Out of Memory?

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How I upgraded the RAM on the Atari 400
by Joseph Burke

August 3, 2005

First, some background. Back in 1979, Atari released the 400/800 line of home computers to much fanfare. It was the first machine to use sprites in games (player-missile graphics in Atari-speak). The 800 was released in memory configurations ranging from 8k-48k, the 400 with either 8k or 16k. Some other differences between the two machines included an IBM Selectric typewriter inspired keyboard on the 800 as opposed to the cheaper (and harder to use) flat membrane keyboard on the 400. The 800 also had two cartridge slots versus one on the 400. The 400 also lacks a video out for connecting to monitors, relying solely on an RF modulator for output to a television. Both have four joystick ports making them a gamers' dream, but not every game utilized them. The Atari joystick ports are very fast, however, and many hardware devices were released that utilized them instead of the larger SIO port. It was much less expensive to buy a modem that plugged into the joystick ports than to buy an 850 interface and a modem that connected via an RS-232 port. Back then floppy drives were expensive, so many Atari users used a cassette player for storage so the difference in memory size didn't make much difference until the price of floppy drives came down and more and more Atari users started buying them. 400 owners, soon found out that their machines couldn't handle floppies due to having too little RAM and were forced to either upgrade to an 800 or send their 400 out to be upgraded, an expensive and time consuming process.

My first Atari computer back in the middle 80's was an 800XL with 64k. After a while, I bought a 48k 800 for running those programs that even the Translator disk couldn't handle, so I never knew the limitations of running a machine with less than 48k for a long time. When a 16k 400 became available to me, I grabbed it, brought it home, and quickly found out how limiting 16k can be, especially if you want to run a floppy drive. I wanted to upgrade the memory, but every person I talked to and every magazine article I read declared the 400 not upgradeable without buying an expensive upgrade and sending your machine out to have it installed.

I was not deterred, however, and proceeded to open up my machine to see what could be done about it. Getting the beige, plastic shell open was easy enough. I was then faced with the monolithic aluminum shell that provides RFI insulation for the mainboard. Once I got past my initial fear about proceeding further, however, it was relatively easy. I still needed a memory board to replace my old one with, though, so I took a trip to my local Atari dealer who happened to have a 32k board for the 800 collecting dust on the shelf, so I bought it and the experiment began in earnest.

We need to go through a little history, here, to give you more of a feel for the Atari scene back in those days. In the early to middle 80's, it was a common practice for users to pull out one of the memory boards in the 800 and replace it with a hardware device of some kind. Real time clocks, machine language monitors, 80 column cards and others were available that fit these slots. To add these, though, meant sacrificing some memory, so memory boards were released with extra RAM on them so you could still install your device and have 48k. The 32k board that I bought is just such a product. Installing this in an 800 along with a standard 16k board gives you 48k and frees up a slot for devices.

Upgrading the RAM on an 800 involves pulling out the memory boards under the cover and replacing them with boards with a higher memory capacity, but the 400 doesn't have memory boards under the cover leaving many owners feeling that they are stuck with whatever memory came with their machine. DOS is relatively big, so you can't connect a floppy to a 400 until you do something about the memory. Good news, though. The 400 can be upgraded, but it's a little bit trickier.

First of all, the 400 only has one memory slot onboard as opposed to the 3 on the 800. This isn't as limiting a factor as you would think, though. Now for the tricky bit. What you have to do is disassemble your 400 to get at the memory slot. It is housed underneath the heavy aluminum shell that I mentioned earlier.You can do this with just a screwdriver. Once you have the aluminum shell detached, you now have access to your lone memory slot. Simply remove the stock memory board and replace it with one of a higher capacity. There is another slot under there, which is also present on the 800, but that is not for memory. It is designed for testing and troubleshooting by a technician, so ignore it. Reassemble it all, power it on and in Basic type PRINT FRE(0) to see your new memory size. I have been running a 400 with a 32k board designed for the 800 for some time now, and it works great with no other modifications being necessary.

I hope this helps someone with a 400 who wants to run DOS and has access to a memory board with more than 16k. Maybe you can find someone in the Atari community with the skill to upgrade your stock boards or who has an upgraded board they are willing to part with.