[conspire] Re: Last Year's Supercomputer

[Mike Higashi]

On Mon, Jun 16, 2003 at 11:29:35AM -0700, Rick Moen wrote:

> Quoting Mark S Bilk (markbilk at attbi.com):
> 
> > Asus tech support says that running RAM faster than the CPU actually
> > slows down performance....
> 
> <snort>
> 
> There's roughly zero risk of that when your CPU is running at 2 GHz.
> Remember, that's the whole reason we have L1 and L2 caches.

Actually, what he's talking about here is the speeds of the memory and
bus that connects the cpu with the memory, aka "Front Side Bus" or FSB.
Although 400MHz DDR memory is out now, Mark got 333MHz since his
motherboard doesn't support speeds higher than that.

The lingo used in memory is also kind of tricky. A 333MHz FSB really has 
a clock speed of 166MHz, but since DDR (or "double data rate") memory
uses both the rising edge and the trailing edge of the clock signal to
trigger memory transfers, it has an effective transfer rate of 333MHz.

Where it gets really tricky, and perhaps even deceptive, is the memory
speeds used with Pentium 4s. Using the same speed of memory they get
another doubling of the transfer rate (I'm not sure why, but it may be
because it simply uses pairs of DIMMS to increase the bandwidth.) So the
P4s and their motherboards make speed claims of 533 or 800MHz, when it's
really a 133 or 200MHz clock being multiplied by four.

Mike