Re: Dual Core vs. Dual CPU

[Bill Davidsen <davidsen@tmr.com>]

Urs Thuermann wrote:

>I'd like to know what is the difference between a system with a dual
>core CPU compared to two (single core) CPUs.  I know dual core means
>two CPUs on one chip, but is it really two complete CPUs or do they
>share some component which is used by both CPU cores?
>
>For example HT duplicates only those parts of CPU which hold the state
>of the program in execution (i.e. program counter, registers, etc.)
>but they share the execution logic which often leads to performance
>loss. 
>
>Is there some performance difference between dual core and two real
>CPUs, too?  I assume the dual cores on one chip must share the bus
>interface, but since in a multi CPU system only one CPU can access the
>bus at a time, I think this doesn't make a performance difference,
>right?
>
>Can anybody give some clarifiactions on these issue?
>
The bad part is that the cores share a bus connection, the good part is 
that it appears that some IPC can be done on chip.

RELATED: has anyone done a measurements on the 955 chip, which is dual 
core and HT? On heavily threaded or parallel tasks I find 20-30% drop in 
clock time for HT processors, but I wonder if the CPU runs out of memory 
bandwidth. My standard test is a kernel compile.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979