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Input/Output Control System (IOCS) is any of several packages on early IBM[nb 1] entry-level and mainframe computers that provided low level access to records on peripheral equipment; in some cases[3] IOCS was designed to coexist with SPOOL[4] software.

Types of equipment supported[edit]

IOCS supported several classes of I/O equipment:

  • Disk drives
  • Tape drives
  • Unit record equipment. The record length was dictated by the physical media, which were:
    • Lines of print on paper
    • Punched 80-column[nb 2] cards

Method of access[edit]

IOCS access data through records. 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.

The level of access was at a higher level than that provided by BIOS and BDOS in the PC world; in fact, IOCS had no support for character-oriented I/O.

The implementations and nomenclature of the various IOCS packages vary, but in general a program using IOCS must

  • Identify the IOCS features that it needs. For some IOCS versions this is done via operating system control statements and for others via Macro instructions that expand into the required code.
  • Create control blocks for the individual files. For some IOCS versions this is done through subroutine calls and in others it is done with Macro instructions[nb 3] These control blocks go under different names depending on the particular IOCS and the type of files. Some of the names are
    • Define Disk File (DDF)
    • Define The File (DTF)
    • File Control Block (FCB)
  • Specify the processing. For some IOCS versions this is done through subroutine calls and in others it is done with Macro instructions[nb 3]

Supported systems[edit]

Versions of IOCS existed for the 1401/1440/1460, 1410/7010, 7070/7072/7074[5][6], 7080[7] and 7040/7044/7090/7094[8]. These systems heavily influenced the data management components of the operating systems for the System/360.

External links[edit]


  1. ^ "RCA 3301 Realcom Training Manual", 94-06-000, November 1964
  2. ^ "GE-635 File and Record Control Reference Manual", CPB-1003
  3. ^ "IBM 7070 SPOOL System", J28-6047-1
  4. ^ "SPOOL System", 7070-IO-076
  5. ^ "IBM 7070/7074 Input/Output Control System for IBM 729 Magnetic Tape Units, Unit Record Equipment (7070-IO-904)", C28-6175-3
  6. ^ "IBM 7070/7074 Input/Output Control System for IBM 1301 and 1302 Disk Storage (7070-IO-940)", C28-6272-1
  7. ^ "7080 Input/Output Control System for use with 729 Magnetic Tape Units," Form C28-6237
  8. ^ "Reference Manual, IBM 709/7090 Input/output Control System", C28-6100-2


  1. ^ Other vendors had similar packages, under different names, e.g., File Control Processor (FCP)[1], GEFRC[2].
  2. ^ IBM did not support the 90-column cards used by UNIVAC
  3. ^ a b Which themselves expand into subroutine calls

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