Different CPU and system platforms (940, 754, 939)
There are two main platforms, namely CPU's with 754 and 939 sockets (we can skip the third one 940 for now). The 754 and 939 literally refer to the pin count of the CPU/socket, but ther are implications on system cost, performance, scalability into the future, ....
- 754 can be considered for price/performance and early adaption
- 939 can be considered for higher end, its scalability and future compatibility of motherboard features and CPU (price and yield) into the future.
- Theoretically, a 939 always delivers better peformance than a 754, especially on memory bandwidth and memory intensive applications, if price-performance is not a major consideration factor.
- Both 754 and 939 have L2 cache size 512 KB or 1 MB, eventually to 2 MB (for 939).
- The total system bandwidth (memory + HT) is about two times that of XP system for 754, four times for 939.
- A major difference between 754 and 939 is the memory bus and memory bandwidth.
... 128-bit dual channel memory bus for 939 and 64-bit for 754.
... Non ECC memory modules supported by both 939 and 754 (940 requires ECC memory).
... Effective memory bandwidth of 939 is estimated to be 80+% higher than that of 754.
64-bit and 128-bit are memory data bus width for 754 and 939/940 respectively. Actual memory bus width (with ECC bit) is
- 64 bit + 8 bit ECC, total 72 bit for 754
- 128 bit + 16 bit ECC, total 144 bit for 939/940
Memory module (for 754 and 939 platforms)
Nice thing about 754 and 939 CPU's is that they can work, for non-mission critical system, with existing non-ECC DDR 400/500 (PC 3200/4000) memory modules that most of us have.
Opteron, A64 Fx with Socket 940 require ECC memory modules.
PC3200 or DDR 400 is rated at 200 MHz, max bandwidth = 200 x 2 x 8 = 3200 MB/s
PC3500 or DDR 438 is rated at 219 MHz, max bandwidth = 219 x 2 x 8 = 3500 MB/s
PC3700 or DDR 462 is rated at 231 MHz, max bandwidth = 231 x 2 x 8 = 3700 MB/s
PC4000 or DDR 500 is rated at 250 MHz, max bandwidth = 250 x 2 x 8 = 4000 MB/s
Towards year end of 2005, A64 platforms may move to DDR2 memory module (discussed in other posts in this thread) which would require new motherboards, maybe new CPU socket (not clear as of May 04).
