Editing IBM System/370 (section)

{{Short description|Family of mainframe computers 1970–1990}}
{{Redirect|IBM 370|the printer|IBM 370 printer}}
{{Infobox CPU architecture
| name        = System/370
| designer    = [[IBM]]
| bits        = [[32-bit computing|32-bit]]
| introduced  = 1970
| design      = CISC
| type        = Register–Register<br />Register–Memory<br />Memory–Memory
| encoding    = Variable (2, 4 or 6 bytes long)
| branching   = [[Status register|Condition code]], indexing, counting
| endianness  = Big
| extensions  = 
| open        = 
| predecessor = [[System/360]]
| successor   = [[S/370-XA]], [[ESA/370]], [[ESA/390]], [[z/Architecture]]
| gpr         = 16× 32-bit
| fpr         = [[IBM hexadecimal floating-point|4× 64-bit]]
| image       = Ordinateurs centraux 348-3-001-2 (edit).jpg
}}

{{IBM mainframes}}

The '''IBM System/370''' ('''S/370''') is a range of [[IBM mainframe]] computers announced as the successors to the [[IBM System/360|System/360]] family on June 30, 1970. The series mostly{{efn|E.g., programs that depended on getting program interrupts for alignment errors might fail.}} 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.

Early 370 systems differed from the 360 largely in their internal circuitry, moving from the [[Solid Logic Technology]] [[hybrid integrated circuit]]s containing separate transistors to more modern monolithic [[integrated circuit]]s containing multiple transistors per integrated circuit, which IBM referred to as Monolithic System Technology, or MST. The higher density packaging allowed several formerly optional features from the 360 line to be included as standard features of the machines, [[floating-point]] support for instance. The 370 also added a small number of new instructions.

At the time of its introduction, the development of [[virtual memory]] systems had become a major theme in the computer market, and the 370 was considered highly controversial as it lacked this feature. This was addressed in 1972 with the System/370 Advanced Function and its associated dynamic address translation (DAT) hardware. All future machines in the lineup received this option, along with several new [[operating system]]s that supported it. Smaller additions were made throughout the lifetime of the line, which led to a profusion of models that were generally referred to by the processor number. One of the last major additions to the line in 1988 were the [[ESA/370]] extensions that allowed a machine to have multiple virtual address spaces and easily switch among them.

The 370 was IBM's primary large mainframe offering from the 1970s through the 1980s. In September 1990, the System/370 line was replaced with the [[IBM System/390|System/390]]. The 390, which was based on a new [[ESA/390]] model, expanded the multiple memory concept to include full [[hardware virtualization]]{{disputed inline|Multiple operating systems|for=It was there earlier|date=April 2024}} that allowed it to run multiple operating systems at the same time.