Re: Hacker FAQ (please comment and help fix)

Article: 7696 of alt.hackers
Newsgroups: alt.hackers
From: grobson@netcom.com (Gary D. Robson)
Subject: Re: Hacker FAQ (please comment and help fix)
Message-ID: grobsonD7EqnE.95q@netcom.com
Organization: NETCOM On-line Communication Services (408 261-4700 guest)
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Date: Fri, 21 Apr 1995 23:02:01 GMT
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Status: RO

Oops!  Forgot the ObHack in my last posting!  Here it is:

ObHackFromThePast:

When I first started working in the minicomputer world, we were using
7-track tapes.  I was doing an operating system for a 16-bit machine.
The way the system worked was that you'd mount the tape, press the
"reset" switch on the console, and it would read the first sector
of the
boot device (in this case, the tape drive).

This meant that I had to create a driver for the 7-track reel-to-reel
tape drive that fit in a single sector, and that driver needed to load
the bootstrap program from the following sector(s) of the tape.  The
problem was, I could only use opcodes containing zeros in bits 0, 1, 8,
and 9.  It turned out to be possible to make a little routine just a few
instructions long that "decoded" the rest of the sector and
then turned
over control to it.

I spent more time on those cursed 256 instructions than any other single
routine in the OS other than the task switcher.

--
 /---------------------------- Gary Robson ----------------------------\
 |   Internet: grobson@netcom.com | "If it ain't broke, fix it anyway. |
 | CompuServe: 76130,1111         |  How else can you truly learn it?" |
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