Updating TOS to version 1.04

After finishing the drive swap mod on my Atari 1040 STF I continued browsing the Atari forum’s hardware section and found a post/guide on how to update the operating software. In general, updating the OS is advisable as newer versions may contain bug fixes, security updates and increased I/O compatibility. The same goes for my Atari. The last available version for my machine, 1.04 a.k.a. Rainbow TOS, contains all of the above and is found to be faster overall.

On the Atari, the OS is stored on two or in my case six ROM (Read Only Memory) chips. As the name indicates, writing to ROM chips is not possible so they have to be replaced with chips containing the newer OS. While it is possible to buy a “ready to go” upgrade package it is also possible to go the DIY route and prepare the chips yourself. I opted for the latter as it is much more fun, educational and gives a real sense of achievement when finished.

After two weeks I had everything I needed and was able to continue the project.

Before writing the OS image it had to be split in to six parts using ROMSPLIT. A physical machine or emulator is needed to run ROMSPLIT as it is build specifically for the Atari. I used the STEEM emulator which can be found here: http://steem.atari.st/download.htm. After splitting the image I was left with the following files:

Now it was time to write the different parts to the EPROM’s. This process is fairly straight forward as it is nothing more than connecting the programmer, plugging in the EPROM, launching the programmer software and selecting the correct IC, opening the file to write and pressing write. After each chip I took a piece of electrical tape and stuck it over the glass window to prevent the chip from being erased. I also wrote the corresponding part name on the chip.

After preparing the EPROM’s came replacing the old ROM’s. At first I thought this would super easy but I could not figure out where to put which chip. According to the Atari forum the correct places were indicated on the motherboard but for some reason my Atari only mentioned U2 to U7.

Luckily I was not the only one having this problem and I soon found the correct place for each chip. For future reference here is what worked for me (and others):

EPROM LabelSocket


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