[geeks] Itanium 32 bit performace.... hahahaha

[Jochen Kunz]

On Wed, Dec 10, 2003 at 08:25:57AM -0500, Kevin wrote:

> I've heard this before, but have never understood it.  What is it
> about Alphas that requires more RAM than other processors?  
Instruction set architecture and memory alignment constrains.
The memory alignment constrains are mostly there to ease the design
and implementation of the memory controller. That way the memory
controller can be optimized for maximum throughput. Most (early) 
high end Alpha designs use a 256 bit memory bus to get a high memory 
bandwith where low end designs use only 64 bit. A high memory bandwith 
is essential for a 64 bit RISC CPU due to its higher memory utilisation.

E.g. a NetBSD/VAX (to name the other extreme) GENERIC kernel binary 
needs only a bit more then 1.5 MB but an Alpha GENERIC kernel close 
to 7 MB. 128 MB RAM is a metric butload of RAM for a VAX but only a 
breakfast for an Alpha. 

> My Alpha has 256 and seems to run fine as a file server.
Depending on the OS (*BSD?) and workload 256 MB is a reasonible amount
of RAM for an Alpha. I got a slightly loaded Alpha with NetBSD and 
Mozilla or gcc fast to using all RAM, 128 MB in that case. I ended 
trading this PC164 based 500 MHz Alpha sans RAM for a HP9000 C240. 
The PC164 needs 8 pieces of rather expensive 32 MB or 64 MB FPM 
PS/2 parity RAMs to get "usable". I got 512 MB RAM for the C240 for 
20 EUR and the raw CPU computing speed is comparable. And most 
important: The C240 is my first, one and only PA8k i.e. 64 bit 
PA-RISC machine where that Alpha was only one of, ehhm, 7 Alphas 
in my machine room.
-- 



tsch|_,
         Jochen

Homepage: http://www.unixag-kl.fh-kl.de/~jkunz/