[X4U] 64 vs 32 was...Re: move to Intel

[Bill Northcott]

On 16/06/2005, at 12:08 AM, Richard Gilmore wrote:
>
> That's what I mean one's 32 bit and the other 64 but if the "bits"  
> don't
> matter and 64s are actually slower why's my iMac G5 faster?

>> On 12/6/05 3:29 PM, "David Ledger" <dledger at ivdcs.demon.co.uk> wrote:
>
>> 64 bit machines are usually slower than their 32 bit counterparts,
>> but they handle huge dataspaces. If you don't use > 4GB address space
>> you don't gain anything, but all those extra bits have to
>> sucked/squirted serially from and two the disc and other devices.

This is nothing to do with 64 vs 32 bits.  The G5 is much more  
powerful 32 bit chip clock for clock than the G4.
The memory bus on the G4 runs at 167MHz, even a 1.8GHz G5 has a  
667MHz memory bus (the fastest 2.7GHz G5s are twice that bus speed),  
but because the bus is more efficient, the actual memory bandwidth  
improvement is more than the 4x clock would suggest.  Also as soon as  
you have any floating point math, the G5 has two FPUs vs only one in  
the G4.

Bill Northcott