PC-based IBM mainframe-compatible systems

For a period of time PC-based mainframe-compatible systems had a lower price and did not require as much electricity or floor space.

This product used microcode to execute many of the System/370's processor instructions, so that it could run a slightly modified version of IBM's APL mainframe program interpreter.

However, IBM did use their new PC platform to create combinations with additional hardware that could execute S/370 instructions locally.

[4] Besides the 416 kB of usable RAM for S/370 applications, the XT/370 also supported up to 4 MB of virtual memory using the hard drive as its paging device.

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.

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".

[11] 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.

[13] Officially called the IBM 7437 VM/SP Technical Workstation (and later also known as the Personal System/370), it was a freestanding tower that connected to a MCA card installed in a PS/2 Model 60, 70, or 80.

[15] One of its intended roles was to provide a single-user S/370-compatible computer that could run computer-aided design and engineering applications that originated on IBM mainframes such as CADAM and CATIA.

[16] Later, IBM introduced the Personal/370 (aka P/370), a single slot 32-bit MCA card that can be added to a PS/2 or RS/6000 computer to run System/370 OSs (like MUSIC/SP, VM, VSE) parallel to OS/2 (in PS/2) or AIX (in RS/6000) supporting multiple concurrent users.

An additional 370 channel card can be added to provide mainframe-specific I/O such as 3270 local control units, 3400/3480 tape drives or 7171 protocol converters.

Although a single-card product, the P/370 ran three times faster than the 7437, attaining 3.5 MIPS, on par with a low-end IBM 4381.

[23] An important goal in the design of the S/390 Processor Card was complete compatibility with existing mainframe operating systems and software.

The model was revised in mid-1996 and rebranded as the PC Server 520, which featured a 133 MHz Intel Pentium processor.

The S/390 Integrated Server (aka S/390 IS) is a mainframe housed in a comparatively small case (HxWxD are 82 x 52 x 111 cm).

Only 256 MB of ECC Memory and a single CMOS main processor (performance about 8 MIPS) are used; the S/390 CPU used in the Integrated Server is in fact the P/390 E-card.

Fujitsu also continues to make custom S/390-native processors and mainframe hardware for the high end of its BS2000 line.