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The WELCOME cassette supplied with your BBC Microcomputer has a number of programs stored on it. You can store a copy of any program on cassette and then load it back into the machine at some time in the future. It really is just like recording music onto a cassette - you can then play the cassette back a few days later and the music will still be there.
If you decide that you don't want to keep the computer program that you have saved on cassette then you can just record a new program over the top one in the same way that you can re-use a cassette when recording music. And in the same way that it is very easy to forget where a particular piece of music is recorded on a cassette, so it's very easy to forget where on the cassette you have stored a particular program. It is very strongly suggested that you use the tape counter to keep an index of where programs are on the cassette. Also you must leave gaps between programs. It is very easy to let one program run over the start of the next one if they are all squashed close together. If programs do overlap then you will definitely lose one of them. Be warned!
Most short programs will only move the cassette tape counter on 30 or 40 positions but play safe and spread the programs out over the length of the cassette. If you record the first program at 0000, the second at 0100, the next at 0200 and so on then they will be easy to find and they are unlikely to run over each other.
Note: don't make the mistake of trying to record on the clear plastic tape 'leader' - wind the tape on by hand until the brown tape itself is exposed.
If you have typed a program into your microcomputer then all you have to do to save it is to
SAVE "MYPROG"
on the computer and then press the RETURN key.
If you want to give up at any time then press the ESCAPE key.
Notice that MYPROG is the name that we happened to give to the program. You can call your program by any name you like so long as it has no more than 10 characters. For example you could have typed
SAVE "FRED" or
SAVE "GAME3" or
SAVE "picture"
While the program is being saved on the cassette the name of the program and some numbers will appear to tell you that things are happening. When the computer has finished, the > prompt will re-appear and the tape will stop automatically. If you don't have cassette motor control then you will have to stop the recorder manually after the > prompt re-appears. That's it.
If you want to check that you have successfully recorded your program on the tape then you can use the *CAT command (see page 36). If your recording failed for any reason you can always re-record it. See page 390 if you have problems.
Loading a program back into the computer is just like playing a
particular piece of music which has been recorded on the cassette.
LOAD "MYPROG"
and then press the RETURN key. The message Searching will appear. Of course if your program is called something else then use the right name, for example
LOAD "GAME3"
When the computer finds any program on the cassette it will show the name of the program on the screen. When it finds the program it is looking for it will print "Loading" to let you know that it is now loading the right program.
When the computer has finished loading the program it will print the > prompt. It will also automatically stop the tape if you have automatic motor control, if not then you will have to stop the tape manually.
The program is now in the computer. You can type RUN to make it work, as usual.
There is one more useful feature to do with loading and saving programs. Instead of typing LOAD "MYPROG" you can type CHAIN "MYPROG". This not only loads in the program MYPROG but also starts it working as soon as it has loaded. It saves you having to type RUN after the program has loaded. It is normally more convenient to use CHAIN than LOAD.
If you forget what programs you have on the tape then you can get a catalogue by typing
*CAT
and then playing the tape. But you'll have to wait until the tape has run through the programs.
A typical catalogue looks like this
WELCOME 00 0084
INTRO 08 088E
INDEX 0A 0ABA
KEYBOARD 25 2545
The file-name is followed by two 'hexadecimal' numbers which give the "block number". Each program is recorded as a series of "blocks". See page 71 for an explanation of hexadecimal numbers.
The last number on the line gives the 'length' of the file.
The action of cataloguing a tape also lets the computer verify the information recorded. If there are errors in any of the data on the tape it will print a message and continue.
The ESCAPE key allows you to leave cassette operations whenever you like. If you leave from the middle a LOAD operation you will probably get a Bad Program error. Type NEW to remove this.
More information about cassette formats, loading errors and files is given on page 390.