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

Revision as of 21:37, 20 January 2006

Revision as of 21:54, 20 January 2006

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Since the rise of the [[personal computer]] in the 1980s, [[IBM]] and other vendors have created '''PC-based IBM-compatible mainframes''' which are compatible with the larger IBM [[mainframes]]. They are also referred to as ''plug-compatible mainframes'', a term used for the original System/360 and 370 compatible clones. The original advantage being that the PC-based mainfarmes had a much smaller footprint, required less power, and cost less money.

The '''S/390 Integrated Server''' (short for System/390 Integrated Server) was a low-end [[IBM]] [[mainframe]] offering in the mid-1990s. Unlike other [[ESA/390]] mainframes, the S/390 Integrated Server was actually an S/390 processor card installed in an IBM PC Server or [[RS/6000]]. Another unusual feature in the mainframe world was its use of internal [[Direct access storage device|DASD]], although external storage was also available. It came in two varieties, the [[POWER]]-based R/390 and the [[Pentium]]-based P/390.

==Background==

==S/390 Processor Card==

Up until the late 1980s, mainframes were very large machines that often occupied entire rooms. The rooms were often air conditioned and had special power arrangements to accomodate [[three-phase power]] required by the machines.

==System/370==

* Details about the System/370 based PC mainframes from the 1980s.

==System/390==

===S/390 Processor Card===

An important goal in the design of the S/390 Processor Card was complete compatibility with existing mainframe operating systems and software. The processor implements all of the ESA/390 and XA instructions which prevents the need for instruction translation. The S/390 Processor Card also incorporated 32MB of dedicated memory with an optional 96MB daughter card for a combined total of 128MB of RAM. The processor was officially rated at 4.5 [[Million instructions per second|MIPS]].

===R/390===

R/390 was the designation used for the expansion card used in an IBM RS/6000 server. The R/390 featured a 67 MHz or 77 MHz [[POWER]] 2 processor and 32MB to 512MB of RAM, depending on the configuration. R/390 servers required AIX to be run as the host operating system.

===P/390===

P/390 was the designation used for the expansion card used in an IBM PC Server and was less expensive than the R/390. The original P/390 server was housed in an IBM PC Server 500 and featured a 90 MHz [[Intel]] [[Pentium]] processor for running OS/2. The model was revised in mid-1996 and rebranded as the PC Server 520, which featured a 133 MHz Intel Pentium processor. Both models came standard with 32MB of [[RAM]] and were expandable to 256MB. The PC Server 500 featured eight [[Micro Channel architecture|Micro Channel]] expansion slots while the PC Server 520 added two [[Peripheral Component Interconnect|PCI]] expansion slots and removed two Micro Channel slots.

===S/390 Integrated Server===

==Uses==

* Details on the S/390 Integrated Server.

The S/390 Integrated Server was not a particularly powerful mainframe, even when it was released. It was commonly used for development and as a cheaper replacement of older mainframes. It was capable of running [[OS/390]] as well as older 24-bit operating systems, but due to its inherent 31-bit design, cannot run current versions of [[z/OS]].

==z/Architecture and Today==

Since the late 1990s, PC processors have become fast enough to perform mainframe emulation without the need for a peripheral card. One of the most popular PC-based IBM-compatible mainframe products as of 2006 is Fundamental Software's [[FLEX-ES]] product. FLEX-ES emulates both System/390 (ESA/390) and z/Architecture. While FLEX-ES is capable of running on most PC hardware, the licensing agreement prohibits it. FLEX-ES must run on approved IBM xSeries servers or ThinkPad laptops.

Another popular emulator is the open source [[Hercules emulator]], which has been in development since 1999 and emulates the System/370, System/390, and z/Architecture instruction sets. While Hercules cannot legally run modern IBM operating systems, earlier System/370 operating systems are considered to be public ___domain and can be legally run on Hercules.

==External links==