The "SPEED" of progress

[Harrison]

Something else quite interesting I just discovered. An AMD Athlon 500MHz CPU actually had a theoretical peak of 1GFLOP as it's instruction set allowed two operations per cycle, making it twice as fast as a Pentium 3 500MHz CPU! I bet you didn't know that at the time!

[AlexJ]

I always knew there was a reason I bought AMD instead of Intel! Still did anything actually take advantage of it, or was the speed difference noticable in tests?

[Harrison]

Yes, it was noticeable as this was a feature built into the main instruction set of the Athlon range so was taken advantage of during all CPU operations. Obviously all the other system architecture did effect the overall speed, so the fact that both Pentium 3's and Athlon's were using slow 100MHz and 133MHz DIMMS at the time wouldn't have helped.

But interestingly before the Athlon, AMD CPUs were actually slower than 1 floating point operation per clock cycle, compared to Intel which were always 1 measures as 1 per cycle, so before the Athlon range the AMD CPU's were slower than Intel CPU's on a clock for clock basis.

The introduction of the first Athlon with double the operations per clock cycle was the turning point for AMD and the point when AMD CPU's started to gain popularity. My first AMD CPU was a 400MHz K3 CPU in a laptop, so that would actually of had a MFLOP rating under 400MFLOPS, whereas my next was an Athlon 900MHz PC I had at work which would of had 1800MFLOPS.

[AlexJ]

The introduction of the first Athlon with double the operations per clock cycle was the turning point for AMD and the point when AMD CPU's started to gain popularity. My first AMD CPU was a 400MHz K3 CPU in a laptop, so that would actually of had a MFLOP rating under 400MFLOPS, whereas my next was an Athlon 900MHz PC I had at work which would of had 1800MFLOPS.

My first AMD chip was a K6-166MHz which had 197MFLOPS.

[Harrison]

Are you sure that is MFLOPS and not MIPS?

MIPS = Millions of instructions per second.

Those are different and are derived from benchmark results and cannot be compared between CPU families.

[Stephen Coates]

The P3's 32bit PCI bus runs at 33MHz and can push a maximum of about 125MB/s to say a PCI graphics card. In contrast a current PCI-E interface of today can push a maximum of 8GB/s. A huge increase you have to agree. Next the IDE interface. The old PATA interface the P3 is using would probably be the original ATA33 version with a maximum parallel bandwidth of 33MB/s, equally around 10MB/s actual data transfer. In contrast today an SATA interface has a maximum serial bandwidth of 300MB/s, with the current SATA2 drives easily managing 100MB/s sustained transfer.

And my AGP graphics card...?

[Harrison]

Your AGP graphics card slot speed will depend on the speed of the actual AGP slot in your system and the supporting AGP speed of the graphics card installed in it.

All AGP slots run on a 66MHz system bus which is twice the speed of the PCI slots. The original AGP 1x slot specification allowed a maximum data rate of 266MB/s, and as the AGP slot developed, faster 2x, then 4x and finally 8x AGP slots appeared. But the graphics card needed to still support the maximum speed of the slot, or it would clock down to the speed of the card, so a 4x AGP card in a 8x slot would still run at 4x speed.

All AGP slots still ran on a 66MHz bus speed, but for the faster AGP slot types the channel is double pumped for 2x, quad pumped for 4x and strobed eight times per clock for 8x AGP speeds, meaning that in theory the actual theoretical speed is actually 2x, 4x or 8x faster than the original 66MHz bus speed. This makes the 8x AGP speed a maximum of 2GB/s, which is roughly 4 times slower than PCI-E. Although also take into account that most motherboards, their north bridges, and the system ram at the time could not shift data this fast until quite late in the AGP slot's life.

For the age of your P3 I would guess it is using an AGP 2x slot and the graphics card is also a 2x speed specification. This means your graphics card is running on a double pumped 66MHz bus, effectively making it 133MHz, with a maximum datarate of 533MB/s.

Comparing this obsolete AGP 2x slot with the current PCI-E graphics slot, your P3's AGP slot is roughly 16 times slower at data transfer compared to the current standard.

BTW, did you know that early 1x and 2x AGP graphics cards are not compatible with later 4x and 8x slots? Putting such early cards in the later slots could completely fry the motherboards beyond repair due to a different core voltage being used in the two different specs.