The IBM System/370 Model 165 (and the Model 155) were jointly announced June 30, 1970 as "designed for ... the Seventies." That same day IBM announced the 370/195. They were the first three models of the

IBM System/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path ...

line of computers. Three months later a fourth IBM System/370, the Model 145, was announced. Since none of them came with

virtual memory In computing, virtual memory, or virtual storage is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a very ...

, "which was to be a hallmark of the 370 line" some said about these early members of the

family, especially about the 165 & 155, that they were not "the real 370 line."The 195 was noted as "at the time of its introduction, ... IBM's most powerful computing system" and the 145's microcode could be upgraded from a floppy disk. By contrast, the 155 & 165 needed a hardware addition priced at $200,000 and $400,000 respectively

Growth path

The initially announced System/370 Models 165 & 155 systems were in many ways merely improved IBM System/360 systems. * Both were announced to "run under proven OS programming support." (meaning the non-

MFT or MVT

Operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...

s)The Model 155 was also enabled to "run under

DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...

support." * As compared to the 360, their basic architecture was described as "extended, but not redesigned, for System/370. * The

IBM System/360 Model 85 The IBM System/360 Model 85 is a high-end member of the System/360 family of computers, with many advanced features, and was announced in January 1968 and first shipped in December 1969. IBM built only about 30 360/85 systems because of "a reces ...

used microcode to control instruction execution, unlike the completely-

hardwired Hardwire or hardwired may refer to: * Electrical wiring *Hardwired control unit, a part of a computer's central processing unit *In computer programming, a kludge to temporarily or quickly fix a problem *Wired communication In arts and entertainm ...

360/75 and 360/91; the high-end models of

System/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path ...

were also microcoded. Some describe the 360/85 as a bridge to the 370/165.

Upgrade option

In 1972 an upgrade option was announced "to provide the hardware necessary to operate in a virtual memory mode." Unlike the

IBM System/370 Model 145 The IBM System/370 Model 145 was announced September 23, 1970, three months after the 155 and 165 models. It was the fourth member of the IBM System/370 line of computers, and was the first IBM computer to use semiconductor memory for its mai ...

, which as early as June 1971 could have virtual memory capability added to it with a simple microcode update from a floppy disk, the Model 155 and Model 165 needed expensive hardware additions - $200,000 for the 155 and $400,000 for the 165 - to add virtual memory capability, and even this had to wait until 1972. An upgraded 165 was known as an IBM System/370 Model 165-II.

Emulation

The 370/165, when equipped with the appropriate compatibility feature, with the use of an

emulator In computing, an emulator is hardware or software that enables one computer system (called the ''host'') to behave like another computer system (called the ''guest''). An emulator typically enables the host system to run software or use pe ...

program permits running * 7070, 7072 and 7074 programs *

IBM 7080 The IBM 7080 was a variable word length BCD transistor computer in the IBM 700/7000 series commercial architecture line, introduced in August 1961, that provided an upgrade path from the vacuum tube IBM 705 computer. The 7080 weighed about . ...

programs * 709, 7040, 7044, 7094 and 7094 II programs. The 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" and yet "not affect normal operation of System/370."

Physical memory

Although the joint 155/165 announcement did not have the word virtual, there were multiple references to (physical) memory, storage (both main memory and disk storage), and

cache memory In computing, a cache ( ) is a hardware or software component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewher ...

under the name "buffer". The 155 had seven main memory choices, ranging from 256K to 2 MB; the 165: five possibilities, from 512K to 3 MB. Both models were described as having "a very high-performance buffer storage backed by a large" main memory.

Notes

References