Socket A SDRAM Performance Comparison

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Overview

With VIA’s introduction of the new KT133A Socket A chipset using SDRAM and supporting either a 200MHz or 266MHz FSB, there has been renewed interest in mainboards using SDRAM for the AMD Athlon or Duron CPU’s – Especially since DDR SDRAM is still not shipping in any sort of volume yet. You also hear a lot of advice telling you what type of memory to use: PC100, PC133 (or even ‘PC150’), CAS 2 or CAS 3. With AMD soon to be shipping the 266MHz FSB Athlon CPU’s there is also a lot of interest in them vs. the current 200MHz parts – along with advice to wait for the 266MHz FSB Athlon CPU’s. So I thought it was time to take a look at SDRAM again, comparing different memory timing settings along with different FSB speeds.

I chose a new Soyo K7VTA Pro, mainly because I have access to it and the latest BIOS’ direct from Soyo. It is not in full production yet, but since the KT133A is pretty much a drop in replacement for the KT133 I expect the test results to be a valid indication of the final release. The Soyo K7VTA series is pretty typical of current Socket A mainboards. Its features and settings pretty much match any of the other popular Mainboards, so I would expect the performance to be typical of any good Socket A Mainboard.

A couple of notes on the VIA KT133A chipset. As mentioned, it is basically a ‘drop in’ replacement for the KT133 and the only real difference is that it supports both a 100MHz and 133MHz Host Clock speed giving 200MHz and 266MHz FSB speeds. In the case of the Soyo K7VTA Pro, it is identical to the current K7VTA-B KT133 based Mainboard, other than adding two jumpers allowing you to set the FSB to either 200 or 266MHz (CPU HostClk is auto detected but can be over-ridden with the jumpers).

It appears that the KT133A is not in full production yet, and I’ve heard rumors that VIA is only achieving a 40% fill ratio on orders at this time. I’ve also heard that we may see a ‘new’ version – KT133E – that will have the same features but cost $6 to $7 less (no idea how VIA is going to do it or what changes if any in the chipset), but expected shipping wont be until well into March. It also appears that Ali is pricing the MAGiK 1 Socket A DDR chipset quite low and that VIA sees that as a threat to their market share, so lowering the price of the SDRAM chipset is one way to fight off that threat. VIA has also dropped the ball and produced a DDR chipset for Intel CPU’s before the Socket A chipset, and the VIA Socket A DDR chipset is still quite a ways away from shipping. That gives Ali a chance to gain some of the DDR Socket A market share before VIA gets their DDR chipset to market.

I was also interested in overclocking via the HostClk speeds, which seems to still be a favorite of hobbyists trying for that last bit of performance. While the Soyo K7VTA Pro doesn’t allow for stepping the HostClk in increments of 1MZ it does offer a good range of speeds to test with – including 143 / 145 / 148 / 150 / 155 / 166MHz. I managed to boot as high as 155MHz – but with errors in Win, highest stable speed was 145MHz. It appears to be a motherboard / chipset issue as I could get the same results with a good pair of PC133 CAS2 DIMM’s that I have run at 155MHz (CAS3).

So what did I test? I used an AMD Athlon 1.2GHz with the L1’s connected from AMD (allows for over-ridding the multiplier lock if the motherboard supports it). One double sided ‘PC150’ KINGMAX 128MB DIMM (note that as far as I know there is no true PC150 standard – chips are marked ‘-06’), an ATI Radeon DDR 32MB AGP video card, WD 200BB ATA/100 7200 RPM HD and Win98SE @ 1024/768-64K using 85Hz and the latest VIA 4.28 4-in-1 driver pack (used the integrated Win VIA Busmaster IDE drivers). I ran the memory at a number of different settings, used both a 200 and 266MHz FSB… even a 290MHz FSB.

First I’ll give you the complete table, as with other test I’ve run each series was run three times and rejected if the results are not within 3% (what I consider the margin of error).

The first column is how the system would perform if you used the ‘Optimized settings’ in the BIOS – not aggressive at all. The second column shows results from what I have found to be the best combo of options to enable: PC100 at CAS 2, which should be very stable and reasonably fast. I saw no reason to run those settings at CAS 3 since just about all current PC100 is CAS 2 or PC133 CAS 3 is rated for CAS 2 at 100MHz. The third column shows the results from keeping the 100MHz HostClk but setting the memory ASYNC to 133MHz and using the CAS 3 setting. The fourth is what most would consider the best setting – 133MHz memory and CAS 2. The fifth is an indication of what to expect from the 266MHz FSB CPU’s when they start shipping, and I see no reason to use anything less than PC133 CAS 2 if going that route. The sixth and last column is the best I could do using an overclocking HostClk speed (trying to keep close to 1.2GHz). Although I did not include the results, if using the 145MHz HostClk & CAS 3 the scores suffer. From what I’ve seen you need to use CAS 2 for any real gain in performance over 133MHz CAS 2.

I don’t know about you but I don’t see much difference between PC100 CAS 3 and PC133 CAS 2. Even the difference between a well setup PC100 CAS 2 200MHz FSB and a PC133 CAS 2 266MHz FSB are pretty minimal.

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