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Ibm system/370

The meaning of «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[a] maintains backward compatibility with the S/360, allowing an easy migration path for customers; this, plus improved performance, were the dominant themes of the product announcement. In September 1990, the System/370 line was replaced with the System/390.

The original System/370 line was announced on June 30, 1970 with first customer shipment of the Models 155 and 165 planned for February 1971 and April 1971 respectively.[1] The 155 first shipped in January 1971.[2]: 643  System/370 underwent several architectural improvements during its roughly 20-year lifetime.[3][4][5][6][7][8][9]

The following features mentioned in Principles of Operation[3] are either optional on S/360 but standard on S/370, introduced with S/370 or added to S/370 after announcement.

The first System/370 machines, the Model 155 and the Model 165, incorporated only a small number of changes to the System/360 architecture. These changes included:[10]

These models had core memory and did not include support for virtual storage.

All models of the System/370 used IBM's form of monolithic integrated circuits called MST (Monolithic System Technology) making them third generation computers. MST provided System/370 with four to eight times the circuit density and over ten times the reliability when compared to the previous second generation SLT technology of the System/360.[2]: 440 

On September 23, 1970, IBM announced the Model 145, a third model of the System/370, which was the first model to feature semiconductor main memory made from monolithic integrated circuits and was scheduled for delivery in the late summer of 1971. All subsequent S/370 models used such memory.

In 1972, a very significant change was made when support for virtual storage was introduced with IBM's "System/370 Advanced Function" announcement. IBM had initially (and controversially) chosen to exclude virtual storage from the S/370 line.[2]: 479–484 [19] The August 2, 1972 announcement included:

Virtual storage had in fact been delivered on S/370 hardware before this announcement:

Shortly after the August 2, 1972 announcement, DAT box (address relocation hardware) upgrades for the S/370-155 and S/370-165 were quietly announced, but were available only for purchase by customers who already owned a Model 155 or 165.[23] After installation, these models were known as the S/370-155-II and S/370-165-II. IBM wanted customers to upgrade their 155 and 165 systems to the widely sold S/370-158 and -168.[24] These upgrades were surprisingly expensive ($200,000 and $400,000, respectively) and had long ship date lead times after being ordered by a customer; consequently, they were never popular with customers, the majority of whom leased their systems via a third-party leasing company.[23] This led to the original S/370-155 and S/370-165 models being described as "boat anchors". The upgrade, required to run OS/VS1 or OS/VS2, was not cost effective for most customers by the time IBM could actually deliver and install it, so many customers were stuck with these machines running MVT until their lease ended. It was not unusual for this to be another four, five or even six years for the more unfortunate ones, and turned out to be a significant factor[25] in the slow adoption of OS/VS2 MVS, not only by customers in general, but for many internal IBM sites as well.

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