On 20 Jan 2003 at 3:52, Ron Johnson wrote:
> On Mon, 2003-01-20 at 00:29, Shridhar Daithankar wrote:
> > I remember reading in one of the HP guides regarding 64 bit that 64 bit is a
> > tool provided for applications. In general no app. should be 64 bit unless
> > required. In fact they advice that fastest performance one can get is by
> > running 32 bit app. on 64 bit machine because registers are wide and can be
> > filled in is less number of fetches.
> >
> > Sounds reasonable to me.
>
> Dou you, the programmer or SysAdmin, always know when 64 bits is
> needed?
>
> Take, for simple example, a memcpy() of 1024 bytes. Most CPUs don't
> have direct core-core copy instruction. (The RISC philosophy, after
> all, is load-and-store.) A 32-bit executable would need 1024/32 = 32
> pairs of load-store operations, while a 64-bit executable would only
> need 16. Yes, L1 & L2 caching would help some, but not if you are
> moving huge amounts of data...
Well, that wasn't intended application aera of that remark. I was more on the
line of, I have 16GB data of double precision which I need to shuffle thr. once
in a while, should I use 32 bit or 64 bit?
Something like that.. bit more macroscopic.
I work on an application which is 32 bit on HP-UX 64 bit. It handles more than
15GB of data at some sites pretty gracefully..No need to move to 64 bit as
yet..
Bye
Shridhar
--
Kramer's Law: You can never tell which way the train went by looking at the
tracks.