gus@Shasta.ARPA (01/31/86)
> > > > Then how come my Sony disks work? The write-protect mechanism on those > > diskettes doesn't include a hole going through the diskette - there is a > > small tab that can be moved back and forth, but you can't see through the > > diskette in either mode. > > > > --MKR > No, you don't seem to understand. The tab that you slide back & forth IS > the hole that I'm referring to. (I never said the hole was in the actual > media). When the tab is moved so that you can see through the CASE of the > microdisk, then the disk is locked. > > Robert J. Hammen No! YOU don't undestand! Some early Sony disks don't have a writeprotect hole at all, just as the previous poster described. Unless an LED can differentiate between thick blue plastic and thin blue plastic, the switch MUST be mechanical
gus@Shasta.ARPA (01/31/86)
> > > > > > Then how come my Sony disks work? The write-protect mechanism on those > > > diskettes doesn't include a hole going through the diskette - there is a > > > small tab that can be moved back and forth, but you can't see through the > > > diskette in either mode. > > > > > > --MKR > > No, you don't seem to understand. The tab that you slide back & forth IS > > the hole that I'm referring to. (I never said the hole was in the actual > > media). When the tab is moved so that you can see through the CASE of the > > microdisk, then the disk is locked. > > > > Robert J. Hammen > > No! YOU don't undestand! Some early Sony disks don't have a writeprotect hole > at all, just as the previous poster described. Unless an LED can > differentiate between thick blue plastic and thin blue plastic, the switch > MUST be mechanical > No, I didn't understand. A recent message describes what someone found when closely examining his 400K and 800K drives. I took apart my 400K external drive and found thing to be just as described. Two mechanical sensing levers controlling two photointerrupters with very visible red LED's. I also brought out Larry Kenyon's old disk test program. (The one with all the buttons, switches, scroll bars, etc...) and the hardware chapter of Inside Mac. I started playing around with the "Interface test" window and found things to be just as described in Inside Mac. I was able to eject the disk by manipulating the right control lines which were set up as check boxes. Nowhere in the documentation does it say anything about turning these LEDs on or off or disabling the write protect. Undauted, I noticed, that four control lines provide access to 11 registers documented in Inside Mac. The disk test program seemed to indicate the existence of three more - Eject, a second Sides and a /Exists. None of these were really interesting since they were read-only. What WAS interesting, however, was that there were only FOUR writable registers - DIRTN (Set head step direction), STEP (Step the head), EJECT (Eject the disk) and MOTORON (Turn on/off the disk motor) I also noticed that one of the lines was always 0 (SEL). If there were any extra writable controls, they would probably be accessable by setting SEL to 1, with CA0 and CA1 providing up to four more registers, and CA2 being the data bit to store there. I observed no reaction when experimenting with these four combinations which would indicates that it is NOT possible to defeat the Write Protect in software. Note that my tests were not exhaustive, and I could have missed something. Also, since I didn't write the disk test program, I don't know what internal protections (if any) there might be to avoid a possibly damaging combination of events. I still remain convinced, however, that it is impossible for a fully functioning drive to write to a write protected disk. The proof is in the pudding. The scratch disk that I tested all this on still booted perfectly when I rebooted the machine, even though I was experimenting on track 0, which contains directory and boot information. Now I really feel silly, because we just had Larry Kenyon talk at the SMUG Developers meeting yesterday. If he couldn't resolve this issue one and for all, no one can! Unfortunately, I forgot to ask him! Gustavo Fernandez