My PC Thinks It's A Mainframe

Mainframe computers started to appear in the early 1960's as transister technology superseded vacum tube machines. Vacum tube computers could never really get big as the size of a tube combined with the power it used and heat if put out made truly large computers impractical. This was a special time in world history as the Space Race was really heating up. If you were coming of age or a young adult during this period there was a unique sense of unlimited possibilities. As the 60's progressed and turned into the 1970's integration , the ability to etch multiple miniture components on a small silicon wafer, caused an explosion in processing power and a collapse in computing costs. International Business Machines (IBM) quickly dominated the business sector of data processing. They gained the nickname "Big Blue" for the large deep blue metal cabinets that made up their computers. As disk space at this time cost over $100 a megabyte and main storage (RAM) was over $100 kilobyte operating systems had to be direct and to the point. Great effor was put into getting the most thru-put and production from the smallest amount of ram and disk space possible. By 1980 three IBM operating systems had matured from earlier work to become true work horses. All three have evolved into present day offerings of Z/OS, Z/VSE, and Z/VM. For those that worked with this impressive computing equipment from the early days it is amazing that modern PC's can emulate the instruction sets of the old computers and thus run MVS Rel 3.8J from 1980, DOS/VS Rel 34 from 1974, and VM370 Rel6 from 1978 at speeds the old machines could never match. See below the live consoles of the OS's I run for public internet use on several old PC's in my home.

IBM 370 image
Forecast for 2019 Social Security COLA

Live   -   Online Now

myMVS   -   ebay Item
Stand By  -  Connecting to Terminal Server

Stand By  -  Connecting to Terminal Server


MVS Rel 3.8J

The IBM operating system MVS was the most commonly used on the System/370 and System/390 mainframes. It's acronym stands for Multiple Virtual Storage. It was a logical progression from MFT which ran jobs in predefined partition sizes. The version 3.8J is the last version that was made available to the public free of charge and can be run on a PC without license issues. The major restriction of this version is it is limited to 16Mb main memory to be split among all tasks. Later licensed versions of this OS used 31 bit addressing instead of 24 bit. This operating system was designed primarily for batch processing of large amounts of customer billing and account information. It would not be unusual for a small shop to process and print 30,000 customer bills a night every week night. MVS does include TSO (Time Sharing Option) which was an early development in making computers interactive and responsive to transactions as they happen.

myMVS Screen Shots


Test Drive A TSO User Logon

MVS 3.8J and Google Gotcha's
Glossary Common Messages White Papers
Console Commands How To's MVS Control Files
Websites of Interest Vintage MVS Books Assembler Tutorial
Downloads RFE Help File as .txt Forum Messages Group A Group B
Help With Prgram ABEND Codes KICKS For TSO PL1F-and-MVS38j

myVM370   -   ebay Item
Stand By  -  Connecting to Terminal Server
Stand By  -  Connecting to Terminal Server


VM (often: VM/CMS) refers to a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers. The first version, released in 1972, was VM/370, or officially Virtual Machine Facility/370. This was a System/370 reimplementation of earlier CP/CMS operating system. Milestone versions included VM/SP.[1] The current version is z/VM, and is still widely used as one of the main full virtualization solutions for the mainframe market. VM's differences with other IBM mainframe operating systems are primarily due to the unique circumstances in which CP/CMS was built and distributed. [1] The latest public domain version of this OS is release 6 which was made available in 1979.


myVM370 Screen Shots


Test Drive A VM370 User Logon

Glossary Common Messages White Papers
Console Commands How To's VM Control Files
Websites of Interest Vintage VM Books Mainframe Photo Gallery
VM Editor Reference Forum Messages Group A Group B *

myDOSVS   -   ebay Item
Stand By  -  Connecting to Terminal Server

Stand By  -  Connecting to Terminal Server

DOS/VS with POWER Rel 34

DOS/VS Rel 34 is one of the mainframe OS's you can run on your PC. It was introduced in 1974, an upgrade from the first DOS/VS which came out in 1972. The DOS/VS operating system was a continuation of DOS/360 which was a stop gap measure after the introduction of the System/360 computer. IBM had intended for it's customers to migrate to OS/360 when it was released, but many had invested to heavily in DOS/360 to abandon it. So DOS/VS continued as a separate product and eventually developed into DOS/VSE then VSE/SP onto VSE/ESA and finally z/VSE the last release of which was in 2005. The Rel 34 version of the operating system, when run on a modern PC with an emulator, convincingly outperforms the original mainframes that it was developed for. To boot DOS/VS on an 1980's era computer often took more than 15-25 minutes but the Hercules emulator will boot it in less than 1 minute on my old 1.8Ghz spare PC.


myDOSVS Screen Shots


Glossary Search System Messages Downloads
Console Commands How To's DOS-VS Control Files
Websites of Interest Vintage DOS-VS Books Mainframe Photo Gallery
Forum Messages myDOSVS Manual *

A TSO Christmas

Download mvs0080Xmas.txt to put this on your MVS system


The powerful Hercules emulator is what allows us to run a mainframe operating system on a PC. It is open source and runs on Windows, Mac OSX, and Linux machines. It will even run on a Rasberry PI. The offical website is located here. While there are other OS's that can be run with Hercules, the most popular 3 are DOS/VS, MVS, and VM/370. This is a great hobby for retirees that had hands on experience with these operating systems in the 1960's and 1970's.

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Hercules Emulator

DOS/VS with Power Rel 34

MVS Rel 3.8J

Test Drive a TSO Guest Login

Try The Online SUPRTREK Game

VM/370 Rel 6

Test Drive a CMS Guest Login

MTS Rel 6.0A

Test Drive a Student Login


MVT Rel 21.8F


TSS/370 Rel 3


DOS/360 Rel 26.2


Today's Current Mainframes

System/370 Assembler Tutorial

Messages for the hercules-s370asm group

The IBM Compilerator

ALGOL FALGOL 68CAssembler FASSIST Student Assembler
SIMULASNOBOL 4Stony Brook Pascal*

Other OS's for Hercules use

A useful table of
EBCDIC, ASCII, Hex, Decimal, & Octal

IBM Mainframe Glossary

General Computer Glossary

Visit this great collection at:
Other Great Vintage Computer Museums

Using Vintage Mainframe Hardware With Your PC

Videos on vintage IBM and CDC mainframes

IBM Photo Gallery


Some of my other websites


Camping - Hiking Club

TinySpacer - For Amateur Astronomers


The collected computer notes of Calamity Coder

TinySpacer for the fans of old BBS systems


Vintage Digital Equipment Corporation


Website for vintage Control Data Corporation


Vintage Tandy Computers


Amateur Ham Radio in the Digital Age


Not my site but if you are tired of bad news check it out.

IBM 370 image based on work By (Own work)
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