Bootstrap Idea

John Holden johnh at
Mon Sep 15 09:21:07 AEST 1997

There are a few good tricks to get PDP11 with odd configurations to load. The
first is the venerable paper tape bootstrap. It consists of only 8 instructions
(28 bytes) and works on serial ports. It then loads the 'absolute loader'
which will load formatted data (paper tape!). The format is trival
and has checksums and stop/transfer blocks. The trick is to convert the
unix secordary boot loader from V7 or BSD 2.9-2.11 and then you have
mini loader with lots of device drivers. I can provide some of these
programs including the paper tape listings and images (heck, I still have
a working paper tape reader/punch). You can load ANY PDP-11 this way!

Another approach if you have any of the LSI-11 based cpus with microcoded
console emulator is to use the Xinu suite. It does an initial bootstrap
by sending console commands and then loading a binary boostrap.

On the subject of bad blocks, V6 and V7 offered no bad block strategies.
The DEC spec for RK05's was 200 tracks by 12 sectors by 2 surface plus 3
bad block tracks for 4800 blocks plus 72 spare. The media was generally pretty
good, and all Unix versions used 4872 block filesystems. Files-11 (IAS/RSX) was
the only system to offer bad block replacement (I cannot be sure for RSTS).
When bigger disk drives started showing up, like the RM02/3's and RM05, the
usual practive was to buy packs with 'zero' defects.

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