In With The Old…

Some users swear by Aqua interface of MacOS X, others proclaim the desktop-readiness of Linux, the polished presence of Windows XP, or expound upon the stately Solaris as the ultimate operating system. All of these users are wimps.Back in the old days, programmers toggled in boot code on front-panel switches,
submitted jobs through JCL, and counted on a 24 hour operations staff to feed in
the tapes for massive 5Mb datasets of accounting information. Portability
was a pipe-dream, and computer time was far more valuable than that of the lowly programmer.

Many of these operating systems and their descendents are still around. IBM’s phenomenally successful OS/360 is now the 64-bit z/OS, and still provides IBM with billions of dollars in yearly revenue. The market for firms running “modern” versions of PDP-11 operating systems like RSTS, sometimes on original 1970s hardware, is relatively tiny. Nevertheless it still supports several small businesses.

What choices does a retrocomputing hobbyist or OS junky have for taking one of these old OS for a spin? You could choose to troll Ebay for spare parts and dedicate the rest of your budget to expensive air conditioning units and spectacular power bills. But fortunately, thanks to talented and nostalgic programmers, many ancient operating systems will run under emulation via free software packages on Windows, MacOS X, Solaris, and Linux.

We’ll take a quick look at two of the more powerful emulators available, SimH and Hercules.

SimH – The Computer History Simulation Project

SimH,, originally developed by Bob Supnik of DEC, is a spectacular general-purpose emulation package. Focusing on DEC equipment, it also is capable of emulating computers produced by many other manufacturers. Thanks mostly to Mr. Supnik’s many contacts, licenses are available for hobbyists to try out an impressive variety of operating systems.

The following is the list of computers emulated by SimH:

  • Data General Nova, Eclipse

  • Digital Equipment Corporation PDP-1, PDP-4, PDP-7, PDP-8, PDP-9, PDP-10,
    PDP-11, PDP-15, VAX

  • GRI Corporation GRI-909

  • IBM 1401, 1620, 1130, System 3

  • Interdata (Perkin-Elmer) 16b and 32b systems

  • Hewlett-Packard 2116, 2100, 21MX

  • Honeywell H316

  • MITS Altair 8800, with both 8080 and Z80

  • Scientific Data Systems SDS 940

A long list of operating systems distributed in easy-to-use kits is available here:

Most notable among the operating systems SimH allows you to run are the following:

  • Unix V5, V6, and V7 for the PDP-11. Try out the first versions of the Unix operating system on the virtually original hardware.
  • TOPS-10 and TOPS-20, mainframe 36bit operating systems from DEC that lost out internally to…
  • VMS, runnable on an emulated VAX. There are still quite a few jobs out there that call for VMS skills. The hobbyist license program will let you get started on a modern version for $20.
  • CP/M on the Altair 8800. See MS-DOS’ predecessor in action!

SimH runs on Linux, MacOS 9 & X, Solaris, Windows, and many others.

Hercules – System/370, ESA/390, and z/Architecture Emulator

Hercules is an emulator for IBM mainframes. The IBM 360 series dominated computing for years, and even today is an important segment of the market. Hercules will run an enormous variety of operating systems, from the ancient OS/360 to modern-day z/OS and Linux/390 (Linux on the mainframe). The problem is that you can’t actually run modern z/OS without a massively expensive license from IBM.

So other than as way to check out how Linux works on system whose native character set isn’t ASCII, what good is Hercules? Well, all of the old IBM operating systems were not copyrighted. From ancient reel-to-reel tapes have been dredged OS/360, DOS (no, not that DOS), VM/370, MVS, MFT, MVT and others.

Besides Linux/390, the two operating systems available freely for Hercules are most of interest for hobbyists are

  • MVS: A strongly batch-oriented operating system, MVS’ descendants, OS/390 and z/OS, rule the mainframe market. The latest free version of MVS, 3.8J, has been nicely packaged onto a turnkey CD for Linux and Windows. The CD includes compilers for languages like ALGOL, COBOL, PL/I, FORTRAN, and RPG.

    MVS is an extremely robust operating system, and not for the faint of heart. Even by “old school” standards it is spectacularly complicated.

  • VM: Much more user-friendly than MVS, VM survived many periods of official neglect due to its vocal and enthusiastic user-base. VM presents each user with his own virtual machine, complete with its own memory, printer, disk space, and even virtual punchcard reader. Typically a user would run CMS inside his virtual machine, but the key is that he could run *any* mainframe operating system, including VM under itself. There is, of course, a small performance penalty for the overhead. Think VMWARE. The difference is that because unlike x86, the 360-series is completely virtualizable. This means one can run an instance of VM under an instance of VM under an instance of VM under an instance of VM…

    The modern incarnation, z/VM, has gained a new lease on life recently from the popularity of linux on the mainframe. With VM, a mainframe can run hundreds (the record is more than 40,000) of independent copies of the Linux operating system on a single physical machine.

    The most recent freely available version of VM is VM/370. A pre-built system that comes with lots of installed software has been prepared, but it’s quite lacking in documentation. You’ll need to do a bit of reading to figure out how to sign on and start using VM, but it is intrinsically much more user-friendly than MVS

Hercules runs on Linux (including Linux/390 if you happen to have access to a “real” mainframe), Windows, and now MacOS X.

In addition to the Hercules software package itself, you’ll need a 3270 terminal emulator. I suggest QWS3270 for Windows or x3270 for Linux, MacOS X, and other Unix-like operating systems.


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