Short for “solid-state drive.” A type of storage device, with no moving parts and typically based on flash RAM, that emulates the function of a conventional hard drive as a data storage medium. Characteristics of SSDs include a small amount of DRAM, which is used as a cache (similar to the cache found in hard disks), and in some cases a power source to maintain storage when the device’s power is turned off (often a capacitor or battery).

Advantages of SSDs over conventional hard drives include:

• No spin-up time (faster starts)

• No moving parts (better reliability)
• Consistent read performance (location of data on drive is irrelevant)
• No physical latency (no read or write heads to physically move)
• Low power consumption
• Low heat generation
• Extreme shock, temperature, and vibration resistance
• Higher data density (smaller, lighter form factor)
• Low incidence of failure during read or write (better reliability)

At this writing, disadvantages compared to conventional hard drives include:

• Higher cost per gigabyte

• Smaller maximum capacities
• Slower write performance than read performance
• Some security issues with re-writing encrypted data
• Limited lifespan and number of write/read cycles
• Due to “wear leveling,” performance can degrade with on-going use

Expect these disadvantages to diminish radically as the technology continues to improve.