---
title: "ZX81 RAM Extension"
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published_at: "2026-07-12T23:07:36+00:00"
modified_at: "2026-07-12T23:08:01+00:00"
featured_image:
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excerpt: "I am not too sure why anybody would want to use this circuit to extend their RAM when QZX has been offering a free 16 K RAM box for several months now, but the circuit on the following page can be used to add just the amount of RAM that you wish and it is…"
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  - name: "Alex Burr (K5XY)"
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    title: "QZX v10 n8"
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pages: "3-4"
pubdate: "July 1992"
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---

# ZX81 RAM Extension

I am not too sure why anybody would want to use this circuit to extend their RAM when QZX has been offering a free 16 K RAM box for several months now, but the circuit on the following page can be used to add just the amount of RAM that you wish and it is quite easy to build.

This circuit is for a board which will plug into the ZX81’s rear connector, adding up to 4 K of RAM to the existing amount.

- For 1K add IC’s 1,2, and 9.
- For 2 K also add IC’s 3 and 4.
- For 3 K also add IC’s 5 and 6.
- For 4 K also add IC’s 7 and 8.

The 7805 5V regulator should be mounted on a 5 cm (2″) square heat sink.