The only method for saving and retrieving programs on the MK14 was on to audio cassettes, a slow and unreliable process. It is also difficult to transfer programs between the MK14 and a PC/the Internet. A number of alternative 'loaders' have been developed - the simplest approach is to convert the binary file to a .wav file on the PC and then 'play' that into the MK14 cassette input (I've done this for the Acorn System 1), more reliable but still slow.
Ian Murray (coolsnaz2 on vintage radio forum) has developed a much faster method which loads programs in serial digital format rather than audio - the Fast Loader.
Initially a small Fast Loader program had to be typed into the MK14 (or loaded from cassette) but this has now been integrated into a new version of SCIOS - Version 3. You can check which version of SCIOS you have installed by checking location $0052, if its C5 then you have Version 3 !
There are a number of options for creating the serial data stream, I describe two of them here - Ian's own Web Server based solution which uses an M5StickC Plus and Phil G's (phil__g on vintage radio forum) 'Intel Hex to CS2 Converter and Loader' which runs on an Arduino Nano.