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What a Solid-state Drive (SSD) is…

A solid-state drive is a data storage device that uses solid-state memory to store persistent data. Unlike flash-based memory cards, an SSD emulates a hard disk drive, thus easily replacing it in most applications. There are two kinds of SSDs: flash-memory based ones and SRAM or DRAM based ones (often called RAM-drives). The RAM-drives data persistence can only be guaranteed thanks to a battery, but for a limited time.

It’s called solid-state drive because it uses semiconductor devices, and it doesn’t have any moving parts, unlike hard disk drives which consist of a motor, rotating platters with magnetic surfaces, and mobile read/write heads.

- left: hard disk drive. center & right: solid-state drive from above & under -

Comparison with hard disk drives:

+ Faster start-up (no mechanical delays);
+ Fast random access for reading (no read/write heads to move);
+ Low read/write latency times;
+ No noise (no mechanical movements), except for some high-capacity models which have cooling fans;
+ High mechanical reliability (no moving parts);
+ File fragmentation has almost no impact on performance, since the seek time is almost constant and is not dependent on the physical location of the data;
+ For low capacity SSDs, lower power consumption and heat production;
+ For low capacity SSDs, lower height and size.
- Price (as of mid-2008, around USD 3.50 per GB for flash memory, and around USD 0.40 per GB for mechanical drives);
- Capacity (currently far lower than that of usual hard drives, but predicted to swiftly increase, with experimental SSDs of up to 1 TB);
- High vulnerability to certain effects, such as abrupt power loss, magnetic fields, electric/static charges…..
- Limited write cycles (but the problem is improved all the time. Today’s SSDs can last up to 20 years with average usage). SSDs based on DRAM do not suffer from this problem;
- Slower write speeds (except for SSDs based on DRAM);
- Lower storage density (but is expected to rapidly increase in the near future);
- Higher power consumption (SSDs also take more power per GB).

The advantages of SSDs are interesting for mobile computing and are becoming increasingly popular in markets such as notebook PCs, Ultra-Mobile PCs, and electronics sectors. The capacity currently varies from 12GB to 256 GB. Decreasing prices in raw flash material costs, and in the mean time increasing capacities make SSDs tend to be the next hard disk drive generation.

More information on Wikipedia: http://en.wikipedia.org/wiki/Solid-state_drive