ASCIIMath creating images

Wednesday, June 8, 2011

Ancient history: my first Amiga mod

Currently, I am in the process of cleaning up my collection of old computers. I came across one of the pieces I'm still quite attached to (since it was my main computer for a considerable while): my Amiga - one of those before they had model numbers (now called the Amiga 1000). One of the reasons it is special to me is because it was the first major surgery I performed on a computer, which furthermore _had_ to work since I didn't have any other computer at that time. The hack? Expand it to have 1 Megabyte of RAM.

The stock A1000 came with only 256k of RAM, and was quite famous at the time for being able to multitask in that limited environment. However, noone ever left it at that. Almost every A1000 has the added 256k expansion in the front slot, for a more usable 512k. From Commodore's perspective, that was as much as once could expand the A1000 without using the external side expansion slot.

However, if you had the guts to do it you could add another 512k inside the A1000 without a PCB.  This involved piggybacking RAM chips on the existing onboard RAM, and hacking RAS, CAS, and address lines to select the chips appropriately. This is what I did - and I have no idea where the instructions came from. A quick search of Aminet and the Fish Disk index didn't find anything. The hack was done in about 1991, if I remember correctly.

This is the inside of the A1000, with the RF shield removed. Nothing special to see except for one extra small green wire attached to the WOM (kickstart) daughterboard.
Underneath the daugtherboard, it's a bit more messy.  Note that I did label all the wires, but instead of heat-shrink tubing I used bits of electrical tape for insulation.
This shows the detail of 2 RAM chips piggybacked onto the original RAM, with a socket.
Now this is truly ugly. Obviously, I had no idea about proper electronic construction back then.  Yes, these are resistors directly soldered to IC pins.
But, 20 years later, it still works! The screen titlebar actually says "896456 free memory'
This is the only repair I have to do. The wire on the daughterboard is close to breaking off. 
How much I have learned since then... But the lesson I learned is not to be afraid of modding hardware!