question about 32 bit addresses??

This is a discussion on question about 32 bit addresses?? within the C++ Programming forums, part of the General Programming Boards category; Hi, I have a quick question, I am somewhat confused about this...but I keep reading about 32 bit -vs- 64 ...

  1. #1
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    question about 32 bit addresses??

    Hi,

    I have a quick question, I am somewhat confused about this...but I keep reading about 32 bit -vs- 64 bit computers.

    Does this mean that for example there are computers for which it can have addresses of 32 bits or maybe 64 bits...

    Is my understanding correct??

    THanks for any clarification!

  2. #2
    Master of the Universe! velius's Avatar
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    The 32bit memory model allows for 4294967296 Bytes of addressable memory. Therefore the 64bit memory model allows for 1.8844674407 x 10 ^ 19 Bytes of addressable memory. As you can see this is a significant increase. Which then means more IRQs DMAs and I/O Addresses. Alowing for more hardware installed at once. The processor also processes twice as much data per clock cycle.
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    The number of bits refers to the data bus.

    A 64-bit processor has a 64 bit data bus. The data bus, accumulator(s), & registers are 64 bits (8 bytes) wide. Most processors will have address busses that are wider than their data busses. For example most of the old 8-bit processors had 16 address bits. At least one of the "new" 64 bit processors has a 48-bit address bus... I don't remember which one.
    Last edited by DougDbug; 09-12-2003 at 12:42 PM.

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    How many bits a processor has is largely a marketing term. I would say a processor is 64 bits if it has a 64 bit adressing mode (there may not be 64 addressing lines as Doug mentioned) And if those 64 bits can fit into a single register. If the integer registers are also 64 bits then it's a "real" 64-bit processor. The general trend has been for much wider data busses than address for some time the original Pentium "Classic" had a 64 bit data bus, as does the Athlon. The NForce2 motherboard has a 128 bit data bus, it just looks like 64 bits to the chip. From C, if sizeof(void *) and sizeof(size_t) is both 8, then you are in 64 bit mode. int's and long's almost never seem to get promoted, though this was the key difference between 16 and 32 bit machines. Too many people assumed sizeof(int) == sizeof(long) == 4

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