A program like Photoshop might have temporary storage space allocated to it in its preferences. Or virtual memory might eat up hard disk space from the Memory control panel. Or running a big program might take up a lot of memory if the virtual memory not setup or its memory allocation in the Finder Get Info window allows it to eat that much memory. Directory issues could make disk space disappear, for that you might need an old copy of Disk Warrior 2.1.1.
Thanks for offering help so quickly! I've made sure virtual memory is off in Memory control and in the particular programs I use. But you are definitely onto something with the Directory issues. I run Tech Tool 3 relatively frequently for optimization and general "clean up" and that program never has any issues other than a few file date/time inconsistencies. But I recently ran Disk Warrior 2.1 (which has rebuilt the drive with no problems many times before) and got an "original directory is too severely damaged" message (error codes 2156, 2180). It also seems that all these old utility programs are freaking out that we are now in the 2013s - constant pop ups when trying to open them alerting me to a potential "datecannot be right" alert. Perhaps I should change the computer clock and try again? I am just out of ideas!
This. The PRAM battery would cause the time issues ("Your computer is set to a time before 2001.")
Also, it could be to do with temporary files from programs (i.e. not virtual memory).
Finally, if none of this works the HDD may be dying and this is causing the errors (I have seen these symptoms before on a G4/450). Can you hear a clicking noise when you use the computer?
Wow, thanks for all the replies/suggestions guys, I really appreciate it!
a brody: I fear you may be right. I did finally track down an updated copy of Disk Warrior 2.1.1 so I'll see how that works. I've run Tech Tools 3 and even Disk Utility (via Firewire) through my current iMac and they both seem to think the drive is fine. But it is concerning that Disk Warrior used to be able to rebuild the drive...
WZZZ: PRAM battery has never been changed. That's something I should look into. Clock has only "died" once or twice and it hasn't happened recently. I zap the PRAM every now and then when running Tech Tools.
edex67: Hmmm, no clicks. I don't think this is a temporary file issue but I'm going to run some wipe free space utilities. I too fear the HD is just on his way out.
Thanks again, I will let you know if anything happens from all this!
How to upgrade slot loading iMacs
There are two assemblies with the iMac G3. The crt and the computer. The crt is fully enclosed. The computer is a tray that slides off. Working with the computer tray should be safe.
You need to get the 3 and a 1/2 inch ATA harddrive. They are also known as parallel ATA or PATA. The iMac was designed to take a maximum drive size of 128gig. The 120gig drives are the largest readily available. Odd ball sizes do not work like 7gig and 13gig. Pick a size that appeared on the iMac G3 or is a common size greater than 20gig like 40, 60, 80, or 120. Sizes larger than 128 will work but you can access only the first 128gig without buying additional third party software. For very large hd's, format the drive for 127 gig or less.
Check out this site
iMac HDD Upgrade Guide (Slot-Loading) Visual Installation Guide - slot loading iMac Hard Drive <a href="http://wn.com/How_to_Disassemble_an_Apple_iMac_G3" >Visual Installation Guide</a>
You could try to locate the service and repair manual for your iMac on the Internet.
iMac G3 600 is imac_summer01.pdf
other names iMac_slotload_CD.pdf or iMac_early2001.pdf.