(Sony VAIO PCG-8Y1L battery).

Other issues

Those are 10 simple things Linux does better than OS X. Are any of the above deal-breakers? Quite possibly. Do you have an issue with OS X that Linux handles better? If so let us know(Sony VAIO PCG-7Z2L battery).

The industry's 10 best IT certifications

IT certifications boast numerous benefits. They bolster resumes, encourage higher salaries, and assist in job retention. But which IT certifications are best(SONY VGP-BPS21/S Battery)?

Technology professionals generate much debate over just that question. Many claim vendor-specific programs best measure a candidate’s skills, while others propose vendor-independent exams are the only worthy way of measuring real-world expertise(SONY VGP-BPS21 Battery). Still other observers believe the highest-level accreditations — Microsoft’s MCSE or new Architect Series certification, Cisco’s CCIE, etc. — are the only credentials that truly hold value(SONY VGP-BPS21B Battery).

Myself, I don’t fully subscribe to any of those mindsets. The best IT certification for you, after all, is likely to be different from that for another technology professional with different education, skills, and goals working at a different company in a different industry(SONY VGP-BPS21A/B Battery). For that reason, when pursuing any professional accreditation, you should give much thought and care to your education, experience, skills, goals, and desired career path(SONY pcga-bp2ea battery).

Once a career road map is in place, selecting a potential certification path becomes much easier. And that’s where this list of the industry’s 10 best IT certifications comes into play. While this list may not include the 10 best accreditations for you, it does catalog 10 IT certifications that possess significant value for a wide range of technology professionals(SONY VAIO PCG-5K1L battery).

#1: MCITP

The new-generation Microsoft Certified IT Professional credential, or MCITP for short, is likely to become the next big Microsoft certification. Available for a variety of fields of expertise — including database developer(SONY VAIO PCG-6W2L battery), database administrator, enterprise messaging administrator, and server administrator — an MCITP validates a professional’s proven job-role capabilities. Candidates must pass several Microsoft exams that track directly to their job role before earning the new designation(SONY VAIO PCG-7112L battery).

As with Microsoft’s other new-generation accreditations, the MCITP certification will retire when Microsoft suspends mainstream support for the platforms targeted within the MCITP exams. By matching the new certification to popular job roles(SONY VAIO PCG-8Z1L battery), as has been done to some extent with CompTIA’s Server+ (server administrator), Project+ (project manager), and A+ (desktop support) certifications, Microsoft has created a new certification that’s certain to prove timely, relevant, and valuable(SONY VAIO PCG-8Z2L battery).

#2: MCTS

The new-generation Microsoft Certified Technology Specialist (MCTS) helps IT staff validate skills in installing, maintaining, and troubleshooting a specific Microsoft technology. The MCTS certifications are designed to communicate the skills and expertise a holder possesses on a specific platform(SONY VAIO PCG-8Y2L battery).

For example, candidates won’t earn an MCTS on SQL Server 2008. Instead, they’ll earn an MCTS covering SQL Server business intelligence (MCTS: SQL Server 2008 Business Intelligence), database creation (MCTS: SQL Server 2008, Database Development), or SQL server administration (MCTS: SQL Server 2008, Implementation and Maintenance) (SONY VAIO PCG-8Y1L battery).

These new certifications require passing multiple, tightly targeted exams that focus on specific responsibilities on specific platforms. MCTS designations will expire when Microsoft suspends mainstream support for the corresponding platform. These changes, as with other new-generation Microsoft certifications, add value to the accreditation(SONY VAIO PCG-7Z2L battery).

#3: Security+

Security continues to be a critical topic. That’s not going to change. In fact, its importance is only going to grow. One of the quickest ways to lose shareholder value, client confidence, and sales is to suffer a data breach. And no self-respecting technology professional wants to be responsible for such a breach(SONY VAIO PCG-7Z1L battery).

CompTIA’s Security+ accreditation provides a respected, vendor-neutral foundation for industry staff (with at least two years of experience) seeking to demonstrate proficiency with security fundamentals(SONY VAIO PCG-7133L battery). While the Security+ accreditation consists of just a single exam, it could be argued that any IT employee charged with managing client data or other sensitive information should, at a minimum, possess this accreditation(SONY VAIO PCG-7113L battery). The importance of ensuring staff are properly educated as to systems security, network infrastructure, access control, auditing, and organizational security principles is simply too important to take for granted(SONY VAIO PCG-6W3L battery).

#4: MCPD

There’s more to information technology than just administration, support, and networking. Someone must create and maintain the applications and programs that power organizations. That’s where the new-generation Microsoft Certified Professional Developer (MCPD) credential comes into play(SONY VAIO PCG-7111L battery).

The MCPD accreditation measures a developer’s ability to build and maintain software solutions using Visual Studio 2008 and Microsoft .NET Framework 3.5. Split into three certification paths (Windows Developer 3.5, ASP.NET Developer 3.5, and Enterprise Applications Developer 3.5) (SONY VAIO PCG-6W1L battery), the credential targets IT professionals tasked with designing, optimizing, and operating those Microsoft technologies to fulfill business needs.

A redesigned certification aimed at better-measuring real-world skills and expertise, the MCPD will prove important for developers and programmers(SONY VAIO PCG-6V1L battery). Besides requiring candidates to pass several exams, the MCPD certification will retire when Microsoft suspends mainstream support for the corresponding platform. The change is designed to ensure the MCPD certification remains relevant, which is certain to further increase its value(SONY VAIO PCG-6S3L battery).

#5: CCNA

The Cisco Certified Internetwork Expert (CCIE) accreditation captures most of the networking company’s certification glory. But the Cisco Certified Network Associate (CCNA) might prove more realistic within many organizations(SONY VAIO PCG-6S2L battery).

In a world in which Microsoft and Linux administrators are also often expected to be networking experts, many companies don’t have the budgets necessary to train (or employ) a CCIE(SONY VAIO PCG-5J2L battery). But even small and midsize corporations can benefit from having their technology professionals earn basic proficiency administering Cisco equipment, as demonstrated by earning a CCNA accreditation(SONY VAIO PCG-5L1L battery).

As smaller companies become increasingly dependent upon remote access technologies, basic Cisco systems skills are bound to become more important. Although many smaller organizations will never have the complexity or workload necessary to keep a CCIE busy, Cisco’s CCNA is a strong accreditation for technology professionals with a few years’ experience seeking to grow and improve their networking skills(SONY VAIO PCG-5K2L battery).

#6: A+

Technology professionals with solid hardware and support skills are becoming tougher to find. There’s not much glory in digging elbow-deep into a desktop box or troubleshooting Windows boot errors. But those skills are essential to keeping companies running(SONY VAIO PCG-5J1L battery).

Adding CompTIA’s A+ certification to a resume tells hiring managers and department heads that you have proven support expertise. Whether an organization requires desktop installation, problem diagnosis, preventive maintenance(SONY VAIO PCG-5G3L battery), or computer or network error troubleshooting, many organizations have found A+-certified technicians to be more productive than their noncertified counterparts.

Changes to the A+ certification, which requires passing multiple exams, are aimed at keeping the popular credential relevant(SONY VAIO PCG-5G2L battery). Basic prerequisite requirements are now followed by testing that covers specific fields of expertise (such as IT, remote support, or depot technician). The accreditation is aimed at those working in desktop support, on help desks, and in the field, and while many of these staffers are new to the industry, the importance of an A+ certification should not be overlooked(SONY VGP-BPS13B/S Battery).

#7: PMP

Some accreditations gain value by targeting specific skills and expertise. The Project Management Professional (PMP) certification is a great example(SONY VGP-BPS13S Battery).

The Project Management Institute (PMI), a nonprofit organization that serves as a leading membership association for project management practitioners, maintains the PMP exam(SONY VGP-BPS13AS Battery). The certification measures a candidate’s project management expertise by validating skills and knowledge required to plan, execute, budget, and lead a technology project. Eligible candidates must have five years of project management experience or three years of project management experience and 35 hours of related education(SONY VGP-BPS13A/S Battery).

As organizations battle tough economic conditions, having proven project scheduling, budgeting, and management skills will only grow in importance. The PMI’s PMP credential is a perfect conduit for demonstrating that expertise on a resume(Sony VAIO VGN-FZ15G Battery).

#8: MCSE/MCSA

Even years after their introduction, Microsoft Certified Systems Engineer (MCSE) and Microsoft Certified Systems Administrator (MCSA) credentials remain valuable. But it’s important to avoid interpreting these accreditations as meaning the holders are all-knowing gurus, as that’s usually untrue(Sony VAIO VGN-FZ15T Battery).

In my mind, the MCSE and MCSA hold value because they demonstrate the holder’s capacity to complete a long and comprehensive education, training, and certification program requiring intensive study. Further, these certifications validate a wide range of relevant expertise (from client and server administration to security issues) on specific, widely used platforms(SONY VGP-BPS13/B Battery).

Also important is the fact that these certifications tend to indicate holders have been working within the technology field for a long time. There’s no substitute for actual hands-on experience(Dell N3010 Battery). Many MCSEs and MCSAs hold their certifications on Windows 2000 or Windows Server 2003 platforms, meaning they’ve been working within the industry for many years. While these certifications will be replaced by Microsoft’s new-generation credentials, they remain an important measure of foundational skills on Windows platforms(Dell INSPIRON 1764 battery).

#9: CISSP

As mentioned with the Security+ accreditation earlier, security is only going to grow in importance. Whatever an organization’s mission, product, or service, security is paramount(Dell INSPIRON 1564 battery).

(ISC)², which administers the Certified Information Systems Security Professional (CISSP) accreditation, has done well building a respected, vendor-neutral security certification. Designed for industry pros with at least five years of full-time experience, and accredited by the American National Standards Institute (ANSI) (Dell INSPIRON 1464 battery), the CISSP is internationally recognized for validating a candidate’s expertise with operations and network and physical security, as well as their ability to manage risk and understand legal compliance responsibilities and other security-related elements(Dell INSPIRON 1520 battery).

#10: Linux+

While pursuing my first Microsoft certification 10 years ago, I remember debating the importance of Linux with several telecommunications technicians. They mocked the investment I was making in learning Microsoft technologies. These techs were confident Linux was going to displace Windows(Dell INSPIRON 1420 battery).

Well, didn’t happen. Linux continues to make inroads, though. The open source alternative is an important platform. Those professionals who have Linux expertise and want to formalize that skill set will do well adding CompTIA’s Linux+ certification to their resumes(Dell INSPIRON E1505 battery).

The vendor-neutral exam, which validates basic Linux client and server skills, is designed for professionals with at least six to 12 months of hands-on Linux experience. In addition to being vendor-neutral, the exam is also distribution neutral (meaning the skills it covers work well whether a candidate is administering Red Hat, SUSE, or Ubuntu systems) (Dell INSPIRON 1525 battery).

Let the debate begin

Technology professionals almost always have strong reactions when debating certification’s value. Listing the top 10 certifications leaves room, of course, for only 10 credentials. That means many favorite and popular designations(SONY VGP-BPS13B/B Battery), such as HIPAA and Sarbanes-Oxley (SOX) certifications, have been necessarily omitted. Other important accreditations, including those for VoIP providers and from PC manufacturers, Red Hat, and even Apple, have also been left out here(SONY VGP-BPS13 Battery).

Which certifications would you leave off this list and which would you add in their place? Join the discussion and share the logic behind your choices(HP PAVILION DV6000 battery).

10 common backup mistakes

All of us in IT have been taught from Day One that performing regular backups is critical to an organization’s well being. Yet even seasoned pros sometimes make certain mistakes. Here are a few of the common mistakes I’ve encountered(Sony VGP-BPS13 battery).

1: Not making system state backups often enough

In Windows environments, system state backups have a shelf life. For domain controllers, the shelf life is equal to the maximum tombstone age (60 days by default). After that, the backup becomes null and void. Even for non domain controllers, the age of the backup is an issue(Sony Vaio VGN-FZ31M battery).

Each computer on a Windows network has a corresponding computer account in the Active Directory. Like a user account, the computer account has an associated password. The difference is that the password is assigned(Sony VGP-BPS13B/B battery), and periodically changed, by Windows. If you try to restore a system state backup that is too old, the computer account password that is stored in the backup will no longer match the password that is bound to the computer account in the Active Directory(Sony VGP-BPS13A/B battery), so the machine won’t be able to participate in the domain. There are workarounds, but it is usually easier to just make frequent system state backups of your servers(Sony VGP-BPS13/S battery).

2: Failing to adequately test backups

We all know that we should test our backups once in a while, but testing often seems to be one of those tasks that either falls by the wayside or that isn’t done thoroughly. Remember that making the backup is only the first step -if you can’t restore from them, you’re dead in the water. You need to ensure that those backups will work if and when you need them(Sony VGP-BPS13/B battery).

3: Not using an application-aware backup application

For some applications, a file-level backup is insufficient. A classic example of this is Microsoft Exchange, which requires an Exchange-aware backup application. Failure to use such a backup application causes the data that has been backed up to be in an inconsistent (and often unrestorable) state(Sony VGP-BPS13AS battery). It is therefore important to know which applications reside on your servers and to make note of any special application-specific backup requirements(Sony VGP-BPS13S battery).

4: Shipping backup tapes offsite too quickly

One of the companies I used to work for used a courier service to ship backup tapes offsite. Each morning at 8:00, the previous night’s backup tapes were transported to an offsite storage facility(Sony VGP-BPS13B/S battery). One morning, we had a server failure at about 9:30. Unfortunately, we couldn’t perform an immediate restoration because the tape had been shipped offsite. It was almost 4:00 before the tape could be located and returned to us(Sony VGP-BPS13A/S battery). By that time, the server had been down all day. While you should keep backups off site, consider waiting until the end of the business day to remove the previous night’s tapes from the building(SONY VAIO VGN-FZ31E Battery).

5: Having a single point of failure

Always remember that your backups are your safety net. If a server fails, your backups are the primary (and sometimes the only) mechanism for returning the server to a functional state(SONY VGP-BPS13 Battery). Because backups are so critically important, you should construct your backup architecture in a way that avoids (at least as much as possible) having a single point of failure. If possible, have a backup for your backups(SONY VGP-BPS13B/B Battery). You never want to find yourself in a situation in which you did not get a backup the night before and you are just praying that the server doesn’t fail that day because you have nothing to fall back on(SONY VGP-BPS13/B Battery).

6: Forgetting to plan for the future

Years ago, I managed the IT department for a large organization. While I was on vacation, some of my staff decided to surprise me by cleaning out a storage room that had become badly cluttered. In doing so, they threw out some obsolete computer equipment(SONY VGP-BPS13A/S Battery).

While this initially seemed harmless, some of the old equipment was in the storage room for a reason. Each quarter, the organization made a special backup that was kept as a permanent archive. Over time, though(SONY VGP-BPS13AS Battery), backup technology changed. Although the company had decided at one point to switch to a newer tape format, I had kept the organization’s old tape drives and an old computer that had a copy of the backup software installed on it, just in case we should ever have to read any of the data from an archive tape(SONY VGP-BPS13S Battery). The lesson to be learned is that although change is inevitable, you should always make sure that you have the necessary hardware and software to read your oldest backup tapes(SONY VGP-BPS13B/S Battery).

7: Not considering the consequences of using backup security mechanisms

For most organizations, IT security is a high priority. But sometimes, security can be a bad thing. I have seen real-world situations in which a backup could not be restored because nobody knew the password that had been used on the backup tape(SONY VAIO PCG-5G2L battery). I also once saw a situation in which an organization used hardware-level encryption and then upgraded to a new tape drive that didn’t support the previously used encryption (which meant that old backups could not be restored) (SONY VAIO PCG-5G3L battery).

There is no denying that it is important to secure your backups, but it is equally important to consider the consequences of your security measures. If you find yourself having to restore a backup after a major system failure, the last thing you need is an ill-conceived security mechanism standing in the way of the recovery(SONY VAIO PCG-5J1L battery).

8: Backing up only data

I once had someone tell me that I should be backing up only my data, as opposed to performing full backups that included the server’s operating system and applications. His rationale was that data-only backups complete more quickly and consume fewer tapes. While these are valid points, I completely disagree with the overall philosophy(SONY VAIO VGN-FZ31M Battery).

If an organization has a server failure and needs to perform a full recovery, it is usually possible to reinstall the operating system and the applications and then restore any data. However, time is of the essence when trying to recover from a crash(SONY VAIO VGN-FZ31J Battery). It is much faster to restore everything from backup than it is to manually install an operating system and a set of applications. More important, it is often difficult to manually configure a server so that it matches its pervious configuration(Sony Vaio VGN-FZ31S battery). Backing up the entire server ensures that its configuration will be exactly as it was before the crash.

9: Relying solely on a disk-to-disk backup solution

Disk-to-disk backup solutions offer many advantages over traditional tape backups. Even so, a disk-to-disk backup solution should not be an organization’s only backup, because the backup server is prone to the same risks as the servers it protects(SONY VAIO VGN-FZ31z Battery). A hurricane, lightning strike, fire, or flood could wipe out your backup server along with your other servers. For this reason, it is important to dump the contents of your disk based backups to tape on a frequent basis(SONY VAIO VGN-FZ38M Battery).

10: Using a tape rotation scheme that’s too short

One organization I worked for used a two-week tape rotation. This seemed to work fairly well, but we found out the hard way that two weeks just weren’t enough. The organization had an Exchange server fail because of corruption within the information store. When we tried to restore a backup, we found that we had backed up corrupt data(SONY VAIO VGN-FZ21m Battery). The corruption had existed for some time and had grown progressively worse. Every one of the backup tapes contained corrupt data, so the server could not be restored(SONY VAIO VGN-FZ11l Battery). This is a perfect argument for periodically testing your backups, but it also underscores the importance of using a long rotation scheme or at least keeping some of your backup tapes as long-term archives(SONY VAIO VGN-FZ11m Battery).