IBM System/390

The IBM System/390 was the third 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 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.

IBM System/390 ES/9000
Front cover of the IBM S/390 Parallel Enterprise Server Generation 5
ManufacturerInternational Business Machines Corporation (IBM)
Product family18 initial models,
followed by others
Release dateSeptember 5, 1990 (1990-09-05)
DiscontinuedMay 24, 1998 for the first 18 initial models
Operating systemVSE/ESA, VM/ESA and MVS/ESA
Memoryup to 9 Gigabytes
PredecessorIBM 3090
SuccessorIBM Z
WebsiteOfficial website IBM Archives
"System/390 Announcement". IBM Archives. IBM. Retrieved 2017-01-29.


ESA/390 (Enterprise Systems Architecture/390) was introduced in September 1990[1][2] and 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 Enterprise Systems Architecture/370 (ESA/370) and, in turn, was succeeded by the 64-bit z/Architecture in 2000.

On September 5, 1990 there were three concurrent announcements, using two numbers:

  • 390,[3] as in 360, 370, ... and
  • 9000,[4][5] as in 90, as in 1960 for 360, 1970 for 370, ...
  • Enterprise Systems Architecture/390 (ESA/390): "System/390 introduces the IBM Enterprise System/9000 family"
    was how IBM Marketing introduced ESA.

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,"[4] although it was a shortened name, S/390, that was placed on some of the actual "boxes" later shipped.[6][NB 1]

Among other things, S/390 introduced, under the ESA/390 name:

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.[7] 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

Introduced1990 (1990)
EncodingVariable (2, 4 or 6 bytes long)
BranchingCondition code, indexing, counting
General purpose16
Floating point4 64-bit

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/360 tradition, offloading almost all I/O activity to specialized hardware. It also includes a standard set[2] 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 all intermediate large system 24/31-bit-address/32-bit-data architectures (System/370, System/370-XA, and ESA/370). 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).[NB 2] 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[2] shows the following commands.

ESA/390 I/O-Device Commands
Command Bit Position
0 1 2 3 4 5 6 7
Basic sense 0 0 0 0 0 1 0 0
No-operation (no-op) 0 0 0 0 0 0 1 1
Read configuration data D D D D D D D 0
Read (non-DASD) / Read IPL (DASD) 0 0 0 0 0 0 1 0
Read node identifier D D D D D D D 0
Sense ID 1 1 1 0 0 1 0 0
Set interface identifier D D D D D D D 1
Test I/O (may not be included in a CCW; may only be issued by the associated privileged instruction) 0 0 0 0 0 0 0 0

D Device dependent. The command code, if any, recognized by an I/O device may be obtained by using a sense-ID command.

S/390 computers

New models were offered on an ongoing basis.[8]

Initial ES/9000 models

Eighteen[5] models[NB 3] were announced September 5, 1990 for the ES/9000, the successor of the IBM 3090.


Water-cooled ES/9000 models included ES/9021-900,[9] -820, -720, -620, -580, -500, -340 and -330.
Air-cooled ES/9000 models [10] included standalone ES/9121-480, -440, -320, -260, -210, -190, and rack mounted: ES/9221-421, -211, -170, -150, -130, -120.

ES/9000 water-cooled models[5]
ModelCPUsMax storageMax channelsMax vector fac.
90069 GB2566
82049 GB2564
72064.5 GB1286
62044.5 GB1284
58032.25 GB643
50022.25 GB643
34012.25 GB641
33011152 MB641
ES/9000 air-cooled models[5]
ModelCPUsMax storageMax channelsMax vector fac.
48021024 MB482
44021024 MB482
32011024 MB481
26011024 MB481
21011024 MB481
1901512 MB321
ES/9000 rack-mount models[5]
ModelCPUsMax storageMax channelsMax vector fac.
1701256 MB24-
1501256 MB12-
1301256 MB12-
1201256 MB12-

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.[11]The 8 largest of the 18 models of the ES/9000 systems introduced in 1990 were water-cooled; the other ten were air-cooled.[4]

ES/9000 features

  • ESCON fiber optic channels
  • Two of the 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).[12]


Introduced in 1994, the six generations of the IBM 9672 machines, "Parallel Enterprise Server",[13] 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.[14]

Model[8]Year IntroducedNumber of CPUsPerformance (MIPS)Memory (GB)
G1 – 9672-Rn1, 9672-Enn, 9672-Pnn[15]19941–615–660.125–2
G2 – 9672-Rn2, 9672-Rn319951–1015–1710.125–4
G3 – 9672-Rn419961–1033–3740.5–8
G4 – 9672-Rn519971–1049–4470.5–16
G5 – 9672-nn619981–1088–10691–24
G6 – 9672-nn719991–12178–16445–32

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. 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


  1. S/390 was also used on earlier and subsequent machines.
  2. In the context of computer memory, 1 GB = 10243 bytes
  3. Lower case "M"


  1. Enterprise Systems Architecture/390 Principles of Operation (PDF) (Ninth ed.). IBM. June 2003. p. 1-1. SA22-7201-08. Retrieved December 8, 2018.
  2. Enterprise Systems Architecture/390 Common I/O-Device Commands, Second Edition, IBM, April 1992, SA22-7204-01
  3. "System/390 Announcement". IBM Archives. IBM. Retrieved 2017-01-29.
  4. "ES/9000 Characteristics". IBM Archives. IBM. Retrieved 2017-01-29.
  5. "Enterprise System/9000". IBM Archives. IBM. Retrieved 2017-01-29.
  6. "S/390 Parallel Enterprise Server".
  7. Accommodate functions for the z13 server to be discontinued on future servers
  8. "IBM and Compatible Mainframe Specifications". Technology News of America Co Inc.
  9. "IBM : z/VSE Operating System". IBM. Retrieved 2007-09-17.
  10. Curran, B. W.; Walz, M.H. (1991). "IBM Enterprise System/9000 Type 9121 system controller and memory subsystem design". IBM Journal of Research and Development. IBM. 35 (3): 357.
  11. Giants of Computing: A Compendium of Select, Pivotal Pioneers, by Gerard O’Regan (2013), ISBN 1447153405. "IBM's machines were water-cooled, while Amdahl's were air-cooled"
  12. IBM Corporation. "1976". IBM Archives: 1970s. Retrieved Sep 20, 2018.
  13. "Parallel Enterprise Server". PC Magazine Encyclopedia. Retrieved Sep 19, 2018.
  14. Elliott, Jim (2004-08-17). "The Evolution of IBM Mainframes and VM" (PDF). SHARE Session 9140. Retrieved 2007-10-21. Slide 28: "9672 to zSeries".
  15. "S/390 Parallel Enterprise Server Announcement". IBM. Retrieved 8 July 2011.
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