By Marcel van der Veer
October 2021

Published in category Computing history

More on Algol68C, Fortran, Hercules, MVS, Mainframe, VM

I develop Algol 68 Genie mainly on Debian. To test releases, I keep a "zoo" with operating systems as FreeBSD, OpenBSD and Raspberry Pi OS installed on virtual machines running on top of Debian. Virtualisation began half a century ago as a method of sharing mainframe resources between different operating systems, applications or users.

A well-known example was VM/370 which derived from CP/CMS from the 1960s. The concept was elegant - a mainframe is an expensive resource, so to accomodate different operating systems or many users or servers, the actual machine is virtualised to present itself as many individual machines. Virtualisation works efficiently when a computer emulates itself, and that is what VM/370 did - run many virtual IBM 370's on one physical IBM 370. For timesharing users VM came with the Conversational Monitor System CMS, a small but robust single-user shell. It was the system I worked on when I was a student, and I have fond memories of it. Needless to say that the VM/370 heritage lives on up to the present day in z/VM, as MVS lives on in z/OS.

What is the status of these Jurassic operating systems? The predecessor of MVS, MVT is in the public domain. VM releases through VM/370 Release 6 were open source, and are now also considered to be in the public domain. Since MVS 3.8 was available for order directly from IBM as a no charge product, several Hercules users obtained MVS 3.8J from IBM and made available not only distribution tapes, but even turnkey systems like TK4- for use with Hercules.

For several years I have been using MVS with ALGOL68C on a "hobby mainframe" for use as a reference for Algol 68 Genie. Recently, a VM/370 distribution has been made available that should become a community edition of this vintage system. It actually succeeds in resurrecting VM/370 Release 6, and making CMS usable again by adding for instance a full-screen editor, the FORTRAN H compiler and more.

My main research subject in the 1980's at the University of Nijmegen concerned computational chemistry. Most code I wrote in Nijmegen was in now vintage but back then modern FORTRAN on VM/370 and later VM/SP. For some time I ranked among the heavy users of the university's computer center, which I thought was kind of cool. Hence I did not think very long before deciding to give the VM/370 community edition a whirl. In part I did this of course just for having the satisfaction of being a privileged user - albeit a lonely user - on VM, something unthinkable in the 1980's on the real thing.

On this community edition, I installed as guest operating systems MVS, MVT and VM/370 (VM can run itself and used to be developed this way). For much of this, there are tutorials on the moshix channel. MVS was more or less copied from the VM/370 version generously made available by professor René Ferland. That MVS guest in turn derives from TK4- and is modified to behave well on VM, for instance by spooling job output to the CMS user who scheduled the job.

I reconfigured VM's kernel giving MVS direct access to memory to avoid double paging which is a performance sink when MVS runs on top of VM. Once VM is up, I boot MVS (sorry, ipl MVS) from within a telnet session connected to VM as described below. The VIRTUAL=REAL notification means that double paging is avoided.

$ telnet s370 3270
Connected to s370.
    VM/370 ONLINE
logon mvs ********
LOGON AT 21:30:00 GMT FRIDAY 05/07/21
ipl 148

Once MVS has booted you can DIAL into MVS using a 3270 terminal emulator, and you will be greeted by my personal TSO logon screen:

 MVS/370 Online                                                         
                          VV        VV    MM        MM                    
                          VV        VV    MMM      MMM                    
                   3333333333     777777777777    MM00000000              
                  333333333333    77777777777MM  MM0000000000             
                  33      VV33    77VV    77  MMMM00MM      00            
                           V33     VV    77M   MM 00MM      00            
                            33    VV    77MM      00MM      00            
                         3333VV  VV    77 MM      00MM      00            
                         3333 VVVV     77 MM      00MM      00     _      _    
                            33 VV      77 MM      00MM      00  ." \\`.  (v)   
                            33         77         00        00 ( \\ \\_\_ )\   
                  33        33         77         00        00  \\ _"  //\  )  
                  333333333333         77          0000000000    `/ // /// /
                   3333333333          77           00000000     (//  .__-"    
                                                                   "-" \\      
 Enter logon userid [reconnect]                                         
                                                            RUNNING   VM370CE   

On the MVS guest I installed ALGOL68C. Since the system permits scheduling MVS batch jobs from CMS, I can run ALGOL68C as CMS user in batch mode. Perhaps one day somebody will recover A68C or FLACC for CMS, however for my purposes running batch jobs suffices. I prepare JCL batch files for MVS on CMS, for instance with the full screen editor:

File: CLUSTRUN JCL      A1  RECFM: F LRECL:  72(80) Lines:    62 Current:     9
===== * * * Top of file * * *
===== //CLUSTER JOB (1),MARCEL,CLASS=A,MSGCLASS=A,MSGLEVEL=(1,1),             
===== //        USER=MARCEL,PASSWORD=********
===== //           UNIT=3375,VOL=SER=PUB001
===== //*
===== //*
===== //* ENVIRON
===== //A68ENV   EXEC PGM=A68C,REGION=768K
===== //            SPACE=(CYL,(1,1),RLSE)
===== //            SPACE=(CYL,(1,1,1)),DCB=RECFM=VB,
===== //            UNIT=3375,VOL=SER=PUB001
Unchanged                                                 EE V1.2.5,  1 File(s)
4A                                                                      023/006

Next I submit the JCL file to MVS and fetch the output when the job finishes:

submvs clustrun jcl
Ready; T=0.01/0.01 22:37:05
readcard clustrun listing
Ready; T=0.02/0.06 22:46:15

Next to running ALGOL68C, I use VM/CMS for the preservation of vintage FORTRAN code for computer simulations in chemical physics, and vintage statistical stuff. But that is a story for a future post .

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