IBM System/370 Model 135
| Company type | Mainframe computer model |
|---|---|
| Industry | Computer hardware |
| Predecessor | IBM System/360 Model 135 |
| Founded | March 8, 1971 |
| Defunct | October 16, 1979 |
| Successor | IBM System/370 Model 145 |
| Products | Mainframe computer |
The IBM System/370 Model 135, unveiled on March 8, 1971, was the sole System/370 model released that year and marked IBM's fifth installment in the System/370 lineup. Its production ceased on October 16, 1979.
Special features
Although microcode implementation was typical in earlier System/360 and System/370 machines, the Model 135 distinguished itself by allowing microcode updates without hardware modifications. This was achieved by storing microcode in writable memory instead of fixed read-only memory, providing enhanced flexibility for updates and additional functionalities.
Firmware loading was facilitated through a built-in reading mechanism within the Model 135's console—a dedicated read-only floppy disk drive. This feature, also found in its predecessor, the System/370 Model 145, supported streamlined microcode management and system improvements.
Optional features
Among the 370 series, the Model 135 was the final model introduced lacking Virtual memory. Out of five models (135, 145, 155, 165, excluding the 195), four were capable of being upgraded. Unlike the 155 and 165 models, which necessitated expensive hardware enhancements (costing $200,000 and $400,000 respectively) to incorporate a DAT box (Dynamic Address Translation), both the 135 and 145 could receive virtual memory upgrades via floppy disk installation.
Microcode revisions also permitted customers to add optional features such as
- extended precision arithmetic capabilities
- emulation support for the IBM 1400 series (including models 1401, 1440, and 1460).
Once upgraded, the Model 135 was identified as the 370/135-3, with these enhancements performed on-site.
Clients had the option to select from four primary memory configurations ranging between 96K and 256K.
Other
- Initially, the 370/135 operated under either OS or DOS. Subsequent releases (DOS/VS, OS/VS1) as well as Virtual Machine Facility/370 (VM/370) became supported following microcode upgrades that enabled virtual memory. This enhancement required an investment of $120,000 and included expanded reloadable control storage along with additional power units. The upgrade process could be conducted "in the field," resulting in the updated 370/135-3 model.
- The development of the 135 involved contributions from IBM’s facility at Hursley, United Kingdom.
