Solid-State Disk.
From Webopedia.com:
<< Solid State Disks (SSD) are high performance plug-and-play storage devices that contain no moving parts. SSD components include either DRAM or EEPROM memory boards, a memory bus board, a CPU, and a battery card.
Because they contain their own CPUs to manage data storage, they are a lot faster (18MBps for SCSI-II and 35 MBps for UltraWide SCSI interfaces) than conventional rotating hard disks ; therefore, they produce highest possible I/O rates.
SSDs are most effective for server applications and server systems, where I/O response time is crucial. Data stored on SSDs should include anything that creates bottlenecks, such as databases, swap files, library and index files, and authorization and login information. >>