IBM System/370 Model 168

The IBM System/370 Model 168 (and the Model 158)[1])were both announced August 2, 1972[2]

IBM System/370 Model 168
ManufacturerInternational Business Machines Corporation (IBM)
Product familySystem/370
Release dateAugust 2, 1972 (1972-08-02)
DiscontinuedSeptember 15, 1980
Memoryup to eight megabytes of integrated monolithic processor storage
WebsiteOfficial website IBM Archives

Prior 370 systems had not "offered virtual storage capability, which was to be a hallmark of the 370 line," and some said that the 168 and 158 were the first "real 370" products.[3]

By contrast, "in 1972, the System/370 Advanced Function was released and had new Address Relocation Hardware and now supported four new operating systems (VM/370, DOS/VS, OS/VS1, OS/VS2)."[4]

The 158 and 168 were withdrawn Sep 15, 1980.


Main memory

Main memory for the Model 168, which was "four-way doubleword interleaved," could be 1 to 8 megabytes, with offerings selectable in increments of one megabyte.[5]

Newer technology than that of the 370/165, which had been introduced 2 years prior, used "monolithic, instead of magnetic core" memory,[5] resulting in a system which was faster and physically smaller than a Model 165.[5]:pp.3–5

System console

The newly introduced IBM 3066 Model 2 System console

  • included a light pen[NB 1]
  • replaced "most switch, pushbutton, and indicator functions"[NB 2][5]:p.32
  • as with the 165's Model 1, had a microfiche document viewer,[NB 3] a feature introduced for the 360/85's console.[NB 4]

A console printer (up to 85 characters per second) to provide hard copy was optional when the console was in display mode, and required when it was in printer-keyboard mode.

Disk storage

The newly introduced Model 11 of IBM's 3330 family of disk drives, featuring removable disk packs, has double the capacity of the prior 100-megabyte offerings.[NB 5][NB 6] It can't be attached to a 370/165.[5]:p.94


Both the 370/168 and the 370/158 had MP (multiprocessing) models that offered "tightly coupled multiprocessing.[1]

The 168 was described[2] as having "two types of multiprocessing support" since it also offered attaching a second processing unit, an IBM 3062 Attached Processing Unit, which lacked access to Input/Output channels.

Extended precision floating-point

This feature adds support for 128-bit "hexadecimal" floating-point operands. It is standard on all 165 and 168 models, and is an "Optional (no-charge)" feature on the 370/158.[5]:p.137


The optional IBM 7070/7074 Compatibility Feature allowed the 165 to "run 7070 and 7074 programs at speeds that, in general, equal or exceed those of the original systems"[6] and yet "not affect normal operation of System/370."[5]:p.139[6]:p.5

Other listed options are:

  • 7080 Compatibility
  • 709/7090/7094 II Compatibility

There is a limitation, however, described as:
"Note: Compatibility features are mutually exclusive."

168-1 & 168-3

The Third (June 1975) edition of IBM's 168 Guide introduced the 168-3.
"There are two versions of the Model 168: the Model 1 and the Model 3."[5]:preface

IBM referred to the System/370 Model 168-3 as "the company's ... flagship."[NB 7]

The 168-3 CPU's internal performance has been described as 5 - 13% faster than the 168-1.[5]:p.125

See also


  1. Although only the 158 announcement mentioned the light pen, the 168's manual says "light pen is standard."
  2. among the few retained: "system clear" and "cooling reset alarm"
  3. the online manual has an extra dot: "d.ocument"
  4. the 360/85 article includes a photo of same
  5. It has the same number of platters but double the number of data cylinders.
  6. Similar to the Massbus / DEC RP05/RP06 100 MB/200 MB capacities and number of cylinders.
  7., when comparing it and the then-new IBM 3033.


  1. "System/370 Model 158". IBM Archives. IBM.
  2. "System/370 Model 168". IBM Archives. IBM.
  3. "What Course for the 3081?". Computerworld. November 24, 1980. p. 34.
  4. Marshall, David; Reynolds, Wade A.; McCrory, Dave. Advanced Server Virtualization. p. 8. ISBN 1420013165.
  5. "A Guide to the IBM System/370 Model 168" (PDF). IBM. June 1975.
  6. "7070/7074 Compatibility Feature for IBM System/370 Models 165, 165 II, and 168" (PDF). IBM. June 1973. GA22-6958-1.
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