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random-access memory
<storage> (RAM) (Previously "direct-access memory"). A data
storage device for which the order of access to different
locations does not affect the speed of access. This is in
contrast to, say, a magnetic disk, magnetic tape or a
mercury delay line where it is very much quicker to access
data sequentially because accessing a non-sequential location
requires physical movement of the storage medium rather than
just electronic switching.
The most common form of RAM in use today is built from
semiconductor integrated circuits, which can be either
static (SRAM) or dynamic (DRAM). In the 1970s magnetic
core memory was used. RAM is still referred to as core by
some old-timers.
The term "RAM" has gained the additional meaning of
read-write. Most kinds of semiconductor read-only memory
(ROM) are actually "random access" in the above sense but are
never referred to as RAM. Furthermore, memory referred to as
RAM can usually be read and written equally quickly
(approximately), in contrast to the various kinds of
programmable read-only memory. Finally, RAM is usually
volatile though non-volatile random-access memory is also
used.
Interestingly, some DRAM devices are not truly random access
because various kinds of "page mode" or "column mode" mean
that sequential access is faster than random access.
(1995-12-05)
Try this search on OneLook / Google
Nearby terms:
RAMIS II « RAMTRON « random « random-access memory » Random Access Memory Digital-to-Analog Converter » randomness » random numbers
Random Access Memory Digital-to-Analog Converter
<hardware> (RAMDAC) A combination of three fast DACs with a
small SRAM used in graphics display adapters to store the
colour palette and to generate the analog signals to drive a
colour monitor. The logical colour number from the display
memory is fed into the address inputs of the SRAM to select a
palette entry to appear on the output of the SRAM. This entry
is composed of three separate values corresponding to the
three components (red, green, and blue) of the desired
physical colour. Each component value is fed to a separate
DAC, whose analog output goes to the monitor, and ultimately
to one of its three electron guns (or equivalent in
non-CRT displays).
DAC word lengths range usually from 6 to 10 bits. The SRAM's
wordlength is three times the DAC's word length. The SRAM
acts as a colour lookup table. It usually has 256 entries
(and thus an 8-bit address). If the DAC's word length is also
8 bits, we have a 256 x 24-bit SRAM which allows a selection
of 256 out of 16777216 possible colours for the display. The
contents of the SRAM can be changed while the display is not
active (during display blanking times). The SRAM can
usually be bypassed and the DACs can be fed directly by
display data (for true colour modes).
(1996-03-24)
Try this search on OneLook / Google
Nearby terms:
RAMTRON « random « random-access memory « Random Access Memory Digital-to-Analog Converter » randomness » random numbers » random testing
This article was derived from the Free Online Dictionary of Computers and is available under ther terms of the GNU Free Documentation License.
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