# IBM System/370 Model 135 > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/IBM_System/370_Model_135 > Markdown URL: https://mediated.wiki/source/IBM_System/370_Model_135.md > Source: https://en.wikipedia.org/wiki/IBM_System%2F370_Model_135 > Source revision: 1353268949 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) 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 The 135 was IBM's fifth [System 370](/source/IBM_System/370),[a] and it was withdrawn October 16, 1979. ## Special features Although [microcode](/source/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](/source/IBM_System/370_Model_145), introduced the prior year, also had this feature.[5] ## Optional features The Model 135 was the last of the [370s](/source/IBM_System/370) to be introduced without [Virtual memory](/source/Virtual_memory). Four of the five[b] could be upgraded. Unlike the [155](/source/IBM_System/370_Model_155) & [165](/source/IBM_System/370_Model_165), which required an expensive[c] hardware upgrade to add a [DAT box](/source/Memory_management_unit) (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](/source/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](/source/OS/360) or [DOS](/source/DOS/360).[1] Newer versions thereof (DOS/VS and OS/VS1) and Virtual Machine Facility/370 ([VM/370](/source/VM_(operating_system))) 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](/source/IBM_Hursley), UK."[9] ### Images - [System/370 Model 135 operator's console](https://web.archive.org/web/20060603082249/http://www-03.ibm.com/ibm/history/exhibits/mainframe/images/920912.jpg) - [370/135 with some peripherals](https://web.archive.org/web/20100820214449/http://www-03.ibm.com/ibm/history/exhibits/mainframe/images/p_2423PH3135.jpg) ## See also - [List of IBM products](/source/List_of_IBM_products) - [IBM System/360](/source/IBM_System/360) - [IBM System/370](/source/IBM_System/370) ## Notes 1. of 11 1. the 135, 145, [155](/source/IBM_System/370_Model_155) and [165](/source/IBM_System/370_Model_165), but not the 195 1. $200,000 and $400,000 respectively 1. (1401, 1440 and 1460) 1. and the upgrade could be done "in the field." ## External links - [370 /135 Advertisement: "Presentamos el Sistema/370 Model 135"](http://1.bp.blogspot.com/-EBNFDM7Qzws/URquTsASkXI/AAAAAAAALMc/H5i8X423aBA/s850/sistema)[dead link] ## References 1. ["System/370 Model 135"](https://web.archive.org/web/20050311001920/http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3135.html). *IBM Archives*. IBM. 23 January 2003. Archived from [the original](https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3135.html) on March 11, 2005. 1. Padegs, A. (September 1981). "System/360 and Beyond". *IBM Journal of Research & Development*. **25** (5): 377–390. IBM. [doi:10.1147/rd.255.0377](https://doi.org/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. 1. ["DOS/360: Forty years"](https://groups.google.com/g/alt.folklore.computers/c/RZA6FD27Tc0/m/iHuq1j8860IJ). alt.folklore.computers. May 16, 2005. Retrieved 2023-10-02. No, you'll find no IMPL button on a System/360 Model 30. [*sic*] 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 control stores, the 85 using a volatile SRAM array and the 25 using a part of core memory. 1. ["Floppy Disks - CHM Revolution"](https://www.computerhistory.org/revolution/memory-storage/8/261). *www.computerhistory.org*. Retrieved 2021-06-09. 1. [http://www.computerhistory.org/timeline/1968/#169ebbe2ad45559efbc6eb357200edaf](http://www.computerhistory.org/timeline/1968/#169ebbe2ad45559efbc6eb357200edaf) describes it as an 80K 8-inch floppy. 1. [*IBM Maintenance Library 3145 Processing Unit Theory - Maintenance*](http://www.bitsavers.org/pdf/ibm/370/fe/3145/SY24-3581-4_3145_Processor_Theory_Maintenance.pdf). Fifth ed. IBM. p. CPU 139. SY24-3581-4. 1. [*Computerworld*](https://books.google.com/books?id=pGJK0ayV3S8C&pg=PT1). IDG Enterprise. 1976-07-05. 1. ["Users May Have Jump on Upgrades"](https://books.google.com/books?id=pGJK0ayV3S8C). Computerworld. July 5, 1976. p. 2. 1. ["Some Key Dates in IBM's Operations in Europe, the Middle East, Asia"](https://web.archive.org/web/20050110112224/http://www-03.ibm.com/ibm/history/documents/pdf/emea.pdf). IBM. Archived from [the original](http://www-03.ibm.com/ibm/history/documents/pdf/emea.pdf) on January 10, 2005. --- Adapted from the Wikipedia article [IBM System/370 Model 135](https://en.wikipedia.org/wiki/IBM_System%2F370_Model_135) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/IBM_System%2F370_Model_135?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.