Have to agree with Fruit Bat /\0/\ it depends on the motherboard. Older machines used to insist on it being done in pairs, newer machines do not insist on this unless it uses dual channel memory. If it does then you have to put in the memory in pairs as before. My PC built at Xmas gives the option to use either dual channel memory or normal memory depending on what slots you use. So I suppose the answer is you're both right depending on the machine.
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