🚀 go-pugleaf

msmith@jolt.mpx.com.au (Michael Smith) wrote:

> Very few people (who I know anyway) buy 64 bit machines to address more 
> than 4GB of memory.  They do it to get faster throughput.  The extra 
> address space is simply a side-effect.  While increasing your bus from 32 
> to 64 bits may increase your address space by an enormous amount, it only 
> increases the throughput by a factor of 2.  I can easily imagine users 
> (in the next few years) wanting 128 bit graphics cards, disk controllers 
> and network interface cards and thus wanting a 128 bit bus.

  You seem to be confusing the address bus with the data bus. An
_address_ bus of 64 bits does not increase throughput at all. I can
think of no compelling reason for a 64-bit address bus, but I may feel
differently in a few years. A 64-bit _data_ bus, on the other hand,
_does_ double the throughput when compared to a 32-bit bus. This is
exacly why a Pentium, for example, has a 64-bit external data bus,
even though it has only 32-bit registers. (Note that here the address
bus and the data bus have different size).

  I guess that what all this proves is that the phrase "64-bit
machine" is nonsensical. 64-Bit by what definition? External or
internal bus, data or address, register size? Without this
information, "64-bit machine" tells you _nothing_.

  Gertjan.

-- 
Gertjan Klein   <gklein@xs4all.nl>