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64 bits … memory sizes Processor word width has absolutely nothing to do with memory size. e.g. 8-bit processors regularly interface with 16-bit-wide memory b
by colanderman 13y ago
64 bits … memory sizes
Processor word width has absolutely nothing to do with memory size. e.g. 8-bit processors regularly interface with 16-bit-wide memory buses, and 64-bit processors often allow use of 32-bit-wide pointers.
What the word width does affect is how much data can be processed by each instruction. Certain algorithms benefit immensely from this (you can easily double throughput), but the code needs to be written to take advantage of this (or at least, not to squander the advantage), and needs to be compiled to use 64-bit-wide registers.
- deleted 13y ago[deleted]
- plorkyeran 13y ago32-bit Windows Server 2003 supports up to 64 GB (although SQL Server is probably the only application which can actually do anything useful with that).
- colanderman 13y agoBy that logic, 8-bit computers would only access 256 bytes of memory (which is definitely not true). On processors where the hardware word size is less than the useful size of memory, there generally is another means of extending the addressing range (either per-page bank addressing, or special pointer registers).
- pmelendez 13y ago> "Processor word width has absolutely nothing to do with memory size." Huh? How would you address high positions on your 8Gb memory with a 32 bits pointer that will overflow after 4Gb?
- plorkyeran 13y agoYou don't have to have all of your memory mapped into your address space at once.
- colanderman 13y agoIf your processor doesn't have special pointer registers, you can use banked memory. (e.g. the high bits are selected on a page-by-page basis by the OS, which understands 64-bit-wide pointers.) If the processor does have special pointer registers (e.g. 6502, 6809, 8086, AVR, etc.), you use those.