question about GHZ

Strider590

InsideInsurance wrote: »

Just like computers, what you actually get will depend on more factors of how they've been joined together and what you are asking them to do. Its not as simple as saying either a 400mph car or a 200mph car

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If I really went into detail i'd be talking about 32 v 64 bit, front side bus speeds and CPU multipliers. I'd be explaining how 64 bit refers to the number of bits the CPU handle per "tick" or clock pulse and how this means that (in theory at least) a 64 bit CPU is twice as fast as a 32, but none of this helps the OP to understand the answer to the question they are asking.

Whereas making an everyday comparison does......

InsideInsurance

Strider590 wrote: »

.........

If I really went into detail i'd be talking about 32 v 64 bit, front side bus speeds and CPU multipliers. I'd be explaining how 64 bit refers to the number of bits the CPU handle per "tick" or clock pulse and how this means that (in theory at least) a 64 bit CPU is twice as fast as a 32, but none of this helps the OP to understand the answer to the question they are asking.

Whereas making an everyday comparison does......

Analogies are a good way to explain technical subjects but they have to be roughly accurate to work - both in the simplistic view and in the comparison.

Arguably the analogy itself was ok, the conclusion however was inaccurate and was not a parallel to the conclusion of the complex subject you were trying to explain

spud17

Strider590 wrote: »

.........

I'd be explaining how 64 bit refers to the number of bits the CPU handle per "tick" or clock pulse and how this means that (in theory at least) a 64 bit CPU is twice as fast as a 32,

And there was me thinking 32 bit was 2^32, roughly 4 Gibibytes of addressable memory, while 64 bit is 2^64 or around 16 Exbibytes of addressable memory.

33 bit (if there was such a thing in computing) would be twice the value of 32 bit.

securityguy

spud17 wrote: »

And there was me thinking 32 bit was 2^32, roughly 4 Gibibytes of addressable memory, while 64 bit is 2^64 or around 16 Exbibytes of addressable memory.

33 bit (if there was such a thing in computing) would be twice the value of 32 bit.

You're both right.

If you need to compare two 128 bit quantities for equality (say, you want to determine whether an IPv6 address is local or not) then a 64 bit machine will do it, all other things being equal, twice as fast as a 32 bit machine. The 64 bit machine will need four loads and two compares, the 32 bit machine will need eight loads and four compares. In reality, on a modern scalar architecture, the difference is much less because of the effects of pipelining, but the general argument holds.

The 64 bit machine will be able to address 2^32 times more memory (or, more to the point, will be able to deal with virtual address spaces 2^32 times larger) than a 32 bit machine, because addressable memory scales as to 2^n, where n is the width of the bus. But that doesn't make the 64 bit machine 2^32 times faster.