ZX Spectrum emulation basics

2019-Jan-18 11:31

is arguably one of the most important personal computers ever. It was released in 1982. and was for its time quite revolutionary.

Considering the power of today's PCs, it's relatively easy to emulate it speed-wise. There are a lot of emulators already written for it, many of them emulating it extremely precisely, including undocumented features.

One of the things that is very convenient is that you can actually play ZX Spectrum games in your browser, implying a JavaScript-based ZX Spectrum emulator.

So what is needed to make a ZX Specturm emulator in JavaScript?


There is a lot of information about ZX Spectrum on the Internet. Here are some that I used:

As usual, Google is your friend.

From emulation standpoint, the main pieces of ZX Spectrum are:

Here are some details that are important from emulation standpoint related to the above hardware list:


ZX Spectrum's 16K ROM was disassembled in great detail, including this HTML version. This was done in 1983.


A lot of ZX Spectrum software, which most likely is a game, is licensed and under copyright. Fortunately, many good authors decided to allow their software to be used freely or licensed as open source. Most importantly:

This is really important when writing an emulator - you actually want to make sure real-world software actually runs on your emulator to confirm it's functioning properly.