Archived from groups: alt.comp.hardware.pc-homebuilt (
More info?)
To restate, PC2100 will work as long as the mobo indicates so in the spec
(133MHz clock, or 266MHz DDR) *and* there's a 3:2 CPU/DRAM ratio supported
by the chipset to insure both the CPU and memory can actually run at spec,
at the same time (as I recall, this is the case).
IOW, what the mobo specs show is ALL the options on CPU and memory, but what
they don't explicit say is which *combinations* are supported, that requires
an examination of the manual. You can't, for example, run a P4 800MHz CPU
(w/ 200MHz clock) and PC2700 (166MHz clock) AT THE SAME TIME (not at clock
anyway) because that would require a 6:5 CPU/DRAM ratio (200 / 6 * 5 = 166),
which is not supported in the Canterwood chipset. The closest available
CPU/DRAM ratio is 5:4 (200 / 5 * 4 = 160). If you installed an 800MHz CPU
*and* PC2700 together, for example, the Asus mobo would have no choice but
to underclock the memory slightly (160MHz) using 5:4 to make it run at all.
IOW, that PC2700 would actually be running 320MHz DDR (2 x 160Mhz clock),
which is PC2560 (320 * 8 bit wide).
To illustrate, examine pg. 2-11 of the P4C800-E Deluxe manual, notice the
asterisk next to the PC2700 entry on the 800MHz CPU line, in the matrix (
ftp://ftp.asus.com/pub/ASUS/mb/sock478/P4C800E-DX/e1347b_p4c800-e_deluxe.pdf
). That's why that's there!
But back to your PC2100, the only *caveat * is, it will run asynchonously to
the 800MHz CPU in terms of clock, thereby not ideal. Of course, I'm
assuming you would never undeclock the CPU from 200MHz down to 133MHz FSB
*just* to gain synchronization w/ the PC2100! If that's what you're
thinking, no. That would be letting the cart drive the horse, and only make
matters worse.
Jim
"Fabio Santoro" <cage66@coqui.net> wrote in message
news:ANyfc.7093$pk5.7083@fe03.usenetserver.com...
> Thank you for responding.
>
> So Jim this will be the same senario as in the past with PIV on 400Mhz.
FBS
> and using PC-133 SDARAM.
>
> I bought a ASUS P4C800 Motherboard with INTEL 875P Chipset ( called
> Canterwood, i think).
>
> The manual says on 800 Mhz FBS configuration 266/333/400 Mhz DDR can be
> used.
>
> "Jim" <null@null.com> wrote in message
> news:WUxfc.4713$Yf6.3627@fed1read07...
> > If you mean use the PC2100 from the other system in the new P4 mobo,
well,
> > assuming the mew mobo supports memory options of 266/333/400 DDR, you'll
> be
> > running your memory at the lowest option! And asynchronously to the CPU
> > FSB. That pretty much tells the story, and it's not a good one.
> >
> > Your P4 800MHz is actually FSB 200MHz (clock). The PC2100 memory is
> 133MHz
> > clock. To use these in combination requires a CPU/DRAM ratio of 3:2
> > (probably supported by the chipset, assuming this is the 865/875 Intel),
> > calculated as (200 / 3 * 2 = 133).
> >
> > In general, it's best to run the CPU FSB and memory clocks "in sync",
you
> > just get better performance. Ideally that P4 800MHz would be much
better
> > served w/ PC3200 (200MHz clock). And if you intend to overclock the
CPU,
> > matters get only worse. Every increase in CPU FSB also increase the
> memory
> > clock, and since the PC2100 taps out so early, there's little if any
> > headroom in that memory for overclocking (not without increasing the
> > CPU/DRAM ratio even further). For people who intend to OC the CPU FSB,
> they
> > often look for *more* than PC3200 (e.g., PC3500, PC3700), just to
prevent
> > this sort of problem. But for non OC'ers, PC3200 is the best match.
> >
> > Anyway, as long as the chipset supports a 3:2 CPU/DRAM ratio with those
> > component, it all still works. But memory will be a drag, no doubt
about
> > it. Most system suffer from memory bandwidth limitations anyway, even
> using
> > PC3200. By using PC2100, you're already losing 1.1Gb/sec
(theoretically).
> > How this affects real world applications just depends on how you intend
to
> > use the system. Obviously, memory intensive applications will suffer
> most.
> >
> > And we didn't even talk about dual channel yet. While rather overblown
as
> > to its affects on performance, even the worst cases show a 5-10%
> > improvement. But unless you have at least a "pair" of matched memory
> > modules, you can take advantage of it. So if that PC2100 512MB is only
a
> > single stick, you're even worse off -- you can't even exploit the dual
> > channel features of your new mobo! (assuming it is dual channel
capable).
> >
> > HTH
> >
> > Jim
> >
> >
> > "Fabio Santoro" <cage66@coqui.net> wrote in message
> > news:Kpxfc.7073$pk5.3647@fe03.usenetserver.com...
> > > I bought a ASUS motherboard for Pentium 4....and I'm planning to put a
> > 2.GHz
> > > HT 800 MHz FBS. Prescott CPU but I currently have a AMD system with a
> > > ATLHON XP 2200+ CPU with a 512MB PC-2100 memory module....if I use
that
> > > memory module in that configuration how will be the performance?
> > >
> > >
> > >
> >
> >
>
>
>
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