A user on QL Forum has provided a disassembly of the version 4.00 Argos operating system ROM for Thor machines, which are now quite rare.

Get the disassembly from http://www.dilwyn.me.uk/qlrom/index.html (scroll down the page to “Disassemblies & Sources”).

It’s probably worth noting that images of other versions of the Thor ROM are available to download from the same page.