Pro -
Data General used this algorithm in their RDOS operating system to link
Sequential file blocks. There were three kinds of files: (1) Sequential,
where the directory entry pointed to the first block and the last WORD of
each block was a link word that was the XOR of the previous block address
and the next. (2) Random where the “sequential” linked list of disk blocks
contained the list of data disk blocks. (3) Contiguous - as the name
implies.
RDOS started life around 1972 or so and ran on the company’s Nova series of
16 bit minicomputers. When disks became larger than 32 megs (!!!) they had
to go to a DWORD for the block addresses and links. (At the time the first
disk drives offered by Data General were half a megabyte head-per-track
drives.)
They had a predecessor to RDOS called DOS and it may have used the same
algorithm.
(I thought it was kind of stupid for them to use XOR when their basic
instruction set did not include XOR and a simple arithmetic sum would have
done as well. XOR took 3 instructions to implement.)
Jerry.
>>>>>
Subject: RE: Ptr distance
From: xxxxx@garlic.com (Programmers Society Prokash Sinha)
Date: Wed, 21 Jul 2004 12:42:51 -0700 (PDT)
X-Message-Number: 17
The idea is not definitely new. I first came across couple yrs back in an
article it briefly mentioned, but could not find any implementation, surely
that I did not search exhaustively :-).
If it is in Knuth’s book then it must be an exercise, and surely I would
look
at them soon ( by the wkend) …
Again on tty, so could not include Chuck and Alberto’s msg.
In any case if you guys (anyone ) happen to recall about an implementation
please let me know…
-pro
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