Influence of cache L2
First off in this area, we wanted to know what would be the performance gain of the 4MB of unified cache L2 compared to 2 MB. To do so, we compared a Conroe (4 MB) and an Allendale (2 MB) both clocked at 2.13 GHz:
As usual, gains were variable depending on the application. We reached 7.2% with WinRAR, 6.2% in Pacific Fighters and 4.8% in Far Cry, which is appreciable. There are, however, some applications, in which gains are only 1%, or even less, for example 0.2% with 3ds max.
These gains are relatively comparable to those obtained with the increase from 512 KB to 1 MB of cache per core on the Athlon 64 X2.
Influence of DDR2 frequency and timings
What is the influence of DDR2 on the Core 2 Duo? Because Intel has once again improved the hardware prefetch to restrict penalties due to memory access, we can think that the impact will be reduced. This is something that we wanted to verify.
To do so, we measured performances in four areas. First, we focused on a reading bandwidth test and a latency cycle with ScienceMark. These results are expressed in MB and in number of cycles, respectively. Finally, two applicative tests complete the above results with WinRAR and Far Cry, which are especially dependent on memory sub system speed.
With a FSB of 1066, the theoretical maximum bus bandwidth is 8,533 MB/s. Even if these values aren´t reached here in practice, it´s certain that this is restrictive for memories such as DDR2-1066, which have up to 8.5 GB /s of bandwidth in dual channel. This doesn´t stop the DDR2-1066 from bringing a bandwidth gain. The gap is 12% compared to the poorest adjustment that is DDR2-533 in 4-4-4-12.
For latency, there was a rather significant gap between the DDR2-1067 and other types of memory. One possibility is that this is due to the asynchronous FSB frequency and memory bus in DDR2-667 and DDR2-800, whereas in DDR2-1067, the memory bus works exactly at two times the FSB frequency.
We move now to more "practical" results. We begin with compression time in WinRAR. As you can see, DDR2-1067 in CL5 is 15% faster than DDR2-533 in CL4. DDR2-667 CL4, DDR2-800 CL5 and DDR2-533 CL3 are quite close.
With Far Cry, the gap is smaller because the DDR2-1067´s gain is only 8.9%. Here again the performances of the DDR2-667 CL4, DDR2-800 CL5 and DDR2-533 CL3 trio are very close.
What about the behaviour of the Core 2 Duo compared to DDR2 and AMD? For this test we looked at the impact of timings and frequency on the two platforms. We indicated the percentages of performances reached compared to the best adjustment:
The results speak for themselves. With AM2, DDR2-533 CL4 is only at 83 and 87% of the performance level of DDR2-800 CL4, whereas with the Core 2 Duo results increase to 91% and 84%. The impact of a slower memory is half as significant for the Core 2 Duo as for the Athlon 64 X2.
Influence of FSB
We also wanted to know what was the influence of FSB on the performance of the Core 2 Duo. To do so, we made a series of tests always at 2.4 GHz but with the following two configurations: 9x266 and 7x342 MHz.
The first thing to notice is memory bandwidth that strongly increases and benefits more from the DDR frequency increase. FSB restricted the latter in the previous test.
However in FSB1370, DDR2-1026 CL5 is in finally at a comparable level to DDR2-684 in CL3, because of the combined action of frequency and a little help coming from synchronicity.
In FSB1600, there are not many choices possible: DDR2-600, 800, 1000, 1066, 1200, etc. ...but over DDR2-800, strangely the motherboard no longer boots. The fastest adjustment possible was DDR2-800 in 4-4-4 and performances obtained are better than DDR2-855 4-4-4 in FSB1370 because of synchronicity.
In the end, FSB doesn´t have a big influence on performances and there is not much gain in reducing the coefficient for its benefit. More than the highest possible FSB and DDR speed; we will try to have optimum performances and find the best adjustments combining a high FSB, aggressive timings and DDR running at 1x or 2x of the FSB speed. Either way, except for several adjustments performances were relatively close.
