Commodore 1581 - Opening a File

NOTE
Besides sequential data files, two other file types are
recorded sequentially on a diskette. They are program files,
and user files. When you save a program on a diskette, it is
saved in order from beginning to end, just like the informa
tion in a sequential data file. The main difference is in the
commands you use to access it. User files can be even more
similar to sequential data files. User files are almost never
used, but like program files, they could be treated as though
they were sequential data files and some can be accessed
with the same commands.
For the advanced user, the similarity of the various file
types offers the possibility of reading a program file into the
computer a byte (character) at a time and rewriting it to the
diskette in a modified form.
OPENING A FILE
One of the most powerful tools in Commodore BASIC is the
OPEN statement. With it, you may send data almost anywhere, much
like a telephone switchboard. As you might expect, a command that
can do this much is fairly complex. You have already used OPEN
statements regularly in some of your diskette commands.
Before you study the format of the OPEN statement, let's review
some of the possible devices in a Commodore computer system:
Device#: Name; Used for;
0 Keyboard Receiving input from the computer operator
1 DATASSETTE™ Sending and receiving information from cassette
2 RS232 Sending and receiving information from a modem
3 Screen Sending output to a video display
4,5 Printer Sending output to a hard copy printer
8,9,10,11 Diskdrive Sending and receiving information from diskette
Because of the flexibility of the OPEN statement, it is possible for
a single program statement to contact any one of these devices, or
even others, depending on the value of a single character in the
command. If the character is kept in a variable, the device can even
change each time that part of the program is used, sending data
alternately and with equal ease to diskette, cassette, printer and screen.
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