Subject: Re: Reading another disk
Newsgroups: comp.sys.apple2.programmer
From: dempson@actrix.gen.nz (David Empson)
Date: Fri, 24 Dec 1999 22:55:54 +1300
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James <jfjr@bellatlantic.net> wrote:

> What is the command to read another disk, like when the computer asks,
> "Please Enter Side 2 to Continue."

It depends on what operating system you are talking about, and how the
disk has been set up.

With DOS 3.3, this is done by simply displaying the message, waiting for
a keypress (by polling the keyboard in a loop, or using the GET command
in BASIC), then attempting to read the appropriate file.

200 PRINT "Please insert the second disk"
210 PRINT "then press any key";
220 GET A$: PRINT
230 PRINT D$;"RUN PART2"

[or whatever command is appropriate]

With ProDOS, if both disks have the same volume name (like with
AppleWorks Startup and Program, both of which are called "/APPLEWORKS")
then it is generally done in the same way.

If the disks have different names, then the program may attempt to read
a file from the second disk without waiting for a keypress.  If it gets
a "volume not found" error, then it might decide to pause and ask the
user to insert the appropriate disk.  This allows a user with two drives
to avoid the pause.

The problem with this method is that tying the program to the name of
the disk is somewhat restrictive, e.g. it makes it difficult to copy the
program onto a hard drive.

There are more advanced techniques, such as scanning through all online
volumes looking for the desired file, but this is even more risky.

With GS/OS, there is an automatic "please insert disk" dialog, which may
be invoked automatically (I forget now; if not, there will be a special
call to invoke it).  This asks for a volume by its name.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P O Box 27-103, Wellington, New Zealand