The "PR#n"
command in
Applesoft and
Integer Basic redirects output to slot n. The result of typing the command depends entirely on what card, if any, you have installed in that
slot.
The general convention with Apple II slots was:
- Slot 0: 16K RAM upgrade for Apple II/II+. PR#0 and IN#0 generally negated the effects of PR#n and IN#n.
- Slot 1: Printer interface
- Slot 2: Modem or serial interface connected to external modem
- Slot 3: 80 column card. Yes, 80 columns was an option on the Apple II series.
- Slot 4: Usually a mouse interface
- Slot 5: 3.5" Disk controller, for 800K 3.5" floppies.
- Slot 6: 5.25" Disk controller, for 140K 5.25" floppies
- Slot 7: AppleTalk interface. This was rare, but was present on some Apple II's hooked up to Macintosh networks.
There is also a
sister command, "IN#n", which redirects input to the specified slot. For instance, if someone was
dialed up to you with a
modem, and your modem is in slot 2, typing the following at the BASIC prompt:
PR#2
IN#2
would allow the
remote person to "use" your computer. Neat, huh?
Strange things would happen (unpredictable results, the manuals always said) if you tried to PR#n or IN#n a slot with nothing in it. Sometimes this would cause the machine to get hosed in a fun and humorous way. This is because if there is no card installed the peripheral card ROM space for that slot was unpredictable. You could be executing random code. Best to remove any disks from your drives before doing this.