MadSci Network: Computer Science
Query:

Re: What are the advantages of 64-bit microprocessors over 32-bit?

Date: Sun Nov 21 03:50:34 2004
Posted By: Aaron Endelman, Sr. Software Engineer
Area of science: Computer Science
ID: 1100851506.Cs
Message:

During the past 30+ years, processor word size has increased from 4 to 8 to 16 to 32 to 64 bits. The benefits have been:

(1) increased address space
(2) increased number of instructions available
(3) greater arithmetic precision per execution cycle
(4) more data can be handled per execution cycle

Let’s look at how each of these benefits are affected by the 32-to-64 bit transition:

(1) The address space of an n-bit word is is 2n words, so the progression has been 16 → 256 → 32768 → ~4.3 x 109 → ~1.8 x 1019 words. So there's a huge increase in address size from 16 to 32 bits, which takes care of the needs of the vast majority of programs. 64 bits pretty much takes care of the needs of the remainder for the conceivable future.

(2) Modern instruction sets comprise typically a few dozen or at most a few hundred instructions, so we can see that a word size > 16 bits makes no difference in the number of possible instructions.

(3) Above 32 bits (9 decimal places of accuracy), calculations are most typically performed in scientific notation, although some calculations, notably encryption/decryption, are greatly aided by ever-increasing word size.

(4) Some operations on strings of characters can be performed with fewer memory accesses – half as many at 64 bits than at 32, thus executing in about half the time.

I think it’s safe to conclude that while 64-bit processors offer advantages over 32-bit processors, the advantages gained in the 16-bit to 32-bit transition have been far more significant.


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