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you ever wonder why Amiga computers (from the 80s and 90s) have this weird tic? (
so you can hear it yourself.) turns out there's a really strange reason for it, and it has to do with their floppy drive. 
so you can hear it yourself.) turns out there's a really strange reason for it, and it has to do with their floppy drive.
the noise is annoying, and it's even worse with a second floppy drive! for this one too.
for this one too.
i took apart the Amiga external floppy drive so you can SEE what's going on! it's periodically moving the head from track 0 to track 1 and back with no disk in the drive! 
now why would it be doing that?
now why would it be doing that?
to figure out why, we need to look at one of the earliest Sony 3 1/2" floppy drives from 1983.
the floppy disk drive manual tells us about a special signal called DSKCHG -- this is how the computer can tell that you've removed and replaced the floppy disk. this is important so that the operating system can flush any cached information about the data on the disk.
the Amiga uses this DSKCHG signal to detect when a user has *inserted* a floppy disk into the drive so that it can automatically load the volume information and display an icon on the desktop.
however, DSKCHG is a *latched signal* and must be cleared to be able to tell if a new disk has been inserted. in the diagram 1) DSKCHG is low when the drive's selected w/ no disk--but it's latched. in 2) pulsing the reset line allows DSKCHG to go high since there's a disk.
Sony even gave us a cute little circuit in the manual to clear the DSKCHG signal. so what's the big deal? why didn't the Amiga use the CHGRST line to clear DSKCHG?
later Sony floppy drives did not have the CHGRST line. instead, you had to clear DSKCHG by 1) selecting the drive and 2) pulsing the STEP signal to move the read/write head stepper motor!
some other drives let you step to track -1; doing that cleared the DSKCHG line but the drive logic ignored the step command and the motor remained silent.
the Commodore folks bought disk drives from lots of different companies to keep the costs down. they had no idea if the drive was the kind that supported the -1 seek. they had to assume the worst, so the computer seeks between track 0 and 1, constantly.
still, they left an option in their API to switch over to the silent -1 seek. many Amiga users run software like NoClick to turn on this option. i think the tick is charming, so i leave it be. 
http://aminet.net/package/disk/misc/NoClick
http://aminet.net/package/disk/misc/NoClick
