IBM System/370 Model 145
| Company type | Computer model |
|---|---|
| Industry | Computer hardware |
| Predecessor | IBM System/370 Model 155 and Model 165 |
| Founded | September 23, 1970 |
| Headquarters | Armonk , United States |
| Products | Mainframe computer |
The IBM System/370 Model 145, introduced on September 23, 1970, was the fourth installment in the IBM System/370 lineup, succeeding the Model 155 and Model 165. This model marked IBM's debut in utilizing semiconductor memory for its main storage, replacing the traditional magnetic core memory. It offered semiconductor memory capacities ranging from 112 KB to 512 KB. This advancement led to a substantial boost in processing speed, making the Model 145 roughly five times faster than the IBM System/360 Model 40. Compatible storage units included devices such as the IBM 3330 and IBM 2319. Shipments were scheduled to begin in late summer 1971, with prices spanning from $705,775 up to $1,783,000.
Virtual memory
At launch, the System/370 Model 145 did not support virtual memory. In contrast to the earlier Models 155 and 165—which demanded expensive hardware additions like a DAT box to enable virtual memory—the Model 145 incorporated associative memory utilized by microcode to maintain DOS compatibility starting June 1971. This hardware feature also allowed virtual memory functionality to be added without significant hardware changes. Although IBM did not officially document or highlight this capability nor annotate the pertinent control registers, customers found that virtual storage could be activated through a microcode upgrade alone, eliminating the need for extra hardware purchases.
This provided two notable benefits over the Models 155 and 165:
- Quicker access to virtual memory (available June 1971 instead of August 1972)
- Virtual memory activation through a microcode update without hardware installation
Operating systems
The 370/145 was compatible with both DOS/360 and OS/360. Initially, it lacked virtual memory support and therefore could not operate virtual memory-based systems. Once virtual memory was enabled via microcode enhancement, the Model 145 became capable of running VMF (Virtual Machine Facility) and VM/CMS, which provided time-sharing capabilities.