IBM System/360 Model 40

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IBM System/360 Model 40
IBM System/360 Model 40 at the USDA
ManufacturerInternational Business Machines Corporation (IBM)
Product familySystem/360
Release dateApril 7, 1964 (1964-04-07)
DiscontinuedOctober 7, 1977 (1977-10-07)
Memory16–128 KB Core

The IBM System/360 Model 40 was a mid-range member of the IBM System/360 family. It was announced on April 7, 1964, shipped in 1965, and withdrawn on October 7, 1977.[1][2]

360/40 with circuit gates open


On April 7, 1964, IBM announced the IBM System/360, to be available in six models.[3][4][5] The 360/40 was first delivered in April 1965.[6]

The 360/30 and the 360/40 were the two largest revenue producing System/360 models,[7] accounting for over half of the units sold.[8]


Five models of the 360/40 were offered.[9] The D40, E40, F40, G40 and H40 were configured with 16K, 32K, 64K, 128K and 256K of core memory and correspondingly 16, 32, 64, 128 and 128 [NB 1] multiplexer subchannels.[9]

The H40 occupied "more floor space than the other models."[9]: p.5 


A typical, early, basic Model 40 system had the following configuration:[10]
Model 40 processor IBM 2040 Central Processing Unit
*128 KB byte storage
*storage protection feature
*universal instruction set
*one multiplexor channel
*two selector channels
*interval timer
Operator console IBM 1052 Typewriter- Keyboard (usually assigned to 009 hexadecimal address)
Unit record device IBM 1442 Card Reader-Punch (00A) or
IBM 2540 Reader-Punch (00C & 00D)
Line printer IBM 1443 Printer (00B) or
IBM 1403 Printer (00E)
Disk storage IBM 2311 Magnetic Disk Drives (190 & 191) or
IBM 2314 Direct Access Storage Facility
Tape storage IBM 2401 Magnetic Tape Units (180 & 181 for 7-track, and 182 & 183 for 9-track)
Telecommunications controller (If used in a telecommunications environment) IBM 2701 Communication Controller


Transformer read-only storage (TROS), from the IBM System 360/40

Like most System/360 models the Model 40 was microprogrammed. The microcode was stored in transformer read-only storage (TROS), organized as up to 8192 words of 56 bits each. Standard microcode consisted of up to 4096 words. The additional 4096 words were used for the 1401 or 1410 compatibility feature.[11]

IBM 1400 series emulation[edit]

With the additional Compatibility Feature hardware and Compatibility Support software under DOS/360, the IBM 1401/1440/1460 object programs could be run in the emulation mode, with little or no reprogramming.[12]


Although the cover of IBM's MVT Guide[13] indicates that even a 360/40 could run MVT, the IBM operating system used was usually the realistically sized DOS/360,[citation needed] because all but one model of the 360/40 had less than MVT's minimum memory requirements of 256KB.[14][15]

The IBM System/360 Model 40 was developed at IBM Hursley[16] and manufactured at IBM's facilities in: Poughkeepsie, U.S., Mainz, Germany; and Fujisawa, Japan.[17]

A modified Model 40 ran CP-40, the ancestor of CP/CMS, which in turn was the progenitor of the VM line.


  1. ^ not a typo: the physical limit seemed to be 224; see p. 17 of the Model 30 Functional Characteristics


  1. ^ IBM System/360 Model 40 (IBM Archives)
  2. ^ IBM System/360 model 40 (Flickr from Yahoo!)
  3. ^ Emerson W. Pugh (1995). Building IBM: Shaping an Industry and Its Technology. Cambridge, Massachusetts: MIT Press. p. 275. ISBN 0-262-16147-8.
  4. ^ Martin Campbell-Kelly; Daniel D. Garcia-Swartz (2015). From Mainframes to Smartphones. Harvard University Press. ISBN 9780674729063.
  5. ^ Fortune magazine, Sept. 1966, p.118
  6. ^ "System/360 Dates and characteristics". IBM. 23 January 2003.
  7. ^ Pugh, Emerson W.; Johnson, Lyle R.; Palmer, John H. (1991). IBM's 360 and early 370 systems. Cambridge, Massachusetts: MIT Press. ISBN 9780262161237.
  8. ^ An ADP Newsletter cited on page 56 in Weiss, Eric A., ed. (1969). Computer Usage Essentials. McGraw-Hill. LCCN 71-76142. shows sales of the 360 Model 30 (36%) and the Model 40 (22.6%), for a total of 58.6%
  9. ^ a b c IBM System/360 Model 40 Functional Characteristics (PDF). August 1971. A22-6881-2.
  10. ^ IBM System/360 Model 40 Operating Techniques (PDF). IBM. C20-1635-2.
  11. ^ IBM Corporation (1970). IBM Field Engineering Manual of Instruction: System/360 model 40 Functional Units (PDF). pp. 52–73.
  12. ^ IBM System/360 Disk Operating System 1401/1440/1460 Emulator Programs: Compatibility Support/30 & /40 (PDF) (Third ed.). IBM. February 1969. C27-6940-2.
  13. ^ IBM System/360 Operating System: MVT Guide OS Release 21.7 (PDF). IBM. August 1974. GC28-6720-5.
  14. ^ IBM System/360 Operating System: Storage Estimates OS Release 21.7 (PDF). IBM. April 1973. GC28-6551-16.
  15. ^ Ray Saunders. "MVS... And Before OS/360 ?". Archived from the original on 2007-12-20.
  16. ^ Nicholas Enticknap. "Editorial". Resurrection: The Bulletin of the Computer Conservation Society (23). Mike Flinders, who also worked at Hursley where the 360/40 was designed
  17. ^ "Fujisawa plant". IBM Archives. 23 January 2003.