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--- systems:2nd_edition [2023/05/20 17:07] – fix links segaloco
+++ systems:2nd_edition [2023/05/23 08:17] (current) – hardware specifics segaloco
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 **Documentation: ** [[https://www.tuhs.org/Archive/Distributions/Research/Dennis_v2/v2man.pdf|2nd Edition man pages]]
-The second edition of Unix was developed for the PDP-11 at Bell Labs by Ken Thompson, Dennis Ritchie and others. It extended the First Edition with more system calls and more commands. This edition also saw the beginning of the C language, which was used to write some of the commands.
+The Second Edition of Unix was developed for the PDP-11/20 at Bell Labs by Ken Thompson, Dennis Ritchie and others. It extended the First Edition with more system calls and more commands. This edition also saw the beginning of the C language, which was used to write some of the commands.
+The Second Edition, like the first, was only designed to run on the unprotected PDP-11/20 and requires the Extended Arithmetic Element to simulate some operations which would later be supported natively on the PDP-11/45 and other models. This would be the last PDP-11/20 unprotected version of UNIX, as the following Third Edition represents an intermediary PDP-11/45 assembly version of the system and the kernel is rewritten in C before the Fourth Edition.
 The code in the Unix Archive is only the source to some of the commands, some of the library functions, and the C compiler. The files in c/ come from the [[https://www.tuhs.org/Archive/Applications/Early_C_Compilers/last1120c.tar.gz|last1120c.tar.gz]] tape, and form a working C compiler for Second Edition Unix.