[CentOS] Re: maximum cpus/cores in CentOS 4.1 -- [OT] How EV6 differed from GTL

Bryan J. Smith b.j.smith at ieee.org
Thu Sep 8 19:11:02 UTC 2005

"Bryan J. Smith" <b.j.smith at ieee.org> wrote:
> Digital EV6 platforms have ports (up to 16) into a
> "crossbar switch."  The logical front-side bus is also 
> 64-bit, including S462.  Again, any claims of "dual DDR" is
> actually an interleaving hack, done in an attempt to reduce
> latency and increase overall throughput.  But it is not the
> same as S939/940's _true_ 368 traces for a _true_ 128-bit
> DDR.

I should point out that it _is_ possible to have two (2) or
even more DDR channels connected to an EV6 crossbar.  And you
could have _multiple_ CPU, which are on different "ports,"
bursting traffic to different memory channels on different
memory "ports."

But _none_ of the "dual DDR" Athlon implementations did that
AFAIK.  Only Digital Alpha 264 systems used multiple 64-bit
memory ports.  It was commonly 2, 4 or 8 EV6 Alpha 264 CPUs,
with 2 or 4 SDR/DDR memory channels and a few 64-bit PCI
bridges, to round out the maximum of 16 "ports" into the

The Athlon MP (AMD762 northbridge) platform used only 5 ports
-- 2 CPU (each CPU had its own interconnect), 1 memory, 1
PCI32 at 266MHz (AGP2.0 aka x4) and 1 PCI64 at 33 (AMD766) or 1
PCI64 at 66 (AMD768).  Supposedly up to four (4) AMD762
northbridges could be used in a system -- connected to each
other using the PCI32 at 266MHz channel (normally used by AGP). 
But no PC mainboard I saw ever did (and by the time API came
around, they were only using one AMD762 for Alpha 264

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