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2011年3月15日火曜日

32bit v.s. 64 bit CPU

I was not perfectly sure about what the difference between a 32bit CPU and that of 64-bit.
But all things have cleared away.

There are two differences between them.

1. The maximum size of number that each CPU can deal with.
I found an interesting site:

The below explains quite well about the difference.

2. The maximum size of memory size that can be effectively used.
This is because of 1., I think.
Since the maximum number 32 bit can express is up to 2^32 ~ 4*10^9,
it makes no sense to mount more-than-4GB memory on PC with a 32bit CPU.
And you can effectively use 2^64 ~ 10^19 byte memory on 64bit machine, theoretically.
Notice that ONE address is assigned to memory by ONE byte.

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