The IBM System/360 Model 25 is a low-end member of the

IBM System/360 The IBM System/360 (S/360) is a family of mainframe computer systems that was announced by IBM on April 7, 1964, and delivered between 1965 and 1978. It was the first family of computers designed to cover both commercial and scientific applica ...

family. It was announced on January 3, 1968, 3 years before the

IBM System/360 Model 22 The IBM System/360 Model 22 was an IBM mainframe IBM mainframes are large computer systems produced by IBM since 1952. During the 1960s and 1970s, IBM dominated the large computer market. Current mainframe computers in IBM's line of business ...

, as a "bridge between its old and new computing systems".

History

At a time when lower priced alternatives, such as

service bureau A service bureau is a company that provides business services for a fee. The term has been extensively used to describe technology-based services to financial services companies, particularly banks. Service bureaus are a significant sector within t ...

s - by 1968, there were 32 such service bureaus serving the US

National Institutes of Health The National Institutes of Health, commonly referred to as NIH (with each letter pronounced individually), is the primary agency of the United States government responsible for biomedical and public health research. It was founded in the late ...

(NIH) alone - and prior generation systems, such as the

Honeywell 200 The Honeywell 200 was a character-oriented two-address commercial computer introduced by Honeywell in December 1963, the basis of later models in Honeywell 200 Series, including 1200, 1250, 2200, 3200, 4200 and others, and the character processor ...

, a competitor to IBM's own

IBM 1401 The IBM 1401 is a variable-wordlength decimal computer that was announced by IBM on October 5, 1959. The first member of the highly successful IBM 1400 series, it was aimed at replacing unit record equipment for processing data stored on pu ...

, were available, this model provided a stop-gap measure. Both the Model 25 and the Model 22, which had been marketed as entry level systems, were withdrawn on the same day, October 7, 1977.

Models

The Model 25 can be configured with 16K, 24K, 32K, or 48K of

core memory Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the central ...

Characteristics

The base Model 25 implements the

System/360 The IBM System/360 (S/360) is a family of mainframe computer systems that was announced by IBM on April 7, 1964, and delivered between 1965 and 1978. It was the first family of computers designed to cover both commercial and scientific applica ...

standard and commercial instruction sets. The scientific or universal instruction sets are optional features. The Model 25 logic is built on

IBM SLT Solid Logic Technology (SLT) was IBM's method for hybrid packaging of electronic circuitry introduced in 1964 with the IBM System/360 series of computers and related machines. IBM chose to design custom hybrid circuits using discrete, flip chip ...

modules mounted on pluggable cards, which are plugged into printed circuit boards. The boards are mounted on hinged metal gates, and are interconnected by flat cables. The Model 25 is the first IBM system to store its

microcode In processor design, microcode (μcode) is a technique that interposes a layer of computer organization between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. Microcode is a laye ...

in a rewritable memory, called the control storage. The control storage uses an additional 16 K (16,384) bytes of core memory. There is also a small part of the core storage that is used to store the contents of registers accessible by software, as well as data used by the microcode. The Model 25 also has a 64-byte high-speed (180 ns) SLT Local Storage, used by the microcode.

Standard Features

*Commercial instruction set *Attachment for

1052 Year 1052 ( MLII) was a leap year starting on Wednesday (link will display the full calendar) of the Julian calendar. Events By place England * Summer – Godwin, Earl of Wessex, sails with a large fleet up the Thames to London, ...

Printer-Keyboard Model 7

Optional Features

*Scientific or universal instruction set *Byte multiplexer channel or selector channel (one of either) *Storage protection *Direct control (with external interrupt) or external interrupt (alone) *Timer (line-frequency type) *

1460 Year 1460 (Roman numerals, MCDLX) was a leap year starting on Tuesday (link will display the full calendar) of the Julian calendar, the 1460th year of the Common Era (CE) and ''Anno Domini'' (AD) designations, the 460th year of the 2nd millennium ...

compatibility *1401/1440/1460 DOS compatibility *

1440 Events January–December * February 21 – The Prussian Confederation is formed. * April 9 – Christopher of Bavaria is elected King of Denmark. * April – Murad II lays siege to Belgrade. The city is heavily damaged, but the defende ...

compatibility * System/360 Model 20 mode *CPU-integrated attachments for: ::One

1403 Year 1403 ( MCDIII) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. Events January–December * January / February – Treaty of Gallipoli: Süleyman Çelebi makes wide-ranging c ...

Prnter Model 2 or 7. After the original announcement the IBM 1403 model N1 was added. ::As many as four 2311 Disk Storage Drives Model 1 (with file scan feature) ::One 2540 Card Read Punch Model 1 (with column binary feature and punch feed read control) ::One 2560 Multi-function Card Machine Model A1 (for Model 20 mode; also for System/360 mode ead/punch onlyif the 2540 emulation feature is added ::CPU-integrated communications attachment ::One 2314 High Speed Channel - this feature is an

RPQ Request price quotation or RPQ is a long-standing IBM designation for a product or component that is potentially available, but that is not on the "standard" price list. Typical RPQ offerings are custom interfaces, hardware modifications, researc ...

, and was not part of the original announcement

Integrated Attachments

The Model 25 has a standard attachment for connection of a 1052 Model 7 console printer-keyboard, which is used as the operator console. Optionally, the Model 25 can have a standard System/360

I/O channel In computing, channel I/O is a high-performance input/output (I/O) architecture that is implemented in various forms on a number of computer architectures, especially on mainframe computers. In the past, channels were generally implemented with cu ...

, that can be either a byte-multiplexor or a selector channel. For the most commonly used peripherals, such as a 2540 or 2560 card reader-punch, a 1403 printer, or 2311 or 2314 disk drives, optional internal attachments are provided. These attachments connect directly to their respective peripherals, and appear to the operating system as if the peripherals were channel-attached. Most unusual about the 360/25 was a feature somewhat analogous to the IBM System/360 Model 44's integrated single disk storage drive, namely an integrated attachment.

Compatibility Features

The Model 25 provides an optional compatibility feature that helps users of

IBM 1400 series The IBM 1400 series were second-generation (transistor) mid-range business decimal computers that IBM marketed in the early 1960s. The computers were offered to replace tabulating machines like the IBM 407. The 1400-series machines stored infor ...

computers migrate to System/360. With the additional Compatibility Feature hardware and Compatibility Support software under DOS/360, the

/1460 object programs can be run in the emulation mode, with little or no reprogramming.

System configuration

The standard set of peripherals is available, although by this time customers had found their way to

IBM-compatible IBM PC compatible computers are similar to the original IBM PC, XT, and AT, all from computer giant IBM, that are able to use the same software and expansion cards. Such computers were referred to as PC clones, IBM clones or IBM PC clones. ...

alternatives. A typical System/360 Model 25 configuration consists of: *IBM 2025 CPU *IBM 1052 console printer-keyboard *IBM 2540 card reader-punch *IBM 1403 printer *One or more IBM 2311 or IBM 2314 disk drives *One or more magnetic tape drives, either IBM 2415 or IBM 2401 model 1, attached to the selector channel

Software

The typical operating system for the Model 25 was

DOS/360 Disk Operating System/360, also DOS/360, or simply DOS, is the discontinued first member of a sequence of operating systems for IBM System/360, System/370 and later mainframes. It was announced by IBM on the last day of 1964, and it was first d ...

, which was loaded from disk. Less common was TOS/360, which was loaded from tape, and, rarely,

BOS/360 Basic Operating System/360 (BOS/360) was an early IBM System/360 operating system. Origin BOS was one of four System/360 Operating System versions developed by the IBM General Products Division (GPD) in Endicott, New York to fill a gap at th ...

, which was loaded from punched cards. Programming was mostly in the

COBOL COBOL (; an acronym for "common business-oriented language") is a compiled English-like computer programming language designed for business use. It is an imperative, procedural and, since 2002, object-oriented language. COBOL is primarily us ...

, RPG and

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languages for the commercial applications that were the predominant uses of this computer, but Fortran IV and could also be used for the scientific and engineering applications, and

PL/I PL/I (Programming Language One, pronounced and sometimes written PL/1) is a procedural, imperative computer programming language developed and published by IBM. It is designed for scientific, engineering, business and system programming. I ...

was available.

Notes

References

External links

Iconic consoles of the IBM System/360 mainframes, 55 years old
{{DEFAULTSORT:IBM System 360 Model 25 System/360 Model 25