IBM System/390
The IBM System/390 is the discontinued fifth generation of the System/360 instruction set architecture. The first ESA/390 computer was the Enterprise System/9000 (ES/9000) family, which were introduced in 1990. These were followed by the 9672 CMOS System/390 mainframe family in the mid-1990s. These systems followed the IBM 3090, with over a decade of follow-ons. The ESA/390 was succeeded by the 64-bit z/Architecture in 2000.

History
On February 15, 1988, IBM announced
Enterprise Systems Architecture/370 (ESA/370) for 3090 enhanced ("E") models and for 4381 model groups 91E and 92E.  In additional to the primary and secondary addressing modes that System/370 Extended Architecture (S/370-XA) supports, ESA has an AR mode in which each use of general register 1-15 as a base register uses an associated access register to select an address space. In addition to the normal address spaces that XA supports, ESA also allows data spaces, which contain no executable code.

On September 15, 1990, IBM published a group of hardware and software announcements, two of which included overviews of three announcements:
 System/390 (S/390), as in 360 for 1960s, 370 for 1970s.
 Enterprise System/9000 (ES/9000), as in 360 for 1960s, 370 for 1970s.
 Enterprise Systems Architecture/390 (ESA/390) was IBM's last 31-bit-address/32-bit-data mainframe computing design, copied by Amdahl, Hitachi, and Fujitsu among other competitors. It was the successor of ESA/370 and, in turn, was succeeded by the 64-bit z/Architecture in 2000. Among other things, ESA/390 added fiber optics channels, known as Enterprise Systems Connection (ESCON) channels, to the parallel (Bus and Tag) channels of ESA/370.

Despite the fact that IBM mentioned the 9000 family first in some of the day's announcements, it was clear "by the end of the day" that it was "for System/390," although it was a shortened name, S/390, that was placed on some of the actual "boxes" later shipped.

The ES/9000 include rack-mounted models, free standing air cooled models and water cooled models. The low end models were substantially less expensive than the 3090s previously needed to run MVS/ESA, and could also run VM/ESA and VSE/ESA, which IBM announced at the same time.

IBM periodically added named features to ESA/390 in conjunction with new processors; the ESA/390 Principles of Operation manual identifies them only by name, not by the processors supporting them.

Machines supporting the architecture have been sold under the brand System/390 (S/390) from the beginning of the 1990s.  The 9672 implementations of System/390 were the first high-end IBM mainframe architecture implemented first with CMOS CPU electronics rather than the traditional bipolar logic.

The IBM z13 was the last z Systems server to support running an operating system in ESA/390 architecture mode. However, all 24-bit and 31-bit problem-state application programs originally written to run on the ESA/390 architecture readily run unaffected by this change.

ESA/390 architecture

The architecture (the Linux kernel architecture designation is "s390"; "s390x" designates the 64-bit z/Architecture) employs a channel I/O subsystem in the System/370 Extended Architecture (S/370-XA) tradition, offloading almost all I/O activity to specialized hardware more sophisticated than the S/360 and S/370 I/O channels. It also includes a standard set of CCW opcodes that new equipment is expected to support.

The architecture maintains problem state backward compatibility with the 24-bit-address/32-bit-data System/360 (1964) and subsequent 24/31-bit-address/32-bit-data architectures (System/370, System/370-XA, ESA/370 and ESA/390. However, the I/O subsystem is based on System/370 Extended Architecture (S/370-XA), not on the original S/370 I/O instructions.

ESA/390 is arguably a 32-bit architecture; as with System/360, System/370, 370-XA, and ESA/370, the general-purpose registers are 32 bits long, and the arithmetic instructions support 32-bit arithmetic. Only byte-addressable real memory (Central Storage) and Virtual Storage addressing is limited to 31 bits. (IBM reserved the most significant bit to easily support applications expecting 24-bit addressing, as well as to sidestep a problem with extending two instructions to handle 32-bit unsigned addresses.)

In fact, total system memory is not limited to 31 bits (2 GB). While the virtual storage of a single address space cannot exceed 2 GB, ESA/390 supports multiple concurrent 2 GB address spaces. Further, each address space can have Dataspaces associated with it, each of which can have up to 2 GB of Virtual Storage. While Central Storage is limited to 2 GB additional memory can be configured as expanded storage. With Expanded Storage 4 KB pages can be moved between Central Storage and Expanded Storage. Expanded Storage can be used for ultra-fast paging, for disk caching, and for virtual disks within the VM/CMS operating system. Under Linux/390 this memory cannot be used for disk caching; instead, it is supported by a block device driver, allowing to use it as ultra-fast swap space and for RAM drives.

In addition, a machine may be divided into Logical Partitions (LPARs), each with its own system memory so that multiple operating systems may run concurrently on one machine.

An important capability to form a Parallel Sysplex was added to the architecture in 1994.

Some PC-based IBM-compatible mainframes which provide ESA/390 processors in smaller machines have been released over time, but are only intended for software development.

The Hercules emulator is a portable ESA/390 and z/Architecture machine emulator which supports enough devices to boot many ESA/390 operating systems. Since it is written in pure C, it has been ported to many platforms, including S/390 itself. A commercial emulation product for IBM xSeries with higher execution speed is also available.

Common I/O Device Commands
2.0 Chapter 2. Specific I/O-Device Commands in Enterprise Systems Architecture/390 Common I/O-Device Commands shows the following commands.

S/390 computers
New models were offered on an ongoing basis.

Initial ES/9000 models
Eighteen models were announced September 5, 1990 for the ES/9000, the successor of the IBM 3090. The technology of all but two of the 18 models was similar to the 3090-J, but the models 900 and 820 (codenamed Summit) were greatly enhanced, featuring an on-board split I+D 128+128 KB L1 cache in addition to the 2x2MB L2 cache with 11-cycle latency, more direct interconnects between the processors, multi-level TLBs, branch target buffer and 111 MHz clock frequency. The 900 and 820 were the first models with out-of-order execution since the System/370-195 of 1971. Models 820 and 900 shipped to customers a year later than the models with older technology, in September 1991. Later these new technologies were used in models 520, 640, 660, 740 and 860.

Cooling
Water-cooled ES/9000 models included ES/9021-900, -820, -720, -620, -580, -500, -340 and -330.Air-cooled ES/9000 models included standalone ES/9121-480, -440, -320, -260, -210, -190, and rack mounted: ES/9221-421, -211, -170, -150, -130, -120.

In February 1993 an 8-processor 140MHz model 982 became available, with models 972, 962, 952, 942, 941, 831, 822, 821 and 711 following in March. These models had 30% higher per-processor performance than the 520 to 900 model line. In April 1994 alongside the launch of the first CMOS-based 9672 models, IBM also launched their ultimate bipolar model, the 10-processor model 9X2 rated at 465 MIPS.

Competitive Cooling
By the late 1970s and early 1980s, patented technology allowed Amdahl mainframes of this era to be completely air-cooled, unlike IBM systems that required chilled water and its supporting infrastructure. The 8 largest of the 18 models of the ES/9000 systems introduced in 1990 were water-cooled; the other ten were air-cooled.

ES/9000 features
 ESCON fiber optic channels
 Two of the initially announced models could be configured with as much as 9 Gigabytes of main memory.
 Optional vector facilities were available on 14 of the 18 models, the number of vector processors could be 1, 2, 3, 4 or 6.
 Six models were air-cooled models (and eight water-cooled models); 4 are rack-mounted.

Logical partitioning

Logical Partitions (LPARs) are a standard function on ES/9000 processors whereby IBM's Processor Resource/Systems Manager (PR/SM) hypervisor allows different operating systems to run concurrently in separate logical partitions (LPARs), with a high degree of isolation.

This was introduced as part of IBM's moving towards "lights-out" operation and increased control of multiple system configurations.

Vector facility
The System/390 vector facility was originally introduced with the IBM 3090 system, replacing IBM 3838 array processor (first introduced in 1976 for System/370).

9672 
Introduced in 1994, the six generations of the IBM 9672 machines, "Parallel Enterprise Server", were the first CMOS, microprocessor based systems intended for the high end.  The initial generations were slower than the largest ES/9000 sold in parallel, but the fifth and sixth generations were the largest and most powerful ESA/390 machines built.

In the course of next generations, CPUs added more instructions and increased performance. All 9672s were CMOS, but were slower than the 9021 bipolar machines until the G5 models. The G5 operated at 500MHz, making it at the time (September 1998 to early 1999) the second-highest clocked microprocessor after DEC Alpha. The G5 also added support for the IEEE 754 floating-point formats. In late May 1999 the G6 arrived featuring copper interconnects, raising the frequency to 637MHz, higher than the fastest servers of DEC at the time. CMOS designs permitted much smaller mainframes, such as the Multiprise 3000 introduced in 1999, which was actually based on 9672 G5. The 9672 G3 model and the Multiprise 2000 were the last versions to support pre-XA System/370 mode.

See also
 IBM System/360
 IBM System/370
 IBM 30XX mainframe lines
 IBM 303X
 IBM 308X
 IBM 3090
 IBM Z

Notes

References

External links

 IBM
 IBM Z mainframe homepage
 Current IBM Z mainframe servers
 
 IBM System/390 Photo
 
 
  Multiple links and references.
  Exterior and interior images of the IBM 390.
 

Computing platforms
9000
32-bit computers