IBM System/370 Model 135
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 | |
| Manufacturer | International Business Machines Corporation (IBM) |
|---|---|
| Product family | System/370 |
| Released | March 8, 1971 |
| Discontinued | October 16, 1979 |
"Expanded channel capacity
and the ability to use the high-performance
IBM 3330 disk storage under either Operating System (OS)or Disk Operating System (DOS) were ... among the factors significant to the Model 135's ...capabilities."
The IBM System/370 Model 135 was announced March 8, 1971,[1] the only 370 introduced that year. The 135 was IBM's fifth System 370,[a] and it was withdrawn October 16, 1979.
Although microcode was not a uniquely new feature at the time of the 135's introduction, having been used in most System/360 models and in most System/370 models introduced so far, the ability to upgrade a system's microcode without changing hardware, by storing the microcode in read-write memory rather than read-only memory, was not common at that time.[2][3]
The read-write memory containing the firmware was loaded from a "reading device located in the Model 135 console"; this allowed updates and adding features to the Model 135's microcode.[1] The "reading device" was a built-in (read-only) floppy disk drive.[4] The 145, introduced the prior year, also had this feature.[5]
Optional features
The Model 135 was the last of the 370s to be introduced without Virtual memory. Four of the five[b] could be upgraded. Unlike the 155 & 165, which required an expensive[c] hardware upgrade to add a DAT box (Dynamic Address Translation), the 135 & 145 [6] could obtain their virtual memory upgrades from a floppy disk.
Microcode upgrades were also available to add "user-selected options such as
- extended precision arithmetic or
- emulation of the IBM 1400 series."[1][d]
An upgraded Model 135[7] was termed a 370/135-3[e]
Customers of the 370/135 had a choice of four main memory sizes, ranging from 96K to 256K.
Other
- The 370/135 was introduced as running "under either OS or DOS.[1] Newer versions thereof (DOS/VS and OS/VS1) and Virtual Machine Facility/370 (VM/370) subsequently became available options once the 135's microcode was upgraded to support virtual memory. This was priced at $120,000 and came with "increased reloadable control store in addition to some power units." The upgrade could be done "in the field" and the resultant system was now deemed a 370/135-3.[8]
- The 135 was "partly developed at Hursley, UK."[9]