Macintosh Plus – Upgrade

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With a lovely Macintosh Plus all things seem possible… Well perhaps not so much with only 1Mb RAM. Inside the Mac you can see the existing 4 X 256Kb 30ppin simms: (Rather dusty in this case!)

There is the layout:

It is really easy to upgrade the memory you would think. Well yeah. Not TOO bad but plug and play? Na! Finding the memory modules was easy, I had 4 1Mb SIMMS in a box and they seemed to be the correct type. The Macintosh Plus has specific RAM requirements:

DRAM Speed 150 ns
SIMM Type 30-pin
Supported Sizes in 256K, 1Mb
Maximum DRAM 4 MB

I guess because the memory options are limited and likely dont change oftern and also an engineer would typically be booked to do it… There is a set of 2 resistors that control the memory allocation. These have to be either be removed or left depending on the setup.

In my case I snipped off the R8 resistor and taped it up. Essentailly removing both resistors.

The distribution of SIMMs has to be specific. The following table describes that:

1 MbRequires 4 x 256Kb SIMMS
Leave resistor R8
Leave resistor R9
2.5 MbInstall 2 X 1Mb SIMMS into Bank A
Install 2 X 1Mb SIMMS into Bank A
Remove resistor R8
Remove resistor R9
4 MbInstall 4 X 1Mb SIMMS into accross both banks
Remove resistor R8
Remove resistor R9

Notice that the Plus does not support 2Mb of RAM oddly, only 2.5Mb RAM. Remindes me of the Frankenstein-style RAM upgrade I did years ago as a kid on my Atari ST 520. When the install guide for memory talks about scistrors and a craft knife you have to wonder… 🙂

With the new memory modules installed lets check the About menu option:

Easy! Not the Mac Plus is much more usable.

Next steps are networking and connecting up a printer. I would also like to see if I can use it as a termnial, but I am not sure it will compete with my Wyse Terminal with the amber screen…

One of the great things about these old Macs is the screen is rock solid. It is rather like the Atari Mono monitor, both 70Hz and amazing.

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