Barefeats have just updated their "G4 vs Athlon vs Pentium 4" page. Not only is the Xserve beaten by a 1.6Ghz Athlon in every test but it's beaten by the dual Ghz G4 tower in some of them aswell, only managing to match it rather show any improvements you might expect from it's DDR RAM. I know it's still just a 133Mhz FSB and the DDR is there to provide bandwidth for the drives and networking, not for the CPU but you'd think there'd at least be a tiny improvement over the tower.
Let's just hope we get a real DDR version of the G4 not some hack of a chipset like the xServe uses on the new towers when they're out. Most benchmarks seem to show an 8 - 10% improvement over PC133 when DDR266 is used, with the G4 having a lower clock speed than an athlon or Pentium 4 but a fairly high IPC rating, DDR would really benefit a G4.
The 1GHz G4 in the test has a 133Mhz FSB, 256K L2, 2Mb L3 and SDRAM, it's between 20% slower and 26% faster than a 2Ghz Pentium 4. Assuming the Pentium 4 is the 2000A northwood model it's got a 100Mhz FSB x 4, 512K L2, no L3 and 800Mhz RDRAM yet it's only managing to push out the effective performance of a 1.266Mhz G4 assuming the G4 was the same kind and on the same motherboard as the 1Ghz G4.
Here's the pentium 4 I assume is used in the test :
2Ghz (Northwood 2000A)
512K L2 @ 2Ghz : SRAM - (100% of clock speed)
100Mhz x 4 FSB : RDRAM (40% of clock speed)
The dual Ghz G4 used in the test :
1Ghz - (PPC7455 / Apollo)
512K L2 @ 1Ghz : SRAM - (100% of clock speed)
2Mb L3 @ 250Mhz x 2 : DDR - (50% of clock speed, 4:1 ratio x 2)
133Mhz FSB : SDRAM (13.3% of clock speed)
here's how I see DDR would benefit a G4 using the rumoured specs of the new G4 :
1.4Ghz - (actually 1.4166 Ghz because of the FSB speed)
512K L2 @ 1.4Ghz : SRAM - (100% of clock speed)
2Mb L3 @ 354Mhz x 2 : DDR - (50% of clock speed, 4:1 ratio x 2)
166Mhz x 2 FSB : DDR (23.5 % of clock speed)
It would still be below the Pentium 4 as far as how much slower the main system RAM runs when compared with CPU but baring in mind how much damage a 1Ghz G4 with SDRAM does to the 2Ghz Northwood, I can only imagine what sort of results we'd see pitting a G4 with the above specs against a Northwood. Given the fact the G4 has to work a lot less than a Pentium 4 to get the same or better results we're in for a real treat when we finally get DDR on the mac.
It's just the whole idea of it being as useless as the Xserve as far as performance is concerned, you can't really feed a 1Ghz chip enough with 133Mhz SDRAM as it is, if it still only pushed 133Mhz of bandwidth from the RAM to the CPU on a 1.4Ghz G4 it really would be a waste of potential power.
