IBM System/370 Model 165
| Company type | Mainframe computer model |
|---|---|
| Industry | Computer hardware |
| Predecessor | IBM System/360 |
| Founded | June 30, 1970 |
| Successor | IBM System/370 Model 165-II |
| Products | Mainframe computers |
The IBM System/370 Model 165 was unveiled on June 30, 1970, alongside the Model 155, as part of IBM’s newly launched System/370 mainframe series aimed at addressing the computational needs of the 1970s. On that same date, IBM also revealed the high-speed 370/195 model. These three systems represented a significant step forward in IBM's strategy to advance mainframe technology.
Despite their importance, none of these first System/370 machines featured virtual memory, a capability that would later become a hallmark of the 370 family’s competitive advantage. Consequently, early models such as the 165 and 155 were sometimes regarded more as interim solutions than full embodiments of the System/370 architecture.
Three months following their introduction, IBM broadened the System/370 range by launching the Model 145, which incorporated virtual memory technology, thereby strengthening its position in enterprise computing markets.
Virtual memory
The original System/370 Models 165 and 155 lacked support for virtual memory. In 1972, IBM offered an upgrade enabling virtual memory functionality. Unlike the Model 145—which was equipped with virtual memory hardware from its release in June 1971 and received a microcode update in 1972—the Models 155 and 165 required expensive hardware enhancements costing $200,000 for the 155 and $400,000 for the 165 to activate this feature. Once upgraded, the Model 165 was rebranded as the IBM System/370 Model 165-II.
Emulation
With the addition of appropriate compatibility features and emulator software, the 370/165 was capable of executing programs originally designed for earlier IBM machines such as:
- IBM 7070, 7072, and 7074
- IBM 7080
- IBM 7040, 7044, 709, and 7094 (including the 7094 II)
The IBM 7070/7074 Compatibility Feature allowed the Model 165 to run these legacy applications at speeds matching or surpassing those of their original platforms without disrupting standard System/370 operations.
Physical memory
In the joint announcement of the Models 155 and 165, physical memory—including main memory and disk storage—as well as cache memory, were collectively described as "buffer" storage. The Model 155 provided seven main memory configurations ranging from 256K to 2 MB, while the Model 165 offered five options between 512K and 3 MB. Both systems incorporated "very high-performance buffer storage supported by substantial" main memory capacities.
Operating systems
The System/370 Model 165 supported operating systems such as DOS/360 and OS/360. Although compatible with System/370 architecture, both Models 155 and 165 initially lacked virtual memory support, which limited their ability to run operating systems requiring this feature.
IBM supplied complimentary operating systems including DOS/VS, OS/VS1, OS/VS2 Release 1 (SVS), Release 2 (MVS), and Virtual Machine Facility/370 (VM/370) for upgraded Model 165-II machines equipped with virtual memory hardware. Additionally, IBM offered TSS/370 for the Model 165-II as a Program Request for Price Quotation (PRPQ). Various third-party developers also adapted systems like Michigan Terminal System (MTS) and Orvyl from the System/360 Model 67 to run on S/370 machines featuring virtual memory.