I have around 500 floppy disk images from an Apple II and IIgs BBS/usergroup that closed down recently. Some of the disks are bootable, but many aren't. Is there an easy way to tell if a disk boots into something useful without loading up an emulator?

These disks are a mix of DOS 3.3, ProDOS 8, IIgs ProDOS 16 and Pascal formats.

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    At least for DOS 3.3, IIRC every disk was "bootable", even if only to print a message saying NO OPERATING SYSTEM or something. – Greg Hewgill Oct 8 '17 at 23:55
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    You can read the boot sector to determine which type of OS it is, or if it just has the "NO OS" bootsector, but that won't tell you into what application it will eventually bootstrap. And the boot process is complicated, most OS can execute some kind of "turnkey" program after the OS is booted. As long as this is done the standard way, I guess one could write some sort of script to find out, but there always will be the odd disk that does something different ... – dirkt Oct 9 '17 at 9:12
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    You could probably use the "Internet Archive Python library 1.0.9" from archive.org to parse the disks. I think they get screen shots by trying to boot with mame. – PeterI Oct 9 '17 at 10:36
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    @PeterI - I've already put all the disks on archive.org, but IA will only start an emulator if you give it emulator_ext:dsk and emulator:apple2ee as additional metadata – scruss Oct 9 '17 at 17:30
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    Looks like they now have screenshots on archive.org – PeterI Oct 10 '17 at 9:16

The bootprocess itself don't know any 'not bootable' exit. If a disk can be read, the first sector is loaded at 800 and then jumped to 801 (800 holds a counter for the number of sectors to read by the bootloader - usually 1). If there is no sector to be found, it spins indefinit.

Non bootable disks may have some kind of error message, but don't have to. You could try to scan for certain loader signatures as found in common OS. But thats a rather fruitless task.

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    Maybe perform a disassembly and check for any attempts to access the drive hardware? I'm dense as to the Disk ][ but either hitting certain addresses or calling certain ROM routines. That's the sort approach I take in emulation all the time — it tends to hit 99.99% of cases as there is little benefit to bring obscure in your boot sector. – Tommy Oct 9 '17 at 0:44
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    Looks like I might as well assume they're all bootable, and have Internet Archive see if they're not. – scruss Oct 9 '17 at 17:31
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    When crashing and hanging count as bootstrapping (-: – hippietrail Jul 1 at 1:16

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