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Tandy 1000 EX/HX RAM expansion... the poor man's way

Hyperfrog

Member
Joined
Aug 7, 2009
Messages
41
Location
Québec City, QC, Canada
I'm thinking about boosting the RAM of a Tandy 1000 HX without adding a DMA board. (There's one on eBay right now... The seller is asking $69 for it, and I don't even know if it is fully populated.) I think I could piggyback some static RAM chips on top of the ROM, and then route the appropriate read/write signals to those chips. I would have to do some address decoding too. If it works, it would be darn cheap. And the computer would at last become usable. However, I wonder if the BIOS would see the extra memory. How does it know/determine how much memory is installed in the computer?
 

Unknown_K

Veteran Member
Joined
Sep 11, 2003
Messages
8,554
Location
Ohio/USA
Do what I did, wait until you see a trashed HX that has the memory card installed (rear pictures showing something installed in any of the bays means you have the RAM expansion) and buy it. I got a whole system shipped for less then the RAM expansion would have cost, plus I got extra floppy drives and spare parts (my case wasn't yellowed badly but there was major physical damage to the front edge).
 

Hyperfrog

Member
Joined
Aug 7, 2009
Messages
41
Location
Québec City, QC, Canada
Do what I did, wait until you see a trashed HX that has the memory card installed (rear pictures showing something installed in any of the bays means you have the RAM expansion) and buy it.

Thanks for the suggestion, but I don't know where to find a trashed HX (or EX)... I could wait for several months, or even years, before one fitted with the DMA/RAM card shows up on eBay. And then, it would most probably be from a seller located in the USA. If he/she agrees to ship the computer to Canada -- the probability of which is below 50% --, this is going to cost me about $40 in shipping alone... And if I pay more than $20 for the computer, I will have to pay customs duties and taxes. Supposing the seller knows the DMA/RAM card is not easy to find, or if any other bidder wants the computer for this very reason, I certainly won't get the computer for $10.

Besides, making a custom upgrade to an old computer is both fun and rewarding. So if somebody could answer my original question... How does the BIOS know/determine how much memory is installed in the computer?
 

geoffm3

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Joined
Oct 9, 2009
Messages
1,260
Location
Huntsville, AL
Dunno... I would guess you'd probably have to dig into the BIOS code some. On the ram expander I just got there's a jumper that's used to set how many banks are populated with RAM, and that's reflected in the memory count at system startup. I assume then that the system probably reads some register on the ram expander to see if it's present and how many banks are available.
 
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