====== USG PG-1C300 Issue 3  ======

**Release Date:** March, 1977\\
**Released By:** UNIX Support Group\\
**Source Code: ** [[https://www.tuhs.org/Archive/Distributions/USDL/Cloutier_USG_PG3/usg_pg_issue_3.tar.bz2|usg_pg_issue_3.tar.bz2]] in the [[https://www.tuhs.org/Archive/Distributions/USDL/Cloutier_USG_PG3/|Unix Archive]], browsable in the [[https://www.tuhs.org/cgi-bin/utree.pl?file=USG_PG3|Unix Tree]]\\
**Documentation: ** The [[https://www.tuhs.org/Archive/Documentation/Manuals/Program_Generic_Issue_3/UNIX_Programmers_Manual_Program_Generic_Issue_3.pdf|UNIX Programmer's Manual]]'s for PG-1C300 has been preserved in the [[https://www.tuhs.org/Archive/Documentation/Manuals/Program_Generic_Issue_3/|Unix Archive]]\\
A WIP reconstruction of the manpage sources is maintained [[https://gitlab.com/segaloco/usg_man/-/tree/pg3|here]]

UNIX Program Generic Issue 3, otherwise known as PG-1C300, is a version of the UNIX operating system issued by the UNIX Support Group in March of 1977.  The Program Generic line was used as a standard, supported UNIX base on which to base other projects and supply a computing environment to a larger group of users than the Research group could support.  PG 3 would go on to serve as the base of the real-time MERT Release 0 system.

One particular change is the adoption of a new runlevel-based init system, an ancestor of the inittab-driven systems found in later UNIX branches.  Issue 3 also sees the adoption of SCCS from the PWB project as well as half-duplex terminal support, allowing for the use of various Dataspeed (Teletype) Model 40 terminals.

On April 25th, 2026 it was announced that a copy of Program Generic Issue 3 had been successfully archived, preserved, and resurrected in SimH's PDP-11 emulator.  More can be found [[https://www.tuhs.org/pipermail/tuhs/2026-April/033604.html|here]].

Program Generic Issue 3 includes the following differences from Issue 2:

  * Support for half-duplex terminals such as the Teletype/Dataspeed 40/1 and 40/2 and Tektronix 4010 and 4012 are added via the hd(IV) driver.  More can be found in the document [[https://www.tuhs.org/Archive/Documentation/TechReports/USG_Library/1077_UNIX_DH_11_Driver_to_Support_Both_TTY_and_Dataspeed_40_Terminals.pdf|UNIX DH-11 Driver to Support Both TTY and Dataspeed 40 Timesharing Terminals]]
  * The db(I) and cdb(I) debuggers are retired in favor of adb(I).
  * The PWB/SCCS Release 3 is added.  This version is the prior release described in the PWB/SCCS Release 4.0 PIB [[https://www.tuhs.org/cgi-bin/utree.pl?file=PWB1/usr/news/pibs|here]].
  * as(I) and ld(I) allow specification of the output file name.
  * cat(I) gains the -u (unbuffered) option.
  * cc(I) will pass ".s" files to the assembler.
  * The -E, -D, -I, and -C options are added to cc(I).  In particular, the -C option is used to specify a "compool" directory for include searches.  The default directory is "/compool/".  Additionally an -h option is provided to include the CWD (as opposed to the directory of a source file) in the search path for local includes.
  * cd is added as an alias for chdir(I).
  * Support for the sticky bit is added.
  * The chroot(I) command is added.
  * The cp(I) command gains a -t option to report the number of blocks copied.
  * The cpall(I) and mvall(I) commands are added to bulk-transfer filesystem objects.
  * utmp and wtmp are moved into /etc
  * dd(I) loses the sync conversion flag
  * diff(I) takes on the more familiar e and f options, dropping 1 and 2.
  * diff(I) adds the b option for ignoring whitespace.
  * diff3(I) is added.
  * ed(I) regular expressions add '-' ranges.
  * ed(I) adds subsequent matching of prior subexpressions.
  * ed(I) adds the Q and E commands to override warnings on q and e.
  * ed(I) adds a u command to undo the last s command.
  * Typesetting utilities troff(I), eqn(I), neqn(I), and tbl(VI) are added.
  * ld(I) adds -e and -b options for defining the entry point and memory base respectively.
  * The lines(V)-based init(VIII) is added, resulting in changes to getty(VIII) as well as the retirement of many tty-flavored utilities and pages in favor of line-flavored utilities.  This init system resembles CB/System V init much moreso than Research init.
  * The ps(I) command adds PPID, CPU, NICE, LNE, and TIME for the parent process-id, CPU process magic number, process penalty, line number, and user/system time respectively.
  * The sed(I) command is added.
  * Kill and erase reassignment are added to stty(I).
  * The tail(I) and tee(I) text filters are added.
  * The wall(I) command is added.
  * Character count is added to wc(I).
  * The who(I) command is greatly expanded with regards to the lines(V)-based init and accounting.
  * Errno 14 has been reassigned EFAULT for "Memory fault".
  * Errnos 33-37 have been assigned ETABLE, EFUNC, ENOMSG, ENOALOC, and EBIOCTL.
  * The mdate(II) syscall is dropped.
  * The access, acct, ioctl, ptrace, and tell syscalls are added.
  * The chroot(II) syscall is added, later showing up in 1980's Release 3.0.
  * The call(II) syscall is added as a combined fork-exec.
  * The errlog(II) syscall is added for error logging to an error daemon.
  * The msg(II) IPC primitive is added (more [[https://www.tuhs.org/Archive/Documentation/TechReports/USG_Library/1090_Proposal_for_UNIX_Interprocess_Communication.pdf|here]])
  * The getppid syscall is added to support IPC.
  * The lock(II) semaphore interface is greatly expanded.
  * The signal(II) syscall adds 15 (catchable kill) and 18 (death of a child) signals.
  * TTY 1200 baud support is more clearly stated.
  * The times(II) syscall now returns a struct of longs.
  * The itol(III) and ltoi(III) subroutines are added for packing/unpacking between longs and ints.
  * The lseek(III) subroutine is added for using longs with seeks.
  * The %D, %O, and %X format specifiers for printf(III) are added for specifying decimal, octal, or hexadecimal *long* integers respectively.
  * A %u specifier is added for unsigned integers in printf(III).
  * The cm(IV) minitape interface is added.
  * Line disciplines are supported in the tty(IV) driver via ioctl(II).
  * The dp(IV) Dataphone interface timeout is doubled from 5 to 10 seconds.
  * The suggested hp(IV) disk geometry has changed.
  * The a.out(V) magic number 405 is added as an "overlay" file.
  * A recsize field is added to the header structure of a dump(V).
  * The reform(VI) utility is added.
  * The accton(VIII) utility is added.
  * The dcheck(VIII) and ncheck(VIII) disk utilities are added.
  * The dump(VIII) and restor(VIII) command adds options for 800/1600 bpi switching.
  * The errdemon(VIII) and errpt(VIII) error reporting mechanism is added.
  * The iostat(VIII) I/O statistics utility is added.
  * The load(VIII), mkconf(VIII) and mkpt(VIII) system generation utilities are documented.

See Shamim Sharifuddin Pirzada's [[https://www.tuhs.org/Archive/Documentation/Theses/Shamim_Sharfuddin_Pirzada-1988-PhD-Thesis.pdf|A Statistical Examination of The Evolution of the UNIX System]] for more information about the history of USG UNIX.