Hardware Reference
In-Depth Information
backlash against proprietary formats, Olympus and Fujifilm abandoned xD-Picture card
in 2010.
SSD (Solid-State Drive)
In general, a
solid-state drive (SSD)
is any drive using solid-state electronics (that is, no
mechanical parts or vacuum tubes). Many people believe that SSDs are a recent advance-
ment in computer technology, but in actuality they have been around in one form or an-
other since the 1950s, well before PCs even existed.
Virtual SSD (RAMdisk)
Although most people think of a physical drive when they discuss SSDs, these drives
are available in both physical and virtual form. A virtual SSD is traditionally called a
RAMdisk because it uses a portion of system RAM to act as a disk drive. The benefits are
incredible read/write performance (it is RAM, after all), whereas the drawbacks are the
fact that all data is lost when the system powers down or reboots, and that the RAM used
for the RAMdisk is unavailable for the operating system (OS) and applications.
RAMdisk software has been available for PCs since right after the PC debuted in late
1981. IBM included the source code to a RAMdisk program (later called VDISK.SYS)
in the March 1983 PC DOS 2.0 manual, as part of a tutorial for writing device drivers.
(Device driver support was first implemented in DOS 2.0.) IBM later released
VDISK.SYS as part of PC DOS 3.0 in August 1984. Microsoft first included a RAMdisk
program (called RAMDRIVE.SYS) with MS-DOS 3.2 (released in 1986). Versions of
RAMDRIVE.SYS were included in DOS and Windows versions up to Windows 3.1, and
a renamed version called RAMDISK.SYS has been included with Windows XP and Win-
dows 7/Vista. However, they are not automatically installed, and they are not well docu-
mented. These DOS- or Windows-based RAMdisk programs are useful for creating high-
speed SSDs using existing RAM.
Flash-Based SSDs
ShortlyafterthereleaseoftheIBMPCin1981,severalcompaniesdevelopedandreleased
physical solid-state drives that could function as direct hard drive replacements. Many
of these used conventional dynamic or static RAM, with an optional battery for backup
power, whereas others used more exotic forms of nonvolatile memory, thus requiring no
power to retain data. For example, Intel had released “bubble” memory in the late 1970s,
which was used in several SSD products. Bubble memory was even included in the Grid
Compass in 1982, one of the first laptops ever released. Although SSDs can use any type
of memory technology, when people think of modern SSDs, they think of those using
flash memory. Flash-based SSDs more recently started appearing in commercially avail-
