[clue-tech] 64-bit software use

[dperkins at frii.com]

>>
>>> Most of my computer use is for web-browsing, email, writing, and some
>>> small programming and databasing. Would it benefit me to run a 64-bit
>>> OS
>>> and software? I am currently using Fedora Core 5, and would continue to
>>> do so in its 64-bit version.
>
> I had heard that when using a 64 bit OS, you need twice the memory just to
> run the same programs. But I'm having trouble verifying that.
>
> Other than that, the only benefit I know of is that the 64bit OSes can use
> more than 4GB of memory. Not a big deal for a laptop.
>
> So, I wouldn't do it unless you had a specific reason for using it.
>
> Erik Z

It's hard to quantify how much more memory a 64-bit program, or any
program, will need.  The x86 instruction size varies from one byte to a
few bytes and only instructions containing addresses or offsets could
potentially grow in size.  Most variables and constants will probably jump
from 32 bits to 64 bits in size, unless they are strings or characters. 
Some are local variables and are stored on the stack, so most of them can
probably be ignored since they disappear when the subroutine ends. 
Programs usually ask the OS for more memory, and depending on the program,
that amount could easily double.

I suspect that the increase in program size for a RISC processor like the
PPC might be greater since their instructions tend to be word aligned and
word sized, but I don't know how they have handled going from 32 to 64
bits.


The variable size of x86 instructions can make it easier to keep the
pipeline full, altho grabbing 64-bit data can offset that. A 64-bit CPU
can also grab data twice as fast, so you will see benefits there.  But
when browsing the web, doing email, writing a document, the CPU spends
most of its time loafing.  If there is a delay, it's probably due to
external factors, such as the Internet connection. Or the speed of the
hard drive.