Re: [Nolug] Centos

From: Ron Johnson <>
Date: Thu, 27 Oct 2011 01:43:58 -0500
Message-ID: <>

On 10/27/2011 12:36 AM, Jimmy Hess wrote:
> On Thu, Oct 27, 2011 at 12:18 AM, Ron Johnson<> wrote:
> [snip]
>> You seems to be confusing modern CPUs with the 8088 or 80386SX (which most
>> here will remember had data busses half of the register width), since a
>> 64-bit data bus moves 64 bits from cache just as fast as it moves 32 bits.
> It's true that it moves bits from the cache just as fast,
> but I'm sure you're missing something here...
> 256k of SRAM holds half as many long mode instructions as short mode
> instructions that can be held in that same amount of cache, because
> more bits of the cache are consumed by a larger operand.
> There are instructions that have data dependencies on bits in the
> operand, for example SBB, these are not simple transforms based on
> corresponding bits in the two or three operands, there are more
> logical "steps" for each bit.
> Width of the bus is important, but only one factor

Another factor is the number of registers: the more there are the less
you need to shuffle stuff back and forth to RAM.

Completely unobvious, supposedly io-bound stuff like populating a Gtk
chooser window of a directory with 45,000 files in it is markedly faster
in 64 bits.

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