OS 2200
Unisys stopped producing ClearPath Dorado hardware in the early 2010s, and the operating system is now run under emulation.
However, UNIVAC planned to offer symmetric multiprocessor versions of the 1108 with up to 4 processors and the earlier operating systems (really basic monitor programs) weren't designed for that, even though they supported limited multiprogramming.
William Norris had been one of the founders of ERA and later left Remington Rand to start Control Data Corporation.
In 1986 Burroughs and Sperry corporations merged to become Unisys (which some long time 2200 Series clients say stands for "UNIVAC Is Still Your Supplier").
[3] The major mainframe product lines of both companies have continued in development including the MCP Operating System from Burroughs and OS 2200 from Sperry.
In 2016 Unisys made a virtual Microsoft Windows version of OS2200 available at no cost for educational and leisure purposes.
[5] The specifications for Exec 8 were drawn up by December 1964 as a preliminary Programmers Reference Manual (user guide) and work began in May 1965.
It was designed to run on systems that often had only 128K words (576 K bytes—less than the maximum memory size for the IBM PC XT), and was focused on real time and batch processing.
With severe memory constraints and real time use, keeping only a single copy of code loaded into core was a requirement.
The executive, compilers, utilities, and even sophisticated user applications that might have multiple copies running concurrently were written so that their code could be shared.
In Exec 8, work is organized into jobs, called "runs," which are scheduled based on their priority and need for lockable resources such as Uniservo tape drives or Fastrand drum files.
Input data for an application could be read from a file (generally card images), or immediately follow the @ command in the run stream.
In demand mode, job stream I/O was attached to a terminal handler rather than card image (input) and spool (output) files.
A few years later, more specific time sharing commands were added, and some control statements could be issued asynchronously for immediate processing, even when neither the executive or the running program were expecting data.
CMS 1100 itself ran as a real time multi-threaded program with the privilege of acquiring control of communication lines and submitting transaction messages for scheduling.
Functions that are performed as Services in Windows or Daemons in Linux and UNIX are implemented as either activities within the Exec or as batch programs that are always running in the background.
There are many warnings for writers of transaction programs that they will not be happy with performance if for example they call for a tape mount, but it is permitted.
While they can be used to create or assign files, the most important ones allow a demand user to error terminate a running program or even send it a signal.
Real time is most typically used by long running batch programs, like the OS 2200 communications manager CPComm, but is not restricted to such.
High Exec priority is used by the operator command handler and some other functions that may have to run even when a real time program has control.
This is appropriate for very short-lived transactions such as airline reservations; if one loops due to a programming error, the Exec will terminate it when it reaches its very small configured maximum time.
Customers can also purchase additional performance either temporarily or permanently up to the full capacity of the system if their workload increases or an emergency requires it.
OS 2200 handles applications that use sizes other than multiples of 112 words by indivisibly reading the containing physical records and writing back out the unchanged and changed portions with data chaining.
While contiguous space is allocated if possible, mass storage is treated as a set of pages of 8KB size and a file can be placed in as many areas of the same or different devices as is required.
[20] In OS 2200 each subsystem has its own set of banks that reside in a separate part of the address space that cannot be directly accessed by any user program.
Some subsystems, usually consisting of pure code, such as the run time libraries, may be the direct target of a Call instruction without requiring a gate.
More importantly, the gate controls the specific entry points that are visible, the protection environment in which the subsystem will run, and often a user-specific parameter that provides additional secure information about the caller.
Each console is a terminal window, part of which is reserved for a fixed display that is frequently updated with summary information about activity in the system.
At most they will have Operations Sentinel displays at remote locations monitoring the system and creating alerts when certain events occur.
Most of the historical archives of Unisys are at the Charles Babbage Institute at the University of Minnesota and at the Hagley Museum and Library in Delaware.
