PC-based IBM mainframe-compatible systems: Difference between revisions

Revision as of 14:46, 5 May 2022

Revision as of 10:03, 22 August 2022

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In October 1983, IBM announced the IBM Personal Computer XT/370. This was essentially a three-in-one product. It could run [[PC DOS]] locally, it could also act as [[3270]] terminal, and finally—its most important distinguishing feature relative to an [[IBM 3270 PC]]—was that it could execute S/370 instructions locally.{{r|byte1984fall}}

[[File:IBM XT370 board (1).jpg|thumb|IBM XT/370 board and diagnostic diskette]]

The XT/370 was an [[IBM Personal Computer XT]] (System Unit 5160) with three custom 8-bit cards. The processor card (370PC-P),<ref>{{cite web |url=https://priorart.ip.com/IPCOM/000059679# |archive-url=https://web.archive.org/web/20151211060121/http://priorart.ip.com/IPCOM/000059679 |url-status=dead |archive-date=2015-12-11 |title=Implementation of IBM System 370 Via Co-Microprocessors/The Co-Processor... - IPCOM000059679D - IP.com |publisher=Priorartdatabase.com |date= |accessdate=2020-07-23 }}</ref> contained two modified [[Motorola_68000_seriesMotorola 68000 series|Motorola 68000]] chips (which could emulate most S/370 fixed-point instructions and non-floating-point instructions), and an [[Intel 8087|Intel 8087 coprocessor ]] modified to emulate the S/370 floating point instructions. The second card (370PC-M), which connected to the first with a unique card back connector contained 512 [[Kibibyte|KiB]] of memory. The third card (PC3277-EM), was a 3270 terminal emulator required to download system software from the host mainframe. The XT/370 computer booted into DOS, then ran the [[VM (operating system)|VM]]/PC Control Program. The card's memory space added additional system memory, so the first {{val|256|ul=KiB}} ([[motherboard]]) memory could be used to move data to the {{val|512 |u=KiB}} expansion card. The expansion memory was dual ported, and provided an additional {{val|384 |u=KiB}} to the XT Machine bringing the total RAM on the XT side to {{val|640 |u=KiB}}. The memory arbitrator could bank switch the second 128 KiB bank on the card to other banks, allowing the XT [[Intel 8088]] processor to address all the RAM on the 370PC-M card.<ref name=Mueller92>Scott Mueller ''Upgrading and Repairing PCs, Second Edition'', Que Books, 1992, {{ISBN|0-88022-856-3}} pages 73-75, page 94</ref> Besides the {{val|416|ul=kB}} of usable RAM for S/370 applications, the XT/370 also supported up to {{val|4 |ul=MB}} of [[virtual memory]] using the hard drive as its paging device.<ref name="killen1984fall">{{cite news | url=https://archive.org/stream/byte-magazine-1984-09/1984_09_BYTE_09-09_Guide_to_the_IBM_PCs#page/n33/mode/2up | title=IBM Forecast / Market Dominance | work=BYTE | date=Fall 1984 | accessdate=18 March 2016 | author=Killen, Michael | pages=30–38}}</ref>

IBM claimed the XT/370 reached 0.1 [[Million instructions per second|MIPS]] (when the data fit in RAM). In 1984, the list price of an XT/370 in its typical configuration was approximately {{US$|long=no|12000}} so compared favorably with IBM's own mainframes on a $/MIPS basis; for example, an [[IBM 4341]] delivered 1.2 MIPS for {{US$|long=no|500000}}. While it theoretically reduced demand on customers' mainframes by offloading load onto the smaller computer, as customers purchased more XT/370s they likely increased the overall load on the mainframes, increasing IBM's mainframe sales.{{r|killen1984fall}}

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Similarly to the mainframe version of [[VM/CMS]], the VM/PC also created the illusion of [[Logical disk|virtual disks]], but on the PC version these were maintained as PC DOS files, either on floppy or hard disk. For example, the CMS virtual disk belonging to user FRED at device address 101 was stored as the DOS file FRED.101. The CMS IMPORT and EXPORT commands allowed extraction of files from these virtual drives as well as [[ASCII]]/[[EBCDIC]] conversion.<ref>BYTE Guide to the IBM PC, fall 1984, pp. 44-46</ref>

The XT/370 came with an XT-style 83-key keyboard (10 function keys).<ref name="byte1984fall">{{cite news | url=https://archive.org/stream/byte-magazine-1984-09/1984_09_BYTE_09-09_Guide_to_the_IBM_PCs#page/n13/mode/2up | title=IBM Personal Computers At a Glance | work=BYTE | date=Fall 1984 | accessdate=18 March 2016 | pages=10–26}}</ref> Newer revisions of the XT/370 dropped the PC3277-EM in favor of the IBM 3278/79 boards. The XT/370 was among the XT systems that could use a second hard drive mounted in the 5161 expansion chassis.<ref name="pc-service-information-manual">{{cite book|title=Personal Computer Family Service Information Manual|date=January 1989|publisher=IBM|id=SA38-0037-00|url=http://bitsavers.org/pdf/ibm/pc/SA38-0037-00_Personal_Computer_Family_Service_Information_Manual_Jul89.pdf}}</ref>{{rp|6-176–17}}

''[[BYTE]]'' in 1984 called the XT/370 "a qualified success". The magazine praised IBM for "fitting all of the 370's features into the XT", and hoped for technical improvements that "might result in an even better computer".<ref name="sabine1984fall">{{cite news | url=https://archive.org/stream/byte-magazine-1984-09/1984_09_BYTE_09-09_Guide_to_the_IBM_PCs#page/n217/mode/2up/search/5160 | title=The IBM XT/370 Personal Computer | work=BYTE | date=Fall 1984 | accessdate=18 March 2016 | author=Sabine, Ernest | pages=210–217}}</ref>

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In 1984, IBM introduced the IBM Personal Computer AT/370<ref>{{cite web|url=https://www-03.ibm.com/ibm/history/documents/pdf/1970-1984.pdf |title=IBM Highlights, 1970-1984 |publisher=IBM}}</ref> with similar cards as for the XT/370 and updated software, supporting both larger hard disks and <!-- 16-bit Dubious, see talk --> DMA transfers from the 3277 card to the AT/370 Processor card. The system was almost 60% faster than the XT/370.<ref name=Mueller92/> The AT/370 used different, 16-bit interface co-processing cards than the XT, called PC/370-P2 and PC/370-M2. The latter card still had only 512&nbsp;KB for memory, out of which 480&nbsp;KB were usable for programs in S/370 mode, while 32&nbsp;KB were reserved for microcode storage. For the terminal emulation function, the AT/370 came with the same 3278/79 Emulation Adapter as the late-series XT/370. The AT/370 motherboard itself was equipped with 512&nbsp;KB of RAM.<ref name="pc-service-information-manual"/>{{rp|9-26 to 9-28}}

The AT/370 also ran VM/PC, but with PC DOS 3.0 instead of 2.10 that the XT version used.<ref>Virtual Machine/Personal Computer User's Guide, p. 1-3, IBM publication number 6137739, December 1984</ref> VM/PC version 2, launched in November 1985, improved performance by up to 50%; it allowed add-on memory (in addition to the disk) to be used as a [[page cache]] for VM.<ref name="Gallant">{{cite journal|author=John Gallant|title=IBM exploiting AT/370 ability|journal=Computerworld : The Newsweekly of Information Systems Management|url=https://books.google.com/books?id=ZUMIDEwANHgC&pg=PA25|date=25 November 1985|publisher=Computerworld|pages=25, 29|issn=0010-4841}}</ref>

A November 1985 ''[[Computerworld]]'' article noted that the machine was "slow selling".<ref name="Gallant"/>

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===S/390 Integrated Server===

[[File:IBM s390 integrated server (1).jpg|thumb|IBM S/390 Integrated Server ]]

The S/390 Integrated Server (aka S/390 IS) is a mainframe housed in a comparably small case (HxWxD are 82 x 52 x 111&nbsp;cm). It became available from November 1998. It is intended for customers who do not require the I/O bandwidth and performance of the [[Multiprise 3000|S/390 Multiprise 3000]] (which has the same size). Only 256 MB of ECC Memory and a single CMOS main processor (performance about 8&nbsp;MIPS) are used; the S/390 CPU used in the Integrated Server is in fact the P/390 E-card. A [[Pentium II]] is used as IOSP (I/O Service Processor). It supports four [[ESCON]] and to four parallel channels. Standard PCI and ISA slots are present. A maximum of 255 GB internal harddisks are supported (16x 18GB HDs, with 2x HDs for redundancy). The supported OSs are OS/390, MVS/ESA, VM/ESA and VSE/ESA.

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Since the late 1990s, PC processors have become fast enough to perform mainframe emulation without the need for a [[coprocessor]] card. There are currently several personal computer emulators available that support System/390 and [[z/Architecture]].