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From: jdb@mordor.UUCP (John Bruner)
Newsgroups: net.unix-wizards
Subject: Re: DECtape
Message-ID: <5132@mordor.UUCP>
Date: Mon, 20-Jan-86 15:34:21 EST
Article-I.D.: mordor.5132
Posted: Mon Jan 20 15:34:21 1986
Date-Received: Wed, 22-Jan-86 05:24:53 EST
References: <1464@brl-tgr.ARPA> <14775@onfcanim.UUCP>
Reply-To: jdb@mordor.UUCP (John Bruner)
Organization: S-1 Project, LLNL
Lines: 25

In article <14775@onfcanim.UUCP> dave@onfcanim.UUCP (Dave Martindale) writes:
>You could actually boot from DECtape.  The real challenge was getting a
>minimal root filesytem (bootloader, some inodes, unix, /etc/init, /bin/sh,
>and some of /dev) onto a DECtape.  If I remember correctly, they only
>stored about 256Kb.

When I was looking after an 11/45 I kept a set of standalone utilities
on a (tp-format) DECtape.  When you created a tape with "tp" it would
put "/usr/mdec/tboot" or "/usr/mdec/mboot" (depending upon whether it
was a DECtape or magtape) into block 0.  This single-block bootstrap
knew how to read tp-format files.  This DECtape saved me a lot of
trouble once.  Our root filesystem was located in the center of a
CDC 9766 disc.  Since we had no hardware bootstrap for the SI 9400
controller, we booted the disc by toggling a read command in on the
front panel with the disc write-protected.  Unfortunately, during one
reboot someone neglected to write-protect the disc and toggled in a
64Kb write instead of a read.  We lost the first disc partition but
I was still able to boot using my handy DECtape.

Our magtapes were completely unreliable, so I also did kernel crash
dumps onto DECtape.  An 11/45's 256Kb fits quite comfortably.
-- 
  John Bruner (S-1 Project, Lawrence Livermore National Laboratory)
  MILNET: jdb@mordor [jdb@s1-c.ARPA]	(415) 422-0758
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