April 2009 Archives

TRS-80 Model 4P RAM Upgrade


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.

eBay and Zip Chips

| No Comments

Ah, the Zip Chip. For those unfamiliar, the Zip Chip was a popular CPU accelerator solution for the Apple II series of machines, which bumped the default 1MHz CPU speed anywhere from 4MHz to 8MHz depending on the upgrade chip model. These chips are understandably still in demand and devilishly difficult to source. Unfortunately, when one does run across one of these treasures, it may turn out not to be what you’d bargained for.


I’ve come across a couple of these on eBay, and actually wound up buying a “phony” one last month (the other was also a phony, but the auction was more transparent to that fact). To be clear though, it wasn’t intentionally sold to deceive. Likely, the scenario played out along these lines:

  1. Twenty years ago, an Apple IIe owner buys a new Zip Chip. He installs the chip in his Apple IIe and removes the old 1MHz CPU, placing it in the same foam block the Zip Chip was housed in for safekeeping. He then places the old 1MHz CPU, manual, and diskette back in the original Zip box and stores it on the shelf. (Same thing I would have done.)

  2. Over the years, the Apple IIe is sold, passed on or otherwise disposed of with the Zip Chip still installed. The original Zip Chip box finds its way to another owner, probably mixed in with other Apple II software, and is placed on eBay. Hey, it’s got a CPU in the box - it must be complete!

  3. Gullible individual (me) buys it, finding a bog standard 1MHz CPU (a Rockwell 65C02 338-6503 pulled from a stock IIe).


In closing, make absolutely certain the Zip Chip in a given box is the real thing - there’s a very high probability it contains nothing more than leftovers from a previous upgrade. It’s becoming more and more apparent that the best way to get a Zip Chip is to find an Apple II with one already installed.

About this Archive

This page is an archive of entries from April 2009 listed from newest to oldest.

March 2009 is the previous archive.

May 2009 is the next archive.

Find recent content on the main index or look in the archives to find all content.