Solid State Disc Drives are the latest in memory technology, combining the speed and reliability of solid-state construction with the ability to store large volumes of data. Lifetime Memory's Solid State Drives (SSD's) provide robust performance and mission-critical reliability along with many other advantages:

• Fast Start-up and Access - no discs to spin or heads to move
• Low Power Consumption / Low Heat Production / Silent Operation
• Oustanding Durability - Shock / Vibration / Temperature Resistance

Hard Drive v. Solid State Drive

A solid-state drive (SSD) has no moving parts. By using transistors and solid-state components, SSD's offer ultra-fast access times. More specifically, inside an SSD are flash memory chips and a controller circuit. Without moving parts, an SSD doesn't need to start spinning and doesn't need to physically hunt data scattered across the drive. That’s what makes the SSD faster than a regular hard drive in nearly every way, so you have quick boot times, application launches, random writes and almost every other measure of drive performance (writing large files excepted).

Typically, a solid-state drive uses banks of NAND flash memory chips for storage — the same materials found in USB thumb drives. Flash memory is made up of "memory cells," which use transistors to store voltages. There are two basic types of flash memory - Single-Level Cells ("SLC") and Multi-Level Cells ("MLC"). Each offers advantages over the other, and both are being used in SSD technology. With single-level cell (SLC) memory, one bit of data is stored per cell. As a result, SLC memory is very fast and less prone to failure, but it is also expensive, so building a large SSD becomes quite costly. As a result, SLC memory is generally used for critical applications, like servers, where ultra-reliability and ultra-speed outweigh its costs. By contrast, multi-level cell memory is much more practical for normal use. Each cell can store up to 4 voltage levels, equivalent to two bits of data. This increases the density of storage and reduces costs, but operates slightly slower and tends to wear out over time. Even so, MLC SSD drives are so much more economical than SLC drives that they tend to dominate the market. For the time being most SSDs in general use are likely to be of the MLC variety.

Structurally, the flash memory within an SSD drive is divided into blocks, which are further broken down into pages. Unfortunately, while data can be read and written at the individual page level, it can only be erased at the block level. Suppose you have a 64K block and a 4K page, and you want to erase one page (1/16th of the data on the page). To do so, flash memory requires that you erase the whole block, and then write the rest of the data back to the block. This is a serious concern because MLC flash memory can wear out after approximately 10,000 write cycles. Moreover, as the drive fills up, performance drops, because, without free blocks to write to, the drive go through that intensive erase and rewrite cycle.

Flash Chips on an SSD

The first technique for extending flash-memory life is "wear leveling," which is simply writing to new areas of the drive instead of writing to the same memory over and over again. The goal is to fill up the entire drive with data before resorting to erasing blocks. Similarly, the issue of "Write amplification" where data is written and re-written to a drive by the operating system, is also being mitigated by shifting from block-level drive management to the page level. As more granular algorithms, with caching and prediction, are adopted,there's less unnecessary erasing and writing to the drive.

Another important advance in supporting SSD's is the implementation of the "TRIM" command. When the CPU sends a TRIM command to the drive, it lets the drive know which data blocks are no longer needed. With this information, the controller can clear that data making that space available for writing immediately, enabling the drive to work more quickly.

For anyone who wants their machine to work more quickly, SSD drives provide a real shot in the arm. Although they remain a little pricey, as economies of scale begin to decrease prices, SSD's are set to become a competitor and likely replacement for many traditional hard drives.