On Tue, 13 Apr 2004 00:35:58 +0200, somebody wrote:
On Sat, 10 Apr 2004 13:01:39 -0700, "Jim" wrote:
Ok, one problem here is that the marketing hype leads the advertising people
to not quite state things correctly. Let's forget the details of that ad,
and talk as accurately as possible.
The CPU FSB is more correctly stated as 200MHz (actual), but since it
employs DDR technology, it's *effective* rate is 400MHz. The "400MHz"
number you see in the ad is actually misleading, the CPU FSB does NOT
physically *run* at 400MHz, it runs at 200MHz (that's what would show up on
a scope!), *but*, because the DDR technology it employs allows data to
travel BOTH on the up and down side of each cycle (per MHz), it's *behaving*
as if it data was traveling on ONE side of the cycle, but at 400MHz! Get
it? It's a marketing gimic, the CPU isn't actually *faster*, it's more
*efficient* (2x in fact) at the same speed of a 200MHz processor (1x) that
does NOT employ DDR technology.
The clock is just that. It's just a clock. It might run at 'just' 200
MHz, but it's _NOT_ the speed of the bus! The speed of the bus is
400MHz, and there's no marketing gimmick about that. That is indeed
the _speed_!
Bus speed is measured by the clock cycles. The speed is 200MHz, not double
that or 4 times that. That is the data rate. Data rates are measured in
Bps or bps, not MHz. And anyone that thinks any different is just a stupid
stubborn idiot. Granted, that the bandwidth no longer depends on bus
speed, but data rate. The cpu clock speed does however depend on the bus
speed. Every cpu has a multiplier that sets the cpu clock speed in
accordance with the FSB speed. And now just a few problems that can arise
from calling the data rate the the FSB speed.
Tell an engineer to build you a MB with a 400MHz bus do you think they'll
know that you really only mean 100, or 200 in AMD's case.
Use that 400MHz to calculate your cpu speed and see how far off you'll be.
Now what purpose does the clock have? It's like this: When data is
transmitted on the FSB, data is represented on the 72 pins (64 + ecc)
out by voltage levels. But as the data have to change to a new value,
how do we know _when_ to read the data? When are all the leads ready,
and the data correct? That's where the clock comes in. The clock syncs
the transfer. And that is the _ONLY_ purpose of any clock. The clock
tells _when_ the data is supposed to be ready, and ok to read. Now, you
can sync on the clocks rising flank, or you can sync on the falling
flank. ... - Or, _both_!
A good example of DDR. If the clock speed doesn't mean anything, why does
the term DDR exist?:-)
AMD's FSB is the DEC Alpha EV6 protocol bus. And this happens to sync on
both rising and falling flanks.
So for a bus speed of 400MHz, - a 200MHz clock is _required_! The data
on the pins change 400 million times per second. That's the _SPEED_ of
bus! And that's only thing that matters, and marketing is entirely 100%
correct in stating that FSB speed is 400MHz. That is not marketing hype
or a gimmick.
But you are forgeting the major point. Bus speeds are mearsured by clock
speeds. Data speeds are measured by throughput in bps/Bps. Saying the bus
speed is 400MHz simply because the data rate is DDR is like saying my car
is going 120MPH when I have 2 people in it actually doing 60MPH.
I suppose I have to blame Intel marketing for everybody to be so damn
hung up on clockrates. - Hey, guys, - it's just a clock!
And without a clock, absolutely nothing in the system would work. I blame
both Intel and AMD for trying to change standard engineering practices by
multiplying apples (clock in MHz) times oranges (data in bps) and then
calling the final number apples. Pure BS.
As for DDR ram, I don't know how it works, but I assume the actual
transfer is something similar to the EV6 bus. But there are more complex
things involved with memory access. DDR speed only affects the bandwidth
that memoryblocks can be transferred with. An actual access is slower. A
long chain of things need to respond,
DDR ram is designated by bandwidth. PC2100 ram has a clock rate of 133MHz.
PC3200 has a clock rate of 200MHz, not 400 as you'll see all over the
f*cking place now.
And as my last comment on this. When I pinned AMD to the wall, they
admitted that their bogus FSB speeds were just that, by saying that it's
the effective clock rate when compared to a non DDR bus.
--
Abit KT7-Raid (KT133) Tbred B core CPU @2400MHz (24x100FSB)
http://mysite.verizon.net/res0exft/cpu.htm