Last month I mentioned my desire to upgrade the RAM in my TRS-80 Model 4P to 128KB. To that end, I ordered a TRS-80 Model 4 RAM upgrade kit from computernews80 ($28, available via their eBay store).
The upgrade comes as a nicely packaged kit of eight Tandy-badged 8040665 64K x 1 DRAMs (essentially 4164 DRAMs with a Tandy part number) carefully inserted in a anti-static foam block. It also includes detailed installation instructions covering all revisions of the Model 4/4P series as well as a 5.25” memory test/diagnostic diskette.
The installation process was quite easy on my gate-array Model 4P and only took about ten minutes - I spent a little more time as I took this opportunity to clean the case plastics in the bathtub. In a nutshell, open the case, remove the logic carrier pan and simply plug the eight chips into the empty sockets on the logic board. Next, move the memory enable jumper from the E2/E3 pins to E1/E2.
And that pretty much sums it up - the additional 64KB works, allows for RAM disk capability as well as extended RAM for certain applications that can take advantage of it. At $28, the price may seem a bit high given current RAM prices for modern machines, but you do get a very nicely put together kit with authentic Tandy DRAMs. I couldn’t help but smile as I upgraded a roughly 25 year-old machine with “new” RAM (with 1984 date codes) in 2009. Fun stuff!
Next up I hope to find a source for CP/M for the Model 4 - it will be fun to see how the experience compares to other luggable CP/M machines of the period such as the Kaypro or Osborne.