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From: oster@dewey.soe.berkeley.edu (David Phillip Oster)
Newsgroups: comp.sys.mac
Subject: Re: Is it DANGEROUS to program your Mac...?
Message-ID: <22064@ucbvax.BERKELEY.EDU>
Date: Sat, 5-Dec-87 11:34:29 EST
Article-I.D.: ucbvax.22064
Posted: Sat Dec  5 11:34:29 1987
Date-Received: Thu, 10-Dec-87 06:26:23 EST
References: <870057@hpcilzb.HP.COM>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster)
Organization: School of Education, UC-Berkeley
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In article <870057@hpcilzb.HP.COM> tedj@hpcilzb.HP.COM (Ted Johnson) writes:
>Has anyone seen the article on p22 of the Dec. '87 IEEE "Spectrum"?
>Supposedly it is possible for a buggy program to burn out a flyback
>transformer?!?  The example they give is with an IBM PC..., is this
>a problem with a Mac SE HD20 also?

I've known this since a few months after the IBM was released: The ultimate
copy protection:

"This is an illegal copy. Now erasing copy. Now erasing hard disk. Now
setting fire to your monitor. It is a crime to steal software. Thank you
for your support."

This flaw in the design of IBM video was discovered by some early
screen-savers that darkened the screen by reprogramming the video
controller chip. It was reported in the literature about 1 year after the
IBM PC was released.

The way it works is: An IBM PC CGA or Monchrome video card supports both
80 chars per line and 40 chars per line video modes, and it lets you
adjust the left margin of the picture in software. (This was so the picture
could be shown on your home TV set.) This means there is a lot of software
control over the exact shape of the video waveform. Some waveforms can cause
the high voltage transformer (the flyback transformer) to catch fire on
some monitors.

It takes a while for the transformer to heat hot enough to really damage
itself, so if you are quick, you can keep yourself safe.

A mac, fat mac, macPlus, or SE does not provide as much control over the
waveform, so you should be safe. One exception: I have crashed the machine
so bad that I've lost horizontal synch. (Symptom: a dim screen with a patterns 
of bright, almost horizontal lines (at 25 degree) on the screen. If you see
this, reboot immediately!)

There is all kinds of bizarre stuff in the standard board for the II.
(For example, did you know that Apple's video board for the Mac II supports
smooth scrolling?) So, be careful.

All of this was discussed a few months ago in comp.misc, in a discussion on
exploding computers. (The famed HaltAndCatchFire instruction on some early
IBM mainframes is another good example. This one was supposed to set a block
of memory to zero, but if you only had a partly-populated memory board,
and you tried to clear a lot of it, the amps would send out so much juice that
the core memory caught fire.)

Along the same lines, it is possible to write a set of boot blocks for
the Mac II that appear to boot normally, then power down the machine
before you can actually do anything.

I have a BSR-X10 power control system hooked to my Mac, but I don't let it
control its own power for just that reason.

Though, I really don't worry about damage to my hardware. I worry
about damage to my data. Since I write for a living, my data is much more 
valuable than my hardware.

If you are doing application programming, don't worry about this sort of
thing. My experience has been that you are unlikely to trigger something
disasterous unless you are writing near a danger area.  For example,
there is a SCSI command: EraseHardDisk, but if you access your hard disk
through the File Manager, you are unlikely to write a bug that sends that
command.

--- David Phillip Oster            --A Sun 3/50 makes a poor Macintosh II.
Arpa: oster@dewey.soe.berkeley.edu --A Macintosh II makes a poor Sun 3/60.
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