performance DROP when adding RAM?

OK, this is weird:

When I got my Inspiron 1000, I ran 3dMark2001SE out of morbid curiosity. I got 1225 or so. Yesterday I added a 256Mb PC-3200 SO-DIMM (yes I know it only needs PC-2100, but the 3200 had the best price when I ordered). This increases the video memory from 32Mb to 64Mb.

Now when I re-run 3dMark, I get 1010 or so. I pulled the extra RAM, and I'm back to 1225. I ran the test several times just to make sure - I always get about 1225 w/o extra RAM, and about 1010 with. That's 17% DROP in performance.

This makes no sense to me; really I don't think adding RAM should change the 3dMark2001 score at all, and it certainly shouldn't hurt performance.

Anyone know why this would be?

Dave

 

What size is the other RAM module? If it is 128 mb then the DDR functionality would be disabled. The fact that it is pc-3200 mich screw things up, as the motherboard is not meant to deal with that speed. It would benefit you to see what happens when you use actual Pc-2100.

 

The RAM built-in to the notebook is 256Mb as well. I think you are thinking of dual-channel or bank interleaving possibly being disabled if the memory modules aren't the same size; DDR couldn't be disabled.

But I think you may have led me to the problem. PC-Wizard 2004 says the DIMM I added is a single bank DIMM, while the on-board RAM is double bank. Thus bank interleave is disabled with the RAM added. This accounts for the performance drop; it seems to affect the graphics much more, but both Sandra and PC-Wizard show a memory bandwith drop with the extra RAM:

Sandra: 5615 int/2939 float w/o RAM, 5525 int/2950 float w/ RAM
PC-Wizard: 361 float/818 int/173 latency w/o RAM, 347 float/792 int/179 latency w/RAM

PC-Wizard's DirectX benchmark also shows a performance drop similar to 3dMark.

I'm surprised this small bandwidth and latency drop is causing such a large drop in 3D performance, but there it is...

Now I just have to decide if I care enough to return this RAM and get something else.

 

well, now I'm not so sure. I pulled the RAM again, and sure enough, PC-Wizard now shows the remaining RAM module as being double-banked. BUT it still shows interleaving as being 1-way.

However, PC-Wizard may not accurately report everything about this system. I guess I'm most inclined to believe it's conclusion that the on-board RAM is double-bank and my add-in module is single-bank. I do know that some chipsets are really sensitive to single- vs double-banked RAM, the i865/i875 being a perfect example. I've no idea about the SiS M650 used in this notebook, but it makes sense that it would as well.

 

See if you can change the video memory size down to 32 manually. Ive heard from sites that bumping up the memory given can actually slow down the cpu rather than speed it up.

 

No, the video memory size can't be adjusted. It's fixed at 32Mb if 256Mb of RAM is installed, and 64Mb if 512Mb is installed. It's even spec'd this way on SiS's spec sheet for the M650, so I don't think even Dell could adjust it if they wanted to.

At this point, my bigger concern is the apparent bandwidth drop and slightly increased latency with the added RAM installed. Now that I have a probable answer to satisfy my curiosity, I'm probably just going to ignore it.