For a 1024 × 768 resolution using 16-bit color, the calculation is as follows:1024 * 768 = 786,432 (pixels of resolution)
16 / 8 = 2 (color depth in bytes)
2 * 2 + 2 = 6 (buffers required in bytes)
786,432 * 6 = 4,718,592 (video RAM required for 3D graphics)The result of this calculation is a video card with 4MB of video RAM (even if it is a 3D
card)cannotsupporta3Ddisplaysettingof1024×768resolutionusing16-bitcolordepth
without adding additional video RAM.Video RAM Technologies
The video card’s memory is also called the frame buffer because it holds the graphic
instructions that define each frame before it is processed by the setup phase and
RAMDAC. The earliest video RAM was standard DRAM, which requires constant elec-
trical refreshing to hold its contents. DRAM didn’t work well for video RAM because it
cannotbeaccessedwhileitisbeingrefreshed,whichmeantvideoperformancesuffered.
A variety of memory technologies have been and are being used as video RAM on
videocards.ThemostcommonRAMtechnologiesusedwithvideocardsarethefollowing: Dynamic Random Access Memory (DRAM) This is the same RAM used on
early PCs. EDO DRAM has largely replaced DRAM on the PC, but other types
of video RAM are in use.
Extended Data Output DRAM (EDO DRAM) EDO DRAM provides a higher
bandwidth than standard DRAM and manages read/write cycles more efficiently.
Video RAM (VRAM) VRAM, not to be confused with the generic termvideo
RAM, is dual-ported, which means it can be written to and read from at the same
time. VRAM, which is a special type of DRAM, doesn’t need to be refreshed as
often as standard DRAM.
Windows RAM (WRAM) The video RAM used on Matrox video cards. It is
dual-ported and runs a bit faster than VRAM.
Synchronous DRAM (SDRAM) SDRAM is very much like EDO DRAM,
except that it is synchronized to the video card’s GPU and chipset, which
allows it to run faster. SDRAM is a single-ported memory technology that
is very common on video cards.
Multibank DRAM (MDRAM) MDRAM is a newer memory type that is
divided into 32KB banks, which can be accessed independently. MDRAM also
offers the advantages of interleaving, true memory sizing, and better memory
performance. Interleaving allows memory accesses to overall memory banks.
MDRAM can be sized exactly to the amount of video RAM needed to support
a particular display type.(^266) PC Hardware: A Beginner’s Guide