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Glossary of memory acronyms
Published on 9/21/97 This Netpanel special feature will
define and explain a wide variety of acronyms dealing with RAM, or simply memory
as most people call it. The acronyms we present are in a fairly logical order, so it
shouldn't be too difficult to find what you're looking for.
- RAM (Random Access Memory)
This is the basic form of computer memory, which can be accessed randomly. In other words,
data can be read from or written to any byte of RAM, regardless of its position.
- SIMM (Single Inline Memory Module)
A small circuit board holding a bank of memory chips. Generally, Macintosh SIMMs hold 8
chips, while PC SIMMs hold 9; the ninth chip being for parity error checking. The 72-pin
SIMMs that are common today must be added to a Pentium-based motherboard in matched pairs,
to compensate for their 32-bit data path.
- DIMM (Dual Inline Memory Module)
A small circuit board holding a bank of memory chips, with different contacts on each
side, allowing for twice the number of pins as a SIMM. This gives the Pentium its required
64-bit data path to the memory, eliminating the need to add DIMMs in matched pairs.
- DRAM (Dynamic Random Access Memory)
This is the type of memory that is most widely used in PCs. DRAM must be continually
refreshed or it will lose its state (on/off), making it slower than SRAM.
- SRAM (Static Random Access Memory)
This type of memory is faster and more reliable than DRAM because it needs to be refreshed
less often, but it is more expensive and requires more power.
- FPM DRAM (Fast Page Mode Dynamic Random Access Memory)
This type of memory is slightly faster than DRAM. It allows for a burst cycle, which
increases the speed of subsequent accesses to the memory after the initial read. FPM DRAM
is generally being replaced by EDO DRAM.
- EDO DRAM (Extended Data Out Dynamic Random Access Memory)
This type of memory has an internal cache, which allows for an entire block of memory to
be read at once. This gives the processor more time to retrieve the data, increasing
access speeds. This type of transfer is called a pipeline burst. EDO DRAM is only slightly
more expensive than conventional DRAM.
- BEDO DRAM (Burst Extended Data Out Dynamic Random Access Memory)
This type of memory is slightly faster than EDO DRAM, because it allows the processor to
read data each clock cycle. However, many motherboards do not support BEDO DRAM, and it is
generally being passed up for SDRAM.
- SDRAM (Synchronous Dynamic Random Access Memory)
This type of memory brings about yet another speed improvement: it can be clocked at
higher speeds than BEDO DRAM. SDRAM synchronizes itself with the processor to match bus
speeds, but only up to about 100 MHz.
- RDRAM (Rambus Dynamic Random Access Memory)
This type of memory can deliver data at speeds of up to 600 MHz. Currently, RDRAM is only
used in certain high-performance graphics workstations, and it is also used in the
Nintendo64. Intel is licensing RDRAM technology for its future motherboards, but this type
of memory requires a special motherboard architecture.
- SLDRAM (SyncLink Dynamic Random Access Memory)
This type of memory is being developed as an alternative to RDRAM, but it currently only
exists on paper.
- VRAM (Video Random Access Memory)
This type of memory is used on video adapters, and is dual-ported, meaning that it can be
accessed by two devices simultaneously. This allows the monitor to access the memory for
screen updates, while at the same time allowing the graphics processor to provide new
data.
- WRAM (Window Random Access Memory)
This type of dual-ported memory is very similar to VRAM, and is used for the same purpose.
WRAM, however, is faster and less expensive.
- SGRAM (Synchronous Graphic Random Access Memory)
This type of memory can be considered a graphics-optimized version of SDRAM, in that it
too is synchronized with the system bus. SGRAM, however, uses certain techniques to
provide more bandwidth to graphics-intensive operations.
- NVRAM (Non-Volatile Random Access Memory)
Any type of memory that is made non-volatile by connecting it to a constant power source,
such as a battery. Therefore, non-volatile memory does not lose its contents when the main
power is turned off.
- PRAM (Parameter Random Access Memory)
This type of memory is found in Macintosh computers, and powered by a battery. It is used
to store system configurations, as well as the date and time, even when the machine is
turned off.
- ECC (Error-Correcting Code)
This is a technique used in some types of memory to check the accuracy of the data it
stores. This is generally accomplished using a checksum method.
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