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Originally posted by hitechjb1
This 939 platform memory bandwidth, as estimated from some test data (so result is preliminary), is impressive. Its efficiency is around 86-90%, which is 15-20% (to be confirmed with more 939 test data) better than the P4 QDR dual channel counterpart.
Its effective bandwidth (not max), running at the same memory bus speed, is about 15-20% higher than that of P4 QDR dual channel and 81-89% higher than that of 754 platform or nforce2 dual channel.
Estimation and importance of 939 platform memory bandwidth
A major difference between the AMD 754 and 939 platforms is the memory bus, i.e. 64-bit memory bus for 754 vs the 128-bit memory bus for 939. Here put it some estimate (since 939 is not commonly available yet) to see the potential impact on memory bandwidth performance.
I think there is a significant advantage from the 939 128-bit memory bus and on-chip dual channel controller, it is very different from the nforce2 dual channel which has only few % memory bandwidth improvement over single channel, as shown below.
memory_bandwidth_efficiency = effective_memory_bandwidth / max_memory_bandwidth
1. In the P4 arena, the dual channel QDR efficiency is around 75% with 64-bit memory bus
max_memory_bandwidth = FSB x 4 x 8 = 32 FSB
effective_memory_bandwidth = FSB x 4 x 8 MB/s x 0.75 ~ 24 FSB
2. XP nforce2 single channel efficiency ~ 85-90%
max_memory_bandwidth = FSB x 2 x 8 = 16 FSB
effective bandwidth = 0.875 x 2 x 8 x FSB ~ 14 FSB
3. XP nforce2 dual channel effieiency ~ 90 - 95% (actually should be 45-48%, depends on how it is counted)
max_memory_bandwidth = FSB x 2 x 8 x 2 = 32 FSB
max_FSB_bandwidth = FSB x 2 x 8 = 16 FSB (FSB limits dual channel memory bandwidth)
effective bandwidth = 0.925 x 2 x 8 x FSB ~ 14.8 FSB
4. 754 hardwares have been around for a while, and we have seen its memory bandwidth being around 95%.
For 754 platform, memory bandwidth efficiency ~ 95%
max_memory_bandwidth_754 = 2 x 8 x memory_bus_frequency = 16 memory_bus_frequency
effective bandwidth = 0.95 x 2 x 8 x memory_bus_frequency = 15.2 memory_bus_frequency
E.g. from Maxvla's system screenshot (http://www.maxvla.com/host/komusa4200b.jpg), a 754 memory benchmark (integer buffered iSSE2) shows the 754 memory efficiency being around 4574/4800 = 95%.
At 300 MHz, the max bandwidth would be 4800 MB/s for single channel, and 9600 MB/s for 128-bit bus (theoretical max).
5. For the 939 128-bit memory bus, there is a good possibility that it could be higher than 75% (the P4 QDR number) due to its direct 128-bit memory bus:
- max_memory_bandwidth_939 = 2 x 16 x memory_bus_frequency = 32 memory_bus_frequency
- At 80%, 300 MHz, the effective bandwidth would be 7680 MB/s
- At 90%, 300 MHz, the effective bandwdith would be 8640 MB/s
- At 95%, 300 MHz, the effective bandwdith would be 9120 MB/s
(ECC is not required in 939).
I think the 128-bit memory bus could be more efficient than the 64-bit QDR, hope it is close to the single channel number ~ 85-90%. This will be confirmed when actual 939 hardwares come out. (Will see)
...
Summary (preliminary numbers, may vary as more 939 test results become available):
- If further confirmed by more 939 hardwares, this 86 - 90% number on bandwidth efficiency for 939 128-bit is 15 - 20% higher than the 75% QDR of P4 (64-bit).
- At 86-90% efficiency, the effective bandwidth for the 939 128-bit memory bus would be 81 - 89% higher than that of a 754 64-bit memory bus, with assumed 95% memory efficiency.
This higher bandwidth in 939 would have significant impact on memory intensive applications such as video and image streaming, applications using spatially structured data as in scientific computation, ..., as well as 3Dmark01.
We'll see this with the 2.4GHz 3700+.From a few gaming benchmarks, a A64 FX/939 at 2.4 GHz performs 12-20% better than an A64 754 with 1MB L2 at 2.0 GHz, and 15-29% better than an A64 754 with 512 L2 at 2.0 GHz (memory bus, HT bus same frequencies). Not clear if 754 CPU's were clocked to same speed, what would the performance difference be, as the performance difference can be attributed to both memory bandwidth and CPU raw power, but these numbers put an upper bound on gaming performance of 939 over 754. From looking at another set of game benchmarks with both a 939 (512 KB L2) and a 754 (1 MB L2), both running at same frequencies, they are about tie.
However, the question of the practicality is raised for the everyday consumer in regards to the $700+ 1mb L2 DC-enabled FX-53... Initially, the consumer may have the choice, realistically, between the 1mb SC Clawhammer, and 512k DC Newcastle. The Clawhammer option will probably disappear in a couple of weeks.hitechjb1 said:Please note that in that article comparison, the two 939 have only 512 KB L2 whereas the two 754 have 1 MB L2.
It is known that twice the size of L2 have few % performance advantage on the average for many programs.
That is also why ClawHammer (1 MB L2) performs few % better than NewCastle (512 KB L2) on the average for system running same frequencies of CPU, memory bus and HT bus.
Gautam said:Except for the mobile versions, yes. All of the latest 3200+'s appear to be NewCastles. The Clawhammer 3200+'s are no longer ubiquitous in the wild. There is also much speculation about a 512k 2.4GHz part for the new 3400+.
silentfire said:Guatam, no offense man but u remind me of that little annoying kid that everyone knew in elementary school that always thought the things he had were better than everyone elses and that nothing else was better, no matter what
The official finding is that the CG Clawhammer core is discontinued. OC Detective posted it in my results thread, I gotta get going though, sorry.hitechjb1 said:
I thought AMD just released a few 1.4V Mobile A64 754 CPU model 2800+, 3000+, 3200+ with 1 MB L2, which should be based on ClawHammer core.
Also there are the 3000+, 3200+, 3400+ Mobile DTR models with 1 MB L2 (ClawHammer).
Are you implying they will be gone soon?
Are they official findings?