AMD 266 Mhz FSB?

[matrix]

how come they advertise the new
t-birds as having 266 mhz fsb?

can anyone give me more info?
because i do not own an amd chip.

does it really have a 266 bus?
or is it marketed that way for DDR?
what does this mean?
does the clock multiplyer go down
cuz of a faster bus?
does ram go twice as fast?

please.. give me the low down.

[UnseenMenace]

The 266 mhz is the internal speed of the CPU and refers to a double pumped FSB ( 2 x 133 mhz ) in the same way the 200 mhz CPU's refer to a CPU which runs as a double pumped 100 mhz FSB ( 100 x 2 )

[DjPhilip]

If you buy the chip, just check the letter "c" at the end of the 2nd line. A "b" indicates a 100fsb processor.

[matrix]

i still dont follow
y would they advertise it as 266mhz ..

i mean.. how is it better than a regular
t-bird 133 mhz..

[dozier768]

because the fsb is 133 x 2 that equals 266. well effectivly anyway the data is sent on the high and low side of the clock cycle rather than just the tradidional high efectivly giving you twice the bandwidth

[Phil]

matrix (Jun 17, 2001 11:45 a.m.):
i still dont follow
y would they advertise it as 266mhz ..

i mean.. how is it better than a regular
t-bird 133 mhz..

There is no tbird 133mhz
the athlons have always used a ddr Front Side Bus. The first ones ran on a 100mhz fsb which was ddr so became 200mhz, more recentally then ran at 133mhz which because of the bus being ddr is 266mhz. It is only recentally that they have started using ddr memory as well.

[matrix]

so..
the 266 mhz t-bird is designed for DDR ..

so can i say the P III or P4 .. with DDR..
has a 266 mhz fsb too..
becuase it transfers bandwith at both
ends of the cycle.

[indigo]

No, let's clarify.

There are two different busses here which are getting confused.

The first is the CPU to Chipset (Northbridge) bus. This has always been 100MHz DDR, and more recently 133MHz DDR.

The second is the Chipset (Northbridge) to System Memory bus. This has been 100MHz PC100, 133MHz PC133, Virtual Channel 100 or 133, and most recently PC1600 (100MHz DDR) and PC2100 (133MHz DDR).

I'll give you a few examples:

Via KT133 based motherboards had a 200MHz Front Side Bus (100MHz DDR between the Northbridge and the CPU), but they could only handle PC100 or PC133 RAM.

The Via KT133A helped the situation by synchronizing the address cycles (while 100MHz DDR can send data at 200MHz, the address cycles still run at 100MHz). Now if you had PC133 RAM, you didn't waste 25% of your address cycles because the KT133A could run the FSB at 266MHz (133MHz DDR).

More recently you see KT266 and AMD760 based motherboards that not only synchronize address cycles, but due to the use of DDR RAM they also have more bandwidth.

So AMD calling their processors 266MHz is legitimate as they are referring to what the FSB is, not what type of RAM is used since they have no control over that. It would be better to call the chips 133MHz DDR parts since 133MHz DDR and 266MHz SDR are not the same thing (the SDR performs better), but it is technically correct in a way. Stricly speaking Hertz is cycles per second. In 133MHz DDR there are 266MHz worth of data cycles. This is technically correct. However nobody tells you that part of the RAM (the address cycles) is limited to 133MHz. A 266MHz Single Data Rate part would have both running at 266MHz.

Anyways, more than you asked for, but the Pentium 4 has Dual 64bit Channels running at 100MHz DDR, so they claim 400MHz FSB.