[conspire] Re: Last Year's Supercomputer

[Mark S Bilk]

In-Reply-To: <20030619030945.GB15323 at myrddin.imat.com>; from mhigashi at imat.com on Wed, Jun 18, 2003 at 08:09:45PM -0700
Organization: http://www.cosmicpenguin.com/911

On Wed, Jun 18, 2003 at 08:09:45PM -0700, Mike Higashi wrote:
>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.

No -- the original bargain motherboard that I had intended to get, 
ECS K7S5A-Pro, supports only 266MHz (FSB/DDR) CPU and memory.
Then someone told me about the FIC AU13 Pro motherboard, using the
superior nVidia nForce2 chipset, which, among other things, will
run pairs of memory sticks in parallel, effectively doubling the
transfer rate (probably the same as described below for Pentium 4).

However, I decided to go with the somewhat more expensive Asus 
A7N8X Deluxe, which uses the same chipset, because it's rated for 
400MHz (FSB/DDR) CPU and memory, even though the processor I chose 
has only a 333MHz FSB bus, since I figured the FIC board might be 
running closer to its margins than the Asus, and I've been pleased
in the past with Asus design and workmanship.  I didn't believe FIC
when they told me they had never tried a 400MHz CPU in the board;
I think they did (why wouldn't they?) and it didn't work.

Finally, the reason why I bought 333MHz (DDR) memory to use with 
the 333MHz (FSB) CPU is that the Asus tech support guy I talked 
with (a gamer who uses the A7N8X himself) told me that the system 
actually slows down if the memory is run at a higher speed than 
the CPU.  (I think their support database also says this.) So I 
saved a few bucks by getting the slower memory.

>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.

So then is my system only 16% ((400 - 333)/400) slower in actual 
CPU bus and memory rate, than an "800MHz" P4?

  Mark