Ruud
Veteran Member
I have this XT board that can handle 1 MB of RAM. By accident I found a picture on Modem7's page. The photo is part of an entry on http://minuszerodegrees.net/xt_clone_bios/xt_clone_bios.htm, look for "Motherboard: Unbranded XT clone (CPU: V20)". As you can see it doesn't mention the capability of handling 1 MB of RAM, maybe for the simple reason that fact was unknown.
How do I know it can handle 1 MB? Because it in my case the board has eight 414256 DRAMs on the board plus four 41256s for parity AND the BIOS counts up to 1 MB.
I looked on the internet for more info but none found so far. In fact I looked for software that can use the extra RAM but no luck here as well. I started to disassemble the BIOS and soon had the idea that a register at IO address 0E0h was used to select the extra RAM. But then I also ran into the registers 70h and 90h and so far I have no idea what they are used for. I hope time (or on of you) will tell.
I attached a photo of my board plus a ZIP containing the JUKO V2.30 BIOS.
How do I know it can handle 1 MB? Because it in my case the board has eight 414256 DRAMs on the board plus four 41256s for parity AND the BIOS counts up to 1 MB.
I looked on the internet for more info but none found so far. In fact I looked for software that can use the extra RAM but no luck here as well. I started to disassemble the BIOS and soon had the idea that a register at IO address 0E0h was used to select the extra RAM. But then I also ran into the registers 70h and 90h and so far I have no idea what they are used for. I hope time (or on of you) will tell.
I attached a photo of my board plus a ZIP containing the JUKO V2.30 BIOS.