Interesting AMD64 comment (Slashdot)

In all seriousness, 64-bit computing by itself means that the General Purpose Registers are 64-bits wide. That means increased dynamic range. Using base 2, a 32-bit processor gives you 4,294,967,296 possible values. (which is where the 4 GB RAM limit of 32-bit processors comes from.) That is it’s dynamic range.

A 64-bit processor’s dynamic range is approximately 4.3 billion times greater than a 32-bit processor, which simply means, it can work with much larger numbers. Thats Important in applications like rendering, mathmatical calculations, and even database servers .

64-bit computing also allows for more RAM than a 32-bit processor because of it’s increased dynamic range. As shown, a 32-bit processor can only handle about 4.3 billion values, which roughly works out to about 4 GB of memory. A 64-bit processor has an upper limit of about 18 million terabytes… (32-bit = 0.0043 terabytes… 64-bit = 18,000,000 terabytes), something that I don’t see anyone quite needing, but it does mean that your 64bits will go further :)

AMD changed some more things when they designed the Athlon-64.

To start with they used a 40-bit memory address rather than 64-bit since we’re not going to need 18 million terabytes of memory anytime soon. Therefore a 40-bit address allows up to 1 terabyte of memory. Thats enough, considering that you won’t find a motherboard with support for 1024 sticks of 1GB ram anytime soon.

Then they doubled the amount of General Purpose Registers so there is now 16. So not only have we doubled the number of addresses, we then make them twice as big again. But they can only be used by 64-bit software, so the benefit of extra registers isn’t realized with 32-bit software, which is my point. A 32bit app isn’t going to excell on a 64bit processor, hence why benching it isn’t fair.

After that they lengthened the pipeline by a few stages. In short, you basically make it so higher clock speeds are easier to reach without having to change the format of the processor.

AMD have also built the memory controller into the core, which eliminates almost all latency issues from the CPU to the memory controller. Basically the memory is now just connected to the CPU by wires, whereas the CPU was connected to the northbridge, and so was the RAM. So the northbridge sat between the RAM and the CPU.

Then you have added support for SSE2, so applications designed to take advantage of Intel’s SSE2 instructions can now also take advantage of those instructions on an Athlon-64. So now Intel isn’t holding the upper hand again.

Finally they are using SOI, which in short, reduces current leakage within the processor, making switching of the transistors more efficent, which means faster speeds and less power consumption.

They’ve made other changes as well, quite alot more than listed here, but those are the main ones that effect performance.


One Response to “Interesting AMD64 comment (Slashdot)”

  1. NeoThermic says:

    Intresting. A comment that I make ends up on a webblog somewhere on the internet.
    Just for those that need the fill in, I was explaing the long and short of why a 64bit binary should be faster than a 32bit binary on a 64bit platform on a slashdot story (spcifically this story on slashdot)

    How I got here? I normally google random things when I’m bored, and decided to try my nick. And found this, how nice :)
    Glad you found it intresting.


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