What is RAM, DRAM, SRAM, and VRAM?

RAM (Random Access Memory) is basically a generic term for computer memory
that can hold different information as needed (as opposed to Read Only
Memory (ROM), which has information burned into the chips that cannot be
changed).  All these other types of memory are types of RAM.

DRAM is Dynamic RAM.  It is the bulk of the RAM in all systems today.  It
is the slowest and least expensive type of RAM.  Most systems today come
with 4-8MB or more.  The name Dynamic RAM comes from the fact that the
information in the DRAM will deteriorate and become useless. To keep this
from happening, the microprocessor has to periodically refresh the memory.

SRAM is Static RAM, or microprocessor cache RAM.  This RAM does not need to
be refreshed like DRAM, and because of this and some other design features
of SRAM, it is significantly faster than DRAM.  SRAM can be either built
into the microprocessor (internal) or on separate chips (external).  Well,
if SRAM is so much faster than DRAM, why not replace the DRAM in computers
with SRAM?  While this would provide quite a speed boost, it would provide
an even larger cost increase, because SRAM is not only several times faster
than DRAM, it is also several times more expensive.  This being the case,
small amounts (usually 128-256K) can provide a noticeable speed increase.
The Intel 486 line of microprocessors has 8K of internal SRAM cache built
into each chip.  The microprocessor uses the fast SRAM as a buffer between
the even faster CPU itself and the slow DRAM.  This is actually quite
similar to the way disk-caching programs such as Smart Drive use DRAM as a
buffer between the disk drives and your CPU.

VRAM is Video RAM.  It is actually quite similar to DRAM with 1 main
difference: it can be written to and read from at the same time.  This is
quite useful when the video processor on your video card can read the image
from VRAM and send it to the screen without having to wait for the CPU to
finish writing it.  Since this feature is of little use in other parts of
your computer, this RAM is used almost exclusively for high-end Video
cards.  Some computers (including pre-Aptiva PS/1's) use DRAM for video
memory to keep costs down (VRAM is more expensive than DRAM).

If you have any questions about this procedure, please post a note in the
appropriate topic or forum area. Be sure to include your DOS version and
your model number (i.e., 2155-G82).