| Minimum Video Memory Requirements |
As you can see, to display only 16 colors at 1024x768 resolution would require
exactly 384K of RAM on the video card. Upping the color depth to 8 bits per pixel
results in 256 possible colors, and a memory requirement of 786432 bytes or 768K.
Since no video card can install that exact amount, you would have to install an actual
1M on the video card.
In order to use the higher resolution modes and greater numbers of colors in SVGA
cards, such cards will need more memory than the 256K found on a standard VGA adapter.
Table shows some of the requirements for SVGA cards based on resolution and
color depth.
|
| Display Adapter Minimum Memory Requirements |
| Resolution |
Color
Depth |
Colors |
Video |
bytes of
Memory |
| 640x480 |
4-bit |
16 |
256K |
153600 |
| 640x480 |
8-bit |
256 |
512K |
307200 |
| 640x480 |
16-bit |
65536 |
1M |
614400 |
| 640x480 |
24-bit |
16777216 |
1M |
921600 |
| 800x600 |
4-bit |
16 |
256K |
240000 |
| 800x600 |
8-bit |
256 |
512K |
480000 |
| 800x600 |
16-bit |
65536 |
1M |
960000 |
| 800x600 |
24-bit |
16777216 |
2M |
1440000 |
| 1024x768 |
4-bit |
16 |
512K |
393216 |
| 1024x768 |
8-bit |
256 |
1M |
786432 |
| 1024x768 |
16-bit |
65536 |
2M |
1572864 |
| 1024x768 |
24-bit |
16777216 |
4M |
2359296 |
| 1280x1024 |
4-bit |
16 |
1M |
655360 |
| 1280x1024 |
8-bit |
256 |
2M |
1310720 |
| 1280x1024 |
16-bit |
65536 |
4M |
2621440 |
| 1280x1024 |
24-bit |
16777216 |
4M |
3932160 |
| Six Popular Types Of Memory |
| Memory type | EDO | VRAM | WRAM | SDRAM | SGRAM | RDRAM |
| Max. throughput (MBps) | 400 | 400 | 960 | 800 | 800 | 600 |
| Dual - or single-ported | single | dual | dual | single | single | single |
| Typical Data Width | 64 | 64 | 64 | 64 | 64 | 8 |
| Speed (typical) | 50-60ns | 50-60ns | 50-60ns | 10-15ns | 8-10ns | 330MHz
clock speed |
| Video memory types |
- DRAM - Dynamic Ram was the earliest memory used for video cards and remained the most widely used type until late 1996 when it was largely replaced by the faster EDO Ram. Traditionally supplied in 4 megabit (512k) chips with a 16 bit interface. To get the maximum data transfer speed between a 64 bit controller and ram, four chips were needed, meaning 2Mb of memory.
- EDO - Extended Data Out Ram offered faster refresh rates and screen redraws and soon replaced the existing standard.
- VRAM - Video Ram was horrendously expensive and remained the province of graphic designers and CAD users. A special type of dual-ported DRAM Dual ported, it could be updated from the computer and refresh the screen at the same time. Favoured by Diamond.
- WRAM - Another dual ported ram, with additional hardware functions for screen manipulation within the chip. Favoured by Matrox
- SDRAM - Synchronous DRAM.
- SGRAM - SDRAM with additional graphics functions in hardware. Favoured by Matrox.
- M-DRAM - MOSYS DRAM. This is Dram organised in 'chunks' to increase bandwidth. Favoured by Tseng, amongst others.
- RD-RAM / DRDRam - Direct Rambus Dram uses a special interface with a low pin count, allowing for high speed and low cost. (Used for Nintendos Ultra 64)
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