当你在电脑上添加RAM时，如果记忆棒的内存不相等，或者你总是需要它们的内存相等，这真的很重要吗？今天的超级用户问答帖子回答了一位好奇的读者的问题。

今天的问答环节是由SuperUser提供的，SuperUser是Stack Exchange的一个分支，是一个由社区驱动的问答网站分组。

图片由redjar（Flickr）提供。

问题

超级用户读者LanceLafontaine想知道使用不同数量的RAM是否真的会降低性能：

This page describes the RAM specificati*** for many of the MacBook laptops. In the section for my laptop (13″ Pro, Late 2011), it says:

• Additional Notes: For best performance, fill both memory slots, installing an equal memory module in each slot.

This is not the first time that I have heard of this phenomenon, and it is definitely not specific to Apple. Why is this the case? Other than the obvious decrease in available memory, why would it be worse to run with 6 GB (1*4 GB plus 1*2 GB) than with 8 GB (2*4 GB)?

使用不同数量的RAM会导致性能下降吗？还是仅仅是一个神话？

答案

超级用户贡献者davidschwartz和x为我们提供了答案。首先，大卫·施瓦茨：

With equal amounts of memory in both slots, memory can be interleaved so that successive chunks of memory alternate slots. That way, memory access gets distributed to both slots almost perfectly evenly, allowing their bandwidth to combine.

With uneven amounts, memory cannot be interleaved and has to be mapped first to one stick and then the other. A program that is accessing a large contiguous chunk of memory will find almost all of its access going to one stick and there will be no bandwidth combination.

接着是mVincent的回答：

• Additional Notes: For best performance, fill both memory slots, installing an equal memory module in each slot.

The likely technical explanation here is that your MacBook (motherboard) supports dual-channel architecture and thus requires two identical memory modules. Benchmarks suggests that it gives a 5-10 percent performance boost.

• Why is this the case? Other than the obvious decrease in available memory, why would it be worse to run with 6 GB (1*4 GB plus 1*2 GB) than with 8 GB (2*4 GB)?

When two non-identical memory modules are used, the motherboard will run the memory modules at the speed of slowest module.

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