MFT (operating system)

In the history of IBM mainframe operating systems, multiprogramming with a fixed number of tasks (MFT) was one of the three available configurations of the OS/360's control program.cite book
author = IBM
title = OS/360 Introduction
series = IBM Systems Reference Library
date = 1972
url = http://bitsavers.vt100.net/pdf/ibm/360/GC28-6534-3_OS360introJan72.pdf
id = GC28-6534-3
pages = 50-51
accessyear = 2007 "there are two configurations of the [OS/360] control program: ... MFT configuration"] In turn, OS/360 was an operating system for the IBM System/360 line of computers.

MFT was intended to serve as a stop-gap until Multiprogramming with a Variable number of Tasks (MVT), the intended "target" configuration of OS/360, became available in 1967. Early versions of MVT had many problems, so simpler MFT continued to be used for many years. After introducing new System/370 machines with virtual memory, the MFT was developed in 1972 into OS/VS1, the last system of this particular line.

The earliest variant of OS/360's control program was the Primary Control Program (PCP). Next, there came two versions of MFT. The first shared much of the code and architecture with PCP, and was limited to four partitions. It was very cumbersome to run multiple partitions. The second version (MFT-II) changed much of the underlying code in the operating system, and was much more flexible to run. The number of partitions increased as well.

Later modifications of MFT-II added "sub-tasking", so that the fixed number of tasks was no longer fixed, although the number of partitions did remain a limitation.

Although officially PCP, MFT and MVT were not a separate operating systems from OS/360, those were only an install-time configuration options—in today's words, a three different variants of OS kernel—because of quite different behaviour and memory requirements, users commonly considered them de facto separate operating systems, and referred to them as "early OS/360", OS/MFT, "OS/MVT", respectively.

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