Memory Timings Analysis

Review by Harry Lam on 05.16.03
Test Ram provided by Crucial, MSRP: $26.00 (per stick)

Introduction:

The typical BIOS usually offers a varying number of settings directly related to memory: everything from timings to clock speeds.  It's generally known that smaller and more aggressive timings combined with higher clock speeds leads to higher performance, but for the most part, the increase in performance from tweaking each individual setting is relatively unknown.  Perhaps in a bit too ambitious move, I set out to examine the impact of each individual memory timing and clock speed on overall performance.  The article that follows contains my experiences in this "memory benchmarking adventure" in conjunction with Crucial's PC2700 DDR RAM (and also gives a relatively good picture to the limits of this memory).

I would recommend that anyone interested in learning more about memory timings take a look at this site.  It gives a pretty good technical intro to memory timings.

Testing/Methodology:

Motherboard Selection:
I decided to use the Soyo SY-P4X400 for testing, due to the flexibility of its BIOS in relation with memory timings, allowing me to change 10 different memory-related settings.

Benchmark:
To save on time and testing (all of the testing occurred over a 5 day period, with several hours of testing in each day), I picked only one benchmark: the memory test on SiSoft Sandra Professional 2003 v9.41 (SP1).  I did notice that the initial few benchmarks on any configuration usually were significantly higher or lower than the "steady-state" score (the stabilized value that comes up after successive test runs of the benchmark in a row).  To compensate for this, I selected the median score after the scores stabilized from successive benchmarks.

Depth:
I decided that 4,608 different combinations of memory timings on my particular test bench was a tad bit too much testing, and created a methodology which would get a look at the general increasing performance of memory timings but had the downside of having an uneven number of data points for timings that were deemed "less-significant (more on this later).  This methodology simplified the number of combinations down to a mere 289 combinations (which actually still is extremely time consuming, considering that the test computer has to be reboot after testing each combination).

I established Memory Speed (100, 133, 166), CAS Latency (3.0, 2.5, 2.0, 1.5), and Bank Interleave (Disabled, 2 Bank, 4 Bank) as the primary criterion for my benchmarking (as these usually are the settings that are most emphasized).  The "less significant" memory timings (Trp, Tras, Trcd, DRAM Command Rate, DRAM Burst Length, Write Recovery Time, and DRAM Access Time) as a result received a less thorough testing.

The general testing methodology is as follows:

All combinations of Memory Speed, CAS Latency, and Bank Interleave were tested at the least aggressive memory timings, and once that was complete, I changed the first of the "less significant" memory timings to a more aggressive value (Trp was changed from 3T to 2T).  I then repeated benchmarks for all possible combinations of CAS Latencies, and Bank Interleaves based on this new timing (12 total combinations).  Once this was complete, I changed the value of the next "less significant" memory timing (Tras), and repeated another set of 12 combinations (keep in mind, I left Trp at 2T, the most "optimized" value).  This process was repeated for each "less significant" memory timing, and then the entire set (of 96 different combinations) was repeated at an increased clock speed (for a total of 289 different combinations).

As I stated earlier, this results in an uneven number of data points.  For example Trp had 36 data points at 3T compared with 252 data points at 2T, and the reverse is true for DRAM Access time (252 to 36).

Test RAM:

Crucial was gracious enough to send me two 128MB sticks of their PC2700 solution to aid my testing.

Crucial 128MB PC2700 DDR RAM: Part #CT1664Z355:

Note that I did not adjust the DRAM voltage at all on my motherboard, so the potential for more aggressive timings is present.

Test Bench:

Intel P4 2.4 Ghz, 400Mhz FSB, 512K L2 Cache CPU
Soyo SY-P4X400 Dragon Ultra Platinum
ATi Radeon AIW Video Card
Crucial 256 MB PC2700 DDR RAM (Provided by Crucial)
Maxtor DiamondMax Plus 60GB D740X Hard Drive
Windows XP Professional Service Pack 1

Most readers will want to skip past the next page, as what follows is the full data table of our testing (all 289 data points).  If you prefer, you can download the following data table as an Excel spreadsheet.