IBM System/370 Model 135

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 The 135 was IBM's fifth System 370,[lower-alpha 1] and it was withdrawn October 16, 1979.

IBM System/370 Model 135
ManufacturerInternational Business Machines Corporation (IBM)
Product familySystem/370
Release dateMarch 8, 1971 (1971-03-08)
DiscontinuedOctober 16, 1979
WebsiteOfficial website IBM Archives
IBM 3330

"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."

Special features

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[lower-alpha 2] could be upgraded. Unlike the 155 & 165, which required an expensive[lower-alpha 3] 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

An upgraded Model 135[7] was termed a 370/135-3[lower-alpha 5]

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]

Images

See also

Notes
  1. of 11
  2. the 135, 145, 155 and 165, but not the 195
  3. $200,000 and $400,000 respectively
  4. (1401, 1440 and 1460)
  5. and the upgrade could be done "in the field."

References
  1. "System/370 Model 135". IBM Archives. IBM. 23 January 2003.
  2. Padegs, A. (September 1981). "System/360 and Beyond". IBM Journal of Research & Development. IBM. 25 (5): 377–390. doi:10.1147/rd.255.0377. In the initial System/360 models, microprograms resided in read-only storage, but in most later models read-write storage is used. - tables include model characteristics (Table 1) and announcement/shipment dates (Table 2). The S/370-155-II and -165-II are listed under the former but not the latter, because the upgraded systems were not formally announced as separate models. The "System/370 Advanced Function" announcement, including the -158 and -168, was the main public event.
  3. "DOS/360: Forty years". Newsgroup: alt.folklore.computers. May 16, 2005. Retrieved 2023-10-02. No, you'll find no IMPL button on a System/360 Model 30. It's control store was Card Capacitive ROS. System/360's used a variety of read only control stores, so changing the microcode meant replacing parts (e.g., with parts that were personalized by punching holes in a card). Later models like the 85 and 25 had writable contol stores, the 85 using a volatile SRAM array and the 25 using a part of core memory.
  4. "Floppy Disks - CHM Revolution". www.computerhistory.org. Retrieved 2021-06-09.
  5. http://www.computerhistory.org/timeline/1968/#169ebbe2ad45559efbc6eb357200edaf describes it as an 80K 8-inch floppy.
  6. IBM Maintenance Library 3145 Processing Unit Theory - Maintenance (PDF) (Fifth ed.). IBM. p. CPU 139. SY24-3581-4.
  7. Computerworld. IDG Enterprise. 1976-07-05.
  8. "Users May Have Jump on Upgrades". Computerworld. July 5, 1976. p. 2.
  9. "Some Key Dates in IBM's Operations in Europe, the Middle East, Asia" (PDF). IBM.
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