BOS/360

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History of IBM mainframe operating systems

IBSYS 1950s CTSS 1961 BOS/360 1965 TOS/360 1965 TSS/360 1967 MUSIC/SP 1960s MTS 1970s

DOS/360 and successors 1966 DOS/VS 1972 DOS/VSE 1980s VSE/ESA 1991 z/VSE 2005

OS/360 and successors 1966 MFT 1966 OS/VS1 1970s MVT 1967 OS/VS2R1 (SVS) 1972 MVS (OS/VS2R2) 1974 MVS/370 1970s MVS/XA 1980s MVS/ESA 1988 OS/390 1995 z/OS 2000

VM line CP-40/CMS 1967 CP-67/CMS 1967 VP/CSS 1968 VM/370 1972 VM/SP 1980 VM/ESA 1988 z/VM 2000

TPF line ACP 1967 TPF 1979 z/TPF 2000s

Unix-like on IBM mainframes UTS 1981 AIX/370 1990 AIX/ESA 1991 Linux 1999

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BOS/360 (Basic Operating System/360) was an early IBM operating system.

It came in 2 versions, 4K BOS and 8K BOS. The latter evolved into DOS/360 which some suggest was really version 6 of BOS. BOS in turn was preceded by BPS, Basic Programming Support. The first 360s to be shipped were the models 30 and 40. BOS was the first disk based operating system^{[citation needed]} and was released in early 1965. 4K BOS was for machines with 8 or 16K of core storage and as its name implies, assembled a Supervisor of about 4K. With very few exceptions, all of the early 360s (but not the model 20) shipped with 2, 3 or more 2311 disk drives.^{[citation needed]} Thus BOS was the only disk based operating system for a machine that was marketed as disk based.^{[citation needed]} The Supervisor was IPL'd and the date and time were entered by the operator on the console typewriter.

The operating system disk contained a source language library, a macro library and a core image library. The macro library included all the options for the supervisor, which was assembled by the 360 assembly language compiler, the only language available at the time, although RPG came a little later. The other crucial component was the Job Controller, which was fed by punched cards using JCL (Job Control Language). Most BOS users upgraded to DOS and added more core, typically to 32K or even a gargantuan (for the time) 64K. DOS was the first System/360 operating system to introduce multi-programming. It could be configured with 2 foreground partitions, typically used for spooling while the main JOB Stream ran in the background.