Input/Output Control System (IOCS) is any of several packages on early IBM entry-level and mainframe computers that provided low level access to records on peripheral equipment. IOCS provides functionality similar to File Control Processor (FCP) in RCA 3301 Realcom Operating System and GEFRC in GECOS.Computers in the 1950s and 1960s typically dealt with data that were organized into records either by the nature of the media, e.g., lines of print, or by application requirements. IOCS was intended to allow Assembler language programmers to read and write records without having to worry about the details of the various devices or the blocking of logical records into physical records. IOCS provided the I/O support for several compilers.In some cases IOCS was designed to coexist with Simultaneous Peripheral Operations On-line (SPOOL) software. The level of access is at a higher level than that provided by BIOS and BDOS in the PC world; in fact, IOCS has no support for character-oriented I/O. Versions of IOCS existed for the IBM 705 III, 1401/1440/1460, 1410/7010, 7070/7072/7074, 7080 and 7040/7044/7090/7094. These systems heavily influenced the data management components of the operating systems for the System/360; the name IOCS was carried through in DOS/360 through z/VSE, with a distinction between Logical IOCS (LIOCS) and Physical IOCS (PIOCS).Although some technical details and nomenclature are different among the various IOCS packages, the fundamental concepts are the same. For concreteness, the discussion and examples in this article will mostly be in terms of 7070 IOCS. Also, multiple continuation lines will be shown as ellipses (...) when they don't serve to illustrate the narrative.