[geeks] w00t! AlphaServer SMP goodness

[Jochen Kunz]

On Sat, Nov 02, 2002 at 04:31:43PM -0600, Eric Dittman wrote:

> One thing to remember is the PWS and the PC164 use different
> chipsets.  The memory access speed is also different, and
> the PC164 can bet set for 128- or 256-bit memory width, so
> if it is set to 128-bit that will slow down memory access
> also.
The PC164 runs in 128 mode. Unfortunately I have not enough SIMMs
to run it in 256 bit mode. The memory access speed ist not that 
different. The SDRAM runs with "83 MHz" = 12 ns. This is the speed
of data transfers. But you have a latency of several cycles when 
a new address is accessed. That is more or less in the magnitude
of FPM / EDO RAM. Accesses of subsequent addresses are faster 
than the first access with SDRAM and FPM RAM. The only difference
is the interface, the "bit bucktes" that do the actual data storage
are the same, regardless what type of DRAM. 
What SDRAM makes "faster" is the ability to pipeline. You can do 
things like: "Command: read addr. A", "Command: read addr. B", 
"Transfer: data A", "Transfer: data B".
(At least a hardware designer explaind it that way to me.)

But the different memory bandwith of the two systems can't make 
a difference that is that big. I think it is really GCC, what 
makes the difference. (Look at SGI/IRIX with MIPS Pro compiler
and GCC. GCC code is knowen to be slower on that platform too.)
-- 



tsch|_,
          Jochen

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