Adventures in Macintosh restoration Part V: Good laser, bad laser
Where to start?
Since this is going to be a “crossover” machine, the most important thing for me to test is the floppy drive. But at this point, the only way I can get into a running system is via a Floppy Emu device and an image of the Mac OS 8.1 Disk Tools floppy (see Part III). Unfortunately, with the Floppy Emu taking up the floppy connection, I can’t test the floppy drive at the same time.
If I had or could make a real floppy of the 8.1 Disk Tools I could use that and try to boot the system, but I didn’t. Time to check out the CD-ROM.
Burning a Mac OS 8.1 CD
I didn’t (and still don’t) have the original system CD I ordered. However I found plenty of Toast images of Mac OS install CDs online, and through my research discovered that they’re just standard ISO images. Which means I should be able to burn them on my PC. Not wanting to mess with too many variables I downloaded an image for Mac OS 8.1, dug up a blank CD-R, and burned it.
I popped the finished disc into the mac, started it up, and… nothing. It tried to spin up, but didn’t boot. I assumed I messed something up – maybe you can’t create bootable CDs this way, or maybe the slower 12X CD-ROM was having trouble reading a CD-R burned at 52X. Despite storing digital data, the CD burning process is actually analog, and burning a CD too fast can make discs that older readers can’t read.
Next I tried booting from the Floppy Emu again, and putting in the CD anyway, just to see if I could see any files on it. It tried to spin up , but again, no dice. Maybe the CD-R was just bad – it had been sandwiched in a spindle of old PC games. I still had a couple more blanks, so I tried burning a new disc at the slowest speed my burner would handle, 32X.
Popped the second CD into the mac, and again, nothing. I flipped the disc over to check for scratches – then I noticed something peculiar. The Mac OS 8.1 CD image was only ~200MB, only a third of a full CD, yet the CD looked blank.
I won’t get into the details of optical media here, but basically, on professionally pressed CDs, the data is physically etched into the disc as a series of pits and bumps. Recordable CDs instead have a thin layer of transparent, heat-sensitive dye in them, and a CD burner writes data by heating up the dye until it becomes opaque, creating a series of transparent and opaque dots, rather than pits and bumps.
A side effect of this is that it’s easy to see if a disc has data on it just by looking at the bottom of the disc, and seeing the color of the opaque dye. Since data is written in a continuous spiral from the center to the outer edges of the disc, you can even estimate how full it is by seeing where the color stops.
Broken CD burner
The bottom of the two discs I burned showed no sign of having any data on it, especially not the third I expected. To confirm I put the discs back in my PC, where every program I tried saw them as fresh blank discs. I tried to burn on them again, and even though each program declared success, I noticed the read buffer (where data is stored before it’s burned) was always at 0%.
Turns out my CD burner (actually a modern DVD-burner, on my desktop from 2018) can’t burn anymore. While many modern computers (especially laptops) dispense with an optical drive all together, and I don’t burn often these days, I did burn a lot of CDs on this drive a couple years ago. Plus I regularly use the drive for ripping optical media, which I had noticed was giving me problems lately. Bottom line, it’s broken, and I can’t use it to burn CDs.
Thankfully, I still had an old external USB DVD burner from ~2009 that I could try. I plugged it in and tried to burn the image again. Success! It even supported burning as slow as 10X, safely under the speed of the 12X reader in this mac.
Third time’s a charm
Time to try again. I popped in the burned CD (with the definite color change on the bottom), held “C” on the keyboard to ensure it booted from the CD drive, and it worked! The Mac OS 8.1 install CD booted perfectly fine, right into a desktop with the installer ready to run.
Even better, once it booted I was able to browse the CD and I found it contained a copy of the “Disk Tools” floppy image I had used previously, along with the software to write it to a real floppy. A couple clicks later, I was able to confirm the floppy drive works too, and I created my first mac floppy in almost twenty years.
Now, they both probably could use some maintenance, but I’ll save that for another day. I was two for two with working drives – I could read and write floppies, essential for communicating with older machines, but I wasn’t limited to floppies for getting data onto the system – I could transfer large files with burned CDs.
That’s it for this post – the machine works, the drives work, next is to get a hard drive installed – but that’ll wait until Part VI.
Want to read from the beginning? Start at Part I.