ET6000 memory size facts and fiction

Information for Tseng Chipset Users : ET6000 memory size facts and fiction
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## 10. ET6000 memory size facts and fiction

The ET6000 uses a special kind of video memory called MDRAM (multi-bank DRAM). It may have a non-power-of-two amount of MDRAM: 2.25 or even 4.50 MB. Especially 2.25 MB MDRAM is popular, since this can support 1024x768 at 24bpp without needing 4MB of RAM.

There are a few less intuitive problems with this.

First of all, All memory above the 4 MB limit is a waste of money, because the ET6000 cannot use this memory for anything at all. There are boards with 4.5 MB around, but that extra 0.5 MB is a waste. The ET6000 can only refresh 4 MB of (M)DRAM (refresh register). It can only access 64 banks of 64KB in VGA mode (bank select register). All accelerated commands use a 22-bit address (=4MB) inside the video memory. You get the idea...

And Secondly (more importantly): you may not have 2.25 MB at all! There have been several reports about ET6000 cards that were sold with (supposedly) 2.25 MB of MDRAM, but which turned out to be standard 2MB MDRAM cards. People have been having trouble with these all along, since sometimes the X-server used to detect this as 2.25 MB (or even 2.5 MB) due to internal chip design and also due to faulty BIOSs. This memory detection problem has been fixed now, and the server should detect the correct amount of memory.

Do NOT define the amount of memory in the XF86Config yourself, unless you are absolutely sure about the amount. There is a simple way to determine the amount of MDRAM on your card beyond doubt.

Look at the video card. There is one large chip with 204 pins on it, which is the ET6000. One socketed rectangular chip, mostly with a sticker on it,is the BIOS. The remaining chips are (mostly) 2 or 4 other large square chips on it with the following markings:

MDRAM MD9xy ("xy" is a two-digit number) SJ-5-100 (this may differ, but it will have the same layout)

and a nice logo next to all that with 4 diamonds and the name "MoSys" underneath.

The "xy" number tells you how much MEGABITS are in that one chip.

The amount of RAM on the card is then:

("xy" * number_of_MDRAM_chips) / 8 Mbytes

On my board, there are two MD908 chips, which means I have

(08 * 2) / 8 = 2 MB of MDRAM.

Boards with two MD909 chips have 2.25 MB, etc.

Current MDRAM chips are MD904, MD906, MD908, MD909, MD910, MD916, MD918 and MD920.

Information for Tseng Chipset Users : ET6000 memory size facts and fiction
Previous: Acceleration issues
Next: ET6000 memory bandwidth hype and the impact on video modes