The only way to differentiate VRAM SIMMs is by the number of individual chips on the SIMM itself. The 256K VRAM SIMM has two (2) 40-pin ICs, and the 512K VRAM SIMM has 4 (four) 28-pin ICs.
Do keep in mind that VRAM SIMMs comes in two different speeds, 80ns and 100ns.
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