General Schvantzkopf wrote:
>
>> If I understand this correctly now, this means that moving a floating
>> point number might be faster on 64 bit hardware (comparable in the other
>> attributes), because the datapaths might be wider then on 32 bit
>> hardware. But this is independent of the software, which means: Yes, I
>> can profit from this with the 32 bit OS as well if the difference is
>> there between the systems.
>> Since you write that the width depends on the particular CPU, I guess
>> that there are 32 bit CPU's with 64 bit wide datapaths as well?
>
> Yes there were 64 bit datapaths inside of 32 bit CPUs, certainly the
> floating point paths were. However the modern high performance CPUs are
> all 64 bit anyway so why would you care about the organization of the old
> 32 bit CPUs. The only modern 32 bit CPUs are aimed at the ultra low
> power/ very cheap end of the market. You wouldn't buy a Via C7 if your
> objective was performance, you buy a Via system because you want
> something that only uses a few watts or because you want a < $200 box to
> perform some basic task.
>
> I don't think there is any reason to run 32 bit Linux on a 64 bit CPU.

There is. I did some research when I got a 64bit board.

Basically, if you are manipulating large blocks of data the 64 bit
instruction and data fetches make the whole RAM twice as fast, even if
clocked at the same speed.

So operations on large bocks of data - especially bitmaps - are much faster.

However 64 bit programs are usually larger than 32 bit ones, as stuff
gets padded out to 64 bit boundaries more. And if your computer is not
processor bound, but - say - IO bound, it doesn't matter what you do
internally, if you can only access disks so fast.


Real time tests showed that graphic intensive and computation intensive
tasks were faster on a 64 bit chip. Other activities..like reading a
file and writing it to a different location, were slower. The actual
programs were slower to lad as well, being IIRC 15% larger or so on average.

In my case, with no graphics going on at all it made sense to stay 32
bit. The machine was about 6 tis faster anyway than my old one puerly
because it had SATA drive in it.

aso, the 64 bit machines need a bit more RAM. I only had 512mByte
(mainly apache SQL samba server, this box)

So I stuck with 32 bit: that way I didn't have top terad any bleeding
edge furrows, with possibly and undepecced machine for a 64 bit kernel.




> There is no downside to 64 bit Linux vs 32 bit Linux and there hasn't
> been for a long time. 64 bit Linux has been around for years, it's just
> as stable as 32 bit Linux, it has all of the same drivers, and it will
> run 32 bit applications just as well.

That is not what I found on the net. With some quite recent tests
showing that 64 bit was anything from 20% slower, and needing 30% more
resources,to up to 4 times faster, depending on what was being run.