"Expanded channel capacity and the ability to use the high-performance IBM 3330 disk storage under either Operating System (OS)orDisk 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 The 135 was IBM's fifth System 370,[a] and it was withdrawn October 16, 1979.
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[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
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]
^Padegs, A. (September 1981). "System/360 and Beyond". IBM Journal of Research & Development. 25 (5). IBM: 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.
^"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 [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.
