Memory Bandwidth vs. Latency Timings

After playing with several DDR DIMM's intended for Pentium 4 C systems on both our Socket 754 and Socket 939 Athlon64 platforms, I think it's safe to say that they behave very much like AthlonXP systems. Most Athlon64 systems cannot easily reach the same motherboard speeds as their Intel counter parts, and this means the memory cannot make up for the high latencies with pure memory bandwidth/speed.

In fact, it seems that most high speed DIMM's do not run very well on Athlon64 systems. Often, the RAM is unable to reach its advertised speed, even though the motherboard has been tested higher.

Maximum Overclocked Speeds - PCstats Results
*AMD System Results*	Timings	Max Speed	Ranking
OCZ PC3700 Gold Rev2	2-3-2-6	486 MHz
OCZ PC3200 Plat LTD Ed	2-2-2-5	480 MHz
OCZ PC3500EB Platinum	2.5-2-2-5	460 MHz
Mushkin PC3200 Special Edition	2-2-2-5	454 MHz
Corsair TwinX3200XL	2-2-2-5	450 MHz
PMI PC4200-512DG	2-3-3-6	434 MHz
Buffalo Firestix FSX5000V	3-4-4-8	424 MHz
Corsair TwinX1024-4400PT	3-4-4-8	410 MHz
OCZ PC4000EL Gold	2.5-4-4-7	406 MHz
*Intel System Results*	Timings	Max Speed	Ranking
Corsair TwinX1024-4400PT	3-4-4-8	550 MHz
OCZ PC4200 EL	2.5-4-4-7	542 MHz
OCZ PC4000EL Gold	2.5-4-4-7	536 MHz
PMI PC4200-512DG	3-4-4-8	526 MHz
Buffalo Firestix FSX5000V	3-4-4-8	522 MHz
Corsair TwinX3200XL	2.5-3-3-7	520 MHz
GeIL PC4000 Platinum	2.5-4-4-7	520 MHz
Corsair TwinX4000PRO	3-4-4-8	520 MHz
Corsair TwinX4000	3-4-4-8	516 MHz
OCZ PC3200 Plat LTD Ed	2-2-2-5	480 MHz
Mushkin PC3200 Special Edition	2-2-2-5	472 MHz
OCZ PC3500EB Platinum	2.5-2-2-5	460 MHz
OCZ PC3700 Gold Rev2	2.5-4-4-7	460 MHz

As you can see from the above table of results, the (slower rated) low latency memory can actually reach a higher overall speed, while keeping tighter timings. All the high speed DIMM's based on Hynix memory do quite poorly, topping out at an unimpressive 217 MHz. Unless the Athlon64 architecture changes drastically in the next little while, make sure you buy low latency memory (2-2-2-5) for you Athlon64 system just as you would for an AthlonXP system!

While bandwidth is still very important to the Intel Pentium 4 processor, it's not as important as it once was in the days of the i845PE, and single channel memory controllers. Thanks to the i865PE/i875P's dual channel memory controller things are much brighter. On average, the system with the memory running at 400 MHz (5:4 memory divider enabled) with aggressive memory timings performed 2-3% faster than the system using high speed memory with loose timings.

While that may not seem like a lot to most people, it can make a world of a difference to the enthusiast, especially if you're gunning for that high score in a clan match where every FPS counts.

It seems as if all the large memory manufacturers/suppliers are afraid to lose face by not pumping out high speed memory modules with lax memory timings just so they can list them in their product lines. Many enthusiasts I know, tend to favour slower memory which allows them to run aggressive timings however.

One might say that the benchmarks we used were stacked against memory that uses conservative timings, but if you think about it, games and simple 2D applications are the programs that most consumers run where speedy performance really is important. That's why we ran the benchmarks we did; office environments with their servers or work station PC are more interested in stability, and overclocking has an element of risk involved for both hardware and software.

Athlon64 based systems act a lot like the 800 MHz FSB Pentium 4 processors in regard to their memory bandwidth and timings when overclocked.... but they are by no means interchangeable. From the updated results shown above, AMD K8 processors are clearly much more sensitive to lower latency DDR RAM, and justifiably prefer it. Much like the AMD K7 processors before it, Athlon64 processors produced the best results when overclocked with lower latency DDR memory.

If you're in the market for new memory for your Intel Pentium 4 system and you're only thinking about gaming performance, then you're best bet is to get DDR which is rated to run aggressive timings. Some examples include Mushkin's PC3500 Level II which is rated to run 2-2-2-5 at 217 MHz FSB or Corair's TwinX-3200LL which are rated for 2-2-2-5 at 200 MHz.

If you're a newbie/novice overclocker and would prefer to buy something that takes a little less work while still producing good numbers on your Pentium 4 system, then by all means get some of the high speed DIMM's that are available on the market. They're not quite as fast as the low latency modules as we've shown, but they're much easier to set up. Now for AMD systems; because the AthlonXP cannot hit as high speeds as the Pentium 4 in general, it is always best to pair an AMD processor (AthlonXP or Athlon64) with nice low latency memory for the best results.

2-3% Improvement