file extension SNX

File extension SNX description:

File extension used by ZX Spectrum emulators for ZX Spectrum programs saved on Microdrive.

Making microdrive copies of your own programs for your own use is not illegal as far as I know, but can be extremely difficult. If you bought a microdrive to speed the loading of your favourite games - the main reason for most people buying them - then it is doubly difficult due to the memory space taken up by the microdrive.
Help, however, is at hand. The Microdriver, from Mirage Microcomputers, is a piece of hardware for the Spectrum which allows you to make a backup copy of any program to microdrive at the push of a button. As the Microdriver has to be connected to the computer to re-load any programs saved using it, it will be of little use to commercial pirates but it is a boon to the home user.
Using the Microdriver is simple. A program is loaded in the normal way, with the Microdriver attached, and at any time - even in mid zap - you can push the button on it and the computer is stopped. A menu appears with a number of options and, once you have made your choice, the program can be started at the same point at which it was stopped.
The menu options are Load and Save; Poke, which allows you to enter those infinitive lives; Run, to restart a program; or New, which clears the computer. All options are error-trapped. If you are saving to microdrive and the program exists, you are given the option of overwriting it. In this way, in an adventure program you can save your current position without having to start at the beginning every time.