Wow, that is a strange arrangement indeed. I suppose it is to get just enough video memory for say 1024 x 768 with 24bit color.

Tiido wrote on 2021-01-14, 14:44:

Wow, that is a strange arrangement indeed. I suppose it is to get just enough video memory for say 1024 x 768 with 24bit color.

Looks like someone grabbed whatever was left in the back of the drawer and jammed it in that card.

Might have been enough video memory for 1024 x 768-24b, but I don't think the 108Mhz pixel clock in the TGUI9440-3 was powerful enough for that. I think it may have tapped out @ 1076x768-16b interlaced.

https://datasheet.datasheetarchive.com/origin … /DSA-639114.pdf

douglar wrote on 2021-01-14, 15:09:

Looks like someone grabbed whatever was left in the back of the drawer and jammed it in that card.

Yup, looks like that, and it didn't have any impact. I removed those 2 chips that are to the right of the card (the vertical ones) and it's still working and still reporting 1mb of ram, even if there are still 3 x 512kb chips installed, which is weird. I'll keep removing them and see where it goes.

Edit: Ok, some progress. I removed the top left one, and now the card reports 512kb of ram. So in the 2 remaining chips there may be a faulty one, or there may be a socket that's not used in that combination. I'll keep checking.

douglar wrote on 2021-01-14, 15:09:

Might have been enough video memory for 1024 x 768-24b, but I don't think the 108Mhz pixel clock in the TGUI9440-3 was powerful enough for that. I think it may have tapped out @ 1076x768-16b interlaced.

https://datasheet.datasheetarchive.com/origin … /DSA-639114.pdf

Ok, indeed it cannot do 24bit color. 1024x768 @ 60Hz is just under half of 108MHz, but since memory bus is limited by DRAM speed, 1024x786 @ 60Hz 16bit colo is just about maximum possible to do and datasheet seems to agree too. Later cards/chipsets with 64bit bus can do more with same speed chips...

Tiido wrote on 2021-01-14, 17:38:

Ok, indeed it cannot do 24bit color. 1024x768 @ 60Hz is just under half of 108MHz, but since memory bus is limited by DRAM speed, 1024x786 @ 60Hz 16bit colo is just about maximum possible to do and datasheet seems to agree too. Later cards/chipsets with 64bit bus can do more with same speed chips...

Is there a good chart or calculator somewhere that lists the ramdac speed & memory bandwidth necessary for a given resolution x colour depth x refresh rate?

You get the approximate pixel clock requirement by (X res * Y res * Refresh rate Hz * blanking overhead). 1.3 is a good blanking overhead figure. The actual amount of pixels per line is longer than what is visible and there are a small handful of more lines total, the excess is blanking+sync area. This was done to allow typical cheapest CRT implementation to work with no visual distortions.

For memory bandwidth you multiply that number by color depth . 0.5 for 16 color, 1 for 256 color, 2 for 32768/65536 colors, 3 or 4 for 24bit. Some cards use 4 bytes per pixel for truecolor, because it is faster than fetching 3 bytes per pixel, and is easier for CPU to process too but it requires more VRAM as there's one wasted byte every pixel.