IBM 64/256KB Memory Expansion Option - Examples
IBM 5150: 64-256KB motherboard
Fully RAM populated - being topped up to 640 KB
IBM 5160: 64-256KB motherboard
Partially RAM populated - being topped up to 640 KB
Fully RAM populated - being topped up to 640 KB
IBM 5160: 256-640KB motherboard
Partially RAM populated - being topped up to 640 KB ( Unlikely scenario. Most people would populate the motherboard. )