What is a Solid State Disk?

R. Kayne

A solid state disk (SSD) is a memory storage device without moving parts that can be used in place of a traditional hard disk. There are several advantages to a solid state disk and only one real disadvantage: cost. However, as costs continue to fall, experts predict solid state disks will replace platter-driven disks in many applications by 2009.

MP3 players utilize solid state disks for storage.
MP3 players utilize solid state disks for storage.

A solid state disk is made of memory chips and is both flash-based and non-volatile. Flash-based means that it uses flash technology to erase blocks of memory before writing to them. Therefore, solid state disks are also called flash drives. Non-volatile means that the disk does not require power to hold its contents. In other words, data is not lost when power is cut.


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There are many advantages to a solid state disk. It is far faster than a traditional hard disk, more rugged, can endure wider temperature fluctuations in the environment, does not heat up, is totally silent, is lighter, and uses very little power. All of these features combine to make the solid state disk ideal for portable keydrives or memory sticks, cell phones, PDAs, and other small devices.

As manufacturing costs fall, the solid state disk is also slated to become the disk of choice for laptops. Solid state laptops would be faster and lighter, with a significant increase in battery life. These larger solid state drives are sometimes called NAND (Not And) drives, versus the smaller NOR (Not Or) drives used in cell phones, PDAs, and other devices. NAND and NOR specify differing architectures relating to how the disks erase, read and write.

Solid state disks have limited lives based on erase cycles. The first devices had about one million erase cycles before failing. Some later technologies have introduced built-in routines that extend life by tracking cell usage in order to map data to lesser-used cells. This allows the device to see a full life cycle by wearing evenly. Otherwise, data written to the same cells over and over can lead to premature failure.

While the solid state disk is more expensive than a traditional hard disk, it is also highly portable and much more flexible. Keydrives, digital cameras and camcorders, MP3 players, cell phones, PDAs, and an array of other digital devices have revolutionized personal electronics with the help of the solid state disk.

Two flash memory chips.
Two flash memory chips.

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