Re: 32-bit vs. 64-bit x86 Speed

haberg@math.su.se (Hans Aberg) writes:
>>From what I have heard, a 32-bit program compiled for a 64-bit CPU, will
>in effect run in something alike 32-bit emulation mode. (A deliberate move
>in the design of the 64-bit architecture, in order to avoid portability
>problems.) So unless it actually has new code, directly rewritten as to
>take advantage of the 64-bit architecture, it will in fact run somewhat
>slower (of the CPU frequencies are the same).


Slower than what? E.g., looking at our Latex benchmark again, I see
that the Athlon 64 beats a faster clocked Athlon XP even in 32-bit
mode:


    Machine time (s)
- Athlon XP2700+, 2170MHz, 256KB L2, Debian 3.0 1.0
- Athlon XP2800+, 2083MHz, 512KB L2, Fedora Core 2 0.92
- Athlon 64 3200+, 2000MHz, 1MB L2, Knoppix 3.3 (32-bit) 0.87


Likewise, a 2400MHz Core 2 beats a 2000MHz Pentium M by more than a
factor of 1.2:


- Pentium M 2000MHz (IBM Thinkpad T42p), 2MB L2, Debian Etch 0.837
- Core 2 Duo E6600, 2400MHz, 4MB L2, Debian Etch (32-bit) 0.652


    - anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/

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