31 Should I get 1 MB or 2 MB of video memory?
Description
This article is from the comp.sys.ibm.pc.hardware.video Frequently Asked Questions, by Michael Scott with numerous contributions by others. (v1.0).
31 Should I get 1 MB or 2 MB of video memory?
To determine the amount of video RAM you will need, use the method outlined in "How do I calculate how much VRAM/DRAM I need?"
There is another issue which is important to consider if the video card in question is a 64 bit card or is 32 bit but uses memory interleaving. Standard DRAM is addressed 32 bits at a time and typically one 1 MB bank is 32 bits wide and 256 kbytes deep, so if 2 1 MB banks are installed, each can be addressed separately. In practice, a 64 bit video controller can move 64 bits in or out of video RAM in each clock cycle, 32 bits to/from each bank. If only one bank of DRAM is installed (i.e. 1 MB) then the effective bandwidth of the card is halved. In a similar fashion, a 32 bit controller that supports memory interleaving like the ET4000W32i/p can move twice as much data per clock cycle if it has 2 MB of DRAM installed (see "How does memory interleaving work to increase the speed of a video card?" This means that 64 bit cards that have only 1 MB of video RAM will operate much more slowly that if a full 2 MB is installed. This may result in lower refresh rates and more sluggish performance.
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