|
Advice Beginners BIOS Guide CPUs Links Mainboards Memory Network Storage Video/Sound Cards Contact Forum SiteMap Sponsors WebNews Home |
. | . |
Prices: Mainboards ABIT ASUS Chaintech Shuttle Soyo Tyan CPU Intel P4 2.4C-800 P4 2.6C-800 P4 2.8C-800 P4 3.0-800 P4 3.2-800 AMD AthlonXP XP 1700+ XP 2000+ XP 2400+ XP 2500+ XP 2700+ XP 3000+ XP 3200+ Athlon64 Athlon64 3200+ Athlon64 FX-51 Opteron Opteron 240 Opteron 242 Opteron 244 Opteron 246 Memory Corsair Crucial Kingston Mushkin OCZ |
|
|
|
LOSTCIRCUITS
|
|
| AMD's Phenom Processor - Beyond Erratum 298 | |
|
(Author: Michael Schuette, January 1, 2008) |
The Memory Subsystem
The memory subsystem of the Phenom processor is one of the key features of the CPU. On-die memory controllers should provide ample bandwidth but is bandwidth all that matters? To get started, we have the numbers from SiSoft Sandra's latest version integrated with the results form the last 3 years of CPUs coming through our labs.
Phenom numbers show the memory bandwidth at 1066 MHz memory data rate running in AOD "red" mode vs. AOD "green" mode. One caveat here is that the numbers shown for all Phenoms were acquired in MS Vista-32, the equivalent WinXP numbers are 10250 and 9649 at 1066 MHz in red and green, compared to 9939 and 9475, respectively. At 800 MHz memory frequency, there is an approximately 10% reduction in memory bandwidth. The dual Opteron numbers (**) reflect the cache-coherent non-uniform memory architecture (ccNUMA).
There is a slight difference between the red and green overdrive modes when it comes to bandwidth. Bandwidth, on the other hand, only matters to a certain degree, the days where a direct correlation between memory bandwidth and performance could be made are long over. AMD's main argument for putting the memory controller onto the CPU has been that it cuts down dramatically on DRAM access latencies. Of course, DRAM access latencies can be measured in different ways, using different algorithms that may or may not be relevant anymore for advanced technologies like, for example the case of the dual independent memory controllers of the Phenom with concurrent Read and Write capabilities. For the record, we are using Cachemem 2.65 as the only accurate tool to measure latencies but the caveat is that Cachemem is a DOS applicatoin and by definition single-threaded. As we will show, the data are 1:1 extrapolatable to SiSoft Sandra in the Vista environment but, without jumping ahead of ourselves, the "Gretchen Question" is going to be "So what?", short for "What does it really matter" as we will further show in application benchmarks.
Memory Access Latencies: Cachemem 2.65
Access latencies of the Phenom 9900 in AOD Green (transparent columns) vs. AOD Red mode (solid columns). Lower is better. As shown in the graph, there is no difference in access latencies for the different cache levels, however, as soon as the main system memory is accessed, the access latencies almost triple if AOD is not loaded and set to "code red"
Memory Access Latencies: SiSoft Sandra 2008
Access latencies of the Phenom 9900 in AOD Green (transparent columns) vs. AOD Red mode (solid columns) as measured by SiSoft Sandra. The data match what was shown above using Cachemem.
 (AMD Phenom 9600 2.3GHz (HD9600WCGDBO)) |
next page: => CPU Power Consumption =>
All advice and educational articles on LostCircuits are free, but if you feel you can, please make a small donation to us!
