IBM_System360_Model_30.jpg ibm360m30.jpeg

(left)Wikipedia IBM System/360


"IBM System/360 Model 30 CPU (red, middle of picture), tape drives to its left, and disk drives to its right, at the Computer History Museum."[1]


6 models introduced in 1964

equipped with a set of instructions that can be used for both commercial and scientific calculations(general-purpose computer)

Its name was come from that S/360 can be respond to a wide variety of tasks. "It can respond to 360 degrees (angle of circle), various duties".

several performance and price models: 30, 40, 50, 60, 62, 70, 92, 91, 20, 65, 75, 95, 44, 67, 25, 85, 195, 22 [5]


basis of the mainframe computers around the world

  • Definition of "architecture" by Gene M. Amdahl

    The attributes of a system as seen by the programmer, i.e., the conceptual structure and functional behavior, as distinct from the organization of the data flow and controls, the logical design, and the physical implementation.[3]

  • Computer family

    In the past, the design concept (architecture) was different for each computer, so it was necessary to convert programs and data when migrating from a small machine to a large machine, even for computers of the same manufacturer. In this family, since it is designed with the same architecture from the small machine to the super large-scale machine, it became easy to be upward compatible.

  • refactoring

    Change the inside without changing the behavior seen from the outside

  • modularization

    An approach that combines functional units (modules)

Influential technical features


One or two CPUs

SLT(Solid Logic Technology)

32-bit arithmetic

CISC(Complex Instruction Set Computer)

ISA(Instruction Set Architecture)

a software / hardware interface that unifies the instruction set of a series of products

each machine had each software before the concept of ISA was established

various performance and price models were able to share the same ISA

  • Five types of instruction formats

    RR | Register to Register

    RS |Register to Storage

    RX | Register to Indexed Storage

    SI |Storage Immediate

    SS | Storage to Storage

Instruction Set Architecture


  • Core Memory

    Core memory was the mainstream of computer storage until it was replaced by semiconductor memory chips in the 1950s and early 1970s.

    The core memory consists of small ferrite rings called cores, each of which contains one bit.

    Ferrite_core_memory.jpg memory-cables.jpg


    "A 64 KB core array from the IBM S/360 Model 50. "[7]

  • One Main Memory

    size from 8kB to 8MB depends on each models

  • External Storage

    Low-speed magnetic core memory device Large Core Storage (LCS) were able to connected up to 8MB

8 bits per byte

24-bit addressing

Memory management by memory segmentation and paging

Every address was a physical memory address except for model 67


One to seven channels

Peripheral devices connect to the system via a channel.

I/O processing is slower than CPU, direct control by CPU causes waste resources due to speed difference.

A channel is a dedicated processor with an instruction set optimized for data transfer between peripherals and main memory.

S/360 was designed to handle multiple I/O devices simultaneously.


Wikipedia IBM System/360

  • Other work of channel

    error detection, recovery processing, timeout detection, priority control, load balancing, etc

    Realization of fault tolerance



  • Developed from batch processing with an 80 digit punch card as input
  • Character code adopts EBCDIC
  • The first OS to handle magnetic disk drives (DASD)
  • OS written in System / 360 assembly language


  • Main (large-scale machine)
    - PCP(Primary Control Program) :single task
    - MFT(Multiprogramming with a Fixed number of Tasks):Multitasking for memory for which size and number have been set in advance
    - MVT(Multiprogramming with a Variable number of Tasks) :The size of memory used can be changed dynamically, and the number of tasks to be processed simultaneously can be changed.
  • Sub(small-scale machine): simple systems
    -BOS (Basic Operating System)
    -TOS (Tape Operating System)
    -DOS (Disk Operating System)
  • Fred Brooks

    made influence for software engineering and project management with experience of this project


  • Model 67

    virtualized all hardware interfaces via Virtual Machine Monitor (VMM)

    VMM run directly on the underlying hardware to allow multiple virtual machines (VMs) and then allowed each VM to run its own dedicated operating system instance.

    Conversational Monitor System (CMS)



[1]Wikipedia IBM System/360.

[2]日本アイ・ビー・エム株式会社 北沢強 「System zのテクノロジー変遷」

[3]G.M.Amdahl, G.A.Blaauw, F.PBrooks, "Architecture of the IBM System/360," IBM Journal of R&D, Vol.8, No.2, April, pp.87-101, 1964.

[4]IBM "IBM Archives:Mainframes photo album"

[5]Ken Shirriff’s blog, Iconic consoles of the IBM System/360 mainframes, 55 years old.

[6]International Business Machines Corporation. Student Text Introduction to IBM System/360 Architecture. PDF. International Business Machines Corporation, 1967.

[7]Ken Shirriff’s blog, A look at IBM S/360 core memory: In the 1960s, 128 kilobytes weighed 610 pounds.

[8]The University of Connecticut Prof. Steven A. Demurjian History of Computing – Mainframes.

[9]Wikipedia OS/360 and successors.

[10]M. Tim Jones 仮想 Linux

[11]Wikipedia 磁気コアメモリ

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Last-modified: 2019-07-18 (木) 10:28:44 (919d)