where's the multiplier?

wrote:
I assume that the memory multiplier is internal to ram , and so the
mobo tels the ram what multiplier to use. Thus far, - it seems to
me - memory is unlocked.

Err, memory multiplier? I think you may be slightly confused here ...

SDRAM - Is Synchronous with a capital S, so it has a clock. And all
clocked devices in a computer derive their clock from the FSB. And if
they're not running at the speed of the FSB, then they must be using a
multiplier (or dividor). I recall running FSB=100, and SDRAM at
133MHz. then some electronics (a memory multiplier and/or dividor )
was making it run at 4/3 (as in four thirds) times the FSB. The
question, was then whether this thing (which I was calling a ''memory
multiplier'), is inside the memory - just as the CPU multiplier is
inside the CPU. I assumed it was inside, and that the only significant
difference, was that memory clocks are not locked, - they listen to
the speed suggested by the mobo.

Well, it possibly gets a little curly RAM is clocked "externally" in the
sense that they operate exactly at the speed they are fed with by the
northbridge. This is why the ability to run ram async to the FSB is chipset
dependent, not RAM dependent. The situation in non-K8 system is:

Other stuff (southbridge, AGP, etc)
^ ^ ^
| | |
| | |
| | |
CPU --- FSB --- Northbridge ---- System clock
^
|
| RAM bus
|
V
RAM

The CPU is fed the system clock for the FSB, but the northbridge doesn't
always feed this same clock to the RAM. It can apply a 4/3 multiplier or
other variations to it beforehand. However, you could say that some RAM does
have an internal multiplier. DDR sort of has a 2x multiplier, and QDR sort
of has a 4x multiplier. These are fundamental to the RAM chips themselves
(ie: what make DDR DDR) so obviously cannot be changed.

The K8 situation is slightly different, though still has the same
fundamental idea. Rather than repeating myself, I'll refer you to
http://www.emboss.co.nz/amdmults/k8mults.html
(readme file from my A64 clock viewer tool)

--
Michael Brown
www.emboss.co.nz : OOS/RSI software and more
Add michael@ to emboss.co.nz ---+--- My inbox is always open

wrote:
thanks for that info. I pity the BIOS programmer that includes a drop
down menu where the user 'selects a speed' !
Most speeds probably aren't supported (unless processors have 30
multipliers going from 0 to 15 in 0.5 increments!),. The drop down
menu is misleading - and a misleading GUI is dangerous. And that's
just from the user's perspective.
I imagine that the only reason they don't cause people problems is
that CPUs nowadays are multiplier locked!

Works perfectly for my AMD XP1800+ T'bred B CPU on an nForce2 Ultra 400
chipset mobo. I just select 10.5 x, put the FSB at 200MHz and up the vcore
to 1.775 and she flies. 2.1GHz instead of the 1.53 it was sold as, still
using the AMD-supplied heatsink and fan.

CBId gives it a XP2750+ rating but in reality it's faster than that due to
the 200MHz FSB. It crunches SETI WUs in ~107% of the time an XP3200+ takes.
(On the same mobo).

Confused yet?
--
~misfit~