roman@sigma.UUCP (Bill Roman) (01/28/86)
I, too, was upset to learn that it might not be possible to protect
my disks against being written on by software run amok, so I tried a
few experiments.
First, I observed that there is no visible LED above or below the
write-protect tab. The location, close to the front of the disk
slot, would seem inappropriate for an optical sensor; it would be
too easily swamped by ambient light.
I tried inserting a disk with the tab in the "protect" position but
with an opaque card over the top of the disk blocking light from
passing through the hole. The Finder (4.1) reported that the disk
was locked.
With the tab still in the "protect" position I covered the hole with
transparent (well, translucent) tape on the bottom side. The Finder
then claimed the disk was unlocked.
I also tried but was unable to reproduce the reported behavior of
Finder 1.1g writing new file names on a locked disk. My conclusion:
the write-protect interlock is mechanical, not optical. Apple's
claim of a hardware protection system would seem to indicate that
our write protected disks really are safe.
I think we would all like the final, official word from Apple on
this matter. In particular, before I spend my money on an upgrade,
are the 800k disks fully protected in hardware?
Larry Rosenstein, are you listening?
--
Bill Roman {ihnp4,decvax,allegra,...}!uw-beaver!tikal!persci!roman
Summation, Inc, (formerly Personal Scientific Corporation)
18702 142nd Ave NE
Woodinville, WA 98072
(206) 486-0991olson@harvard.UUCP (Eric Olson) (01/31/86)
Here's part of the answer to the Write-Lock stuff for Sony drives: I'm sitting here with a naked 400K drive in front of me. What follows is fact (I certainly hope!): - The drive contains two arms, one on each side of the bottom of the disk slot (its easy to see the one on the right through the front of your Mac). - The arm on the right detects disk insertion. If you press it, the Mac will tell you it can't read the (nonexistent) disk. I've used this to reformat disks. - The arm on the left detects write lock. No light shines THROUGH the hole in a write-locked disk, the arm is just allowed to be higher up, "punching through" the hole. Sometimes you get a disk with a faulty write lock tab (tab inserted backwards), and since the tab has an indent on one side (supposed to be the side away from the arm; the top), the disk is always write locked (it is possible to turn the tab over). - The arms (both of them) are NOT connected to microswitches, as one might expect, but to PHOTOINTERRUPTERS (an LED and a photodiode pointing face-to-face with a slot inbetween). So, if it is possible to turn the LED on the left arm off, the disk would think it was write-enabled. I also have a naked 800K drive (which, by the way, is much smaller and has a nifty wafer motor to turn the disk 'round). It has a microswitch on each side, in place of the the arm/interrupter arrangement. So there is no fooling the 800K drives via turning a LED off, but there may be another way. I suspect the remembered experience with Finder 1.1g might just be that it allows you to change things that the new Finders don't (on write-locked disks), but then just didn't update the (write-locked) disk. -Eric.