IBM System/390

IBM System/390
Company type	Mainframe computer series
Industry	Computer hardware
Predecessor	ESA/370 architecture
Founded	1990
Successor	z/Architecture
Products	Mainframe computers implementing ESA/390 architecture
Parent	IBM

IBM System/390

The IBM System/390 represents a now-obsolete series of mainframe computers that implemented the ESA/390 architecture, which is the fifth evolution of the System/360 instruction set. The initial ESA/390 models were introduced as the Enterprise System/9000 (ES/9000) lineup in 1990. Subsequently, IBM launched the 9672, Multiprise, and Integrated Server families from 1994 through 1999, all utilizing CMOS microprocessor technology. ESA/390 succeeded the ESA/370 architecture, which powered Enhanced IBM 3090 and 4381 "E" models, as well as the System/370 architecture found in entry-level IBM 9370 mainframes. In 2000, ESA/390 was replaced by the 64-bit z/Architecture.

History

On September 5, 1990, IBM revealed several significant hardware and software offerings, highlighting three primary systems:

System/390 (S/390), extending the naming lineage from earlier decades of IBM mainframes.
Enterprise System/9000 (ES/9000), a versatile family comprising rack-mounted units alongside air- and water-cooled configurations. These cost-effective systems took over from predecessors like the 3090 and 4381 to support operating systems such as MVS/ESA, VM/ESA, and VSE/ESA.
Enterprise Systems Architecture/390 (ESA/390), marking IBM’s final iteration of a 31-bit mainframe design, which was also adopted by competitors including Amdahl, Hitachi, and Fujitsu. ESA/390 followed ESA/370 and paved the way for the advent of the 64-bit z/Architecture in 2000. A notable innovation within ESA/390 was the introduction of fiber optic Enterprise Systems Connection (ESCON) channels alongside traditional Bus and Tag channels.

While IBM initially emphasized the ES/9000 series during its announcements, the System/390 brand ultimately became the dominant identifier for shipped machines. The high-end System/390 models known as 9672 were pioneers in employing CMOS CPU technology instead of bipolar logic.

IBM continuously upgraded ESA/390 by integrating new functionalities linked to processor advancements, as detailed in the ESA/390 Principles of Operation documentation.

The IBM z13 marked the final z Systems server to support operating systems running in ESA/390 mode; nevertheless, legacy applications using 24-bit and 31-bit addressing still operate without requiring modifications.

ES/9000

Eighteen different ES/9000 models were introduced on September 5, 1990, available in three distinct formats: water-cooled 9021 units succeeding the IBM 3090, air-cooled standalone 9121 machines, and rack-mounted 9221 models replacing the IBM 4381 and IBM 9370, respectively. Performance levels across these models varied significantly—up to a hundredfold difference—with clock speeds ranging from 67 to 111 MHz (15-9 ns) for the water-cooled 9021, a steady 67 MHz for the air-cooled 9121, and between 26 to 33 MHz (38-30 ns) for rack-mounted 9221 units. Initially, models 120, 130, and 150 of the 9221 series shipped with only the "System/370 Base Option," with an "ESA Option" added later in July 1991. The processors within the 9221 line utilized VLSI CMOS chips engineered in Böblingen, Germany; this design later evolved into the 9672 series.

Among eight water-cooled variants (codenamed H0), six were immediately available but employed processors identical to those in the earlier 3090-J model running at a peak of 69 MHz (14.5 ns), resulting in unchanged performance levels. Their primary enhancements over the 3090-J included optional ESCON connectivity, Sysplex capabilities, and Integrated Cryptographic Features. Only two models—the 900 and 820—featured a completely redesigned architecture (codenamed H2 or Summit), incorporating private split L1 caches of 128+128 KB each, a shared L2 cache of 4 MB (divided as two segments of 2 MB) with an access latency of eleven cycles, improved processor interconnects, multi-level translation lookaside buffers (TLBs), branch target buffers, and operated at a clock speed of 111 MHz (9 ns). These were IBM’s first mainframes since the System/370-195 in 1973 to implement out-of-order execution; however, they uniquely provided full out-of-order processing for both integer and floating-point units while maintaining precise exception handling within a superscalar pipeline. Models 820 and 900 became available in September of 1991—approximately one year after earlier technology-based models—and this architecture was subsequently applied to models such as the 520, 640, 660, 740, and 860.

All three ES/9000 lines received iterative updates throughout the period from late 1993 into early 1994. In February of 1993, an eight-processor model designated as the 982 was launched running at a clock speed of 141 MHz (7.1 ns). Following this release in March came models numbered: 972, 962, 952, 942, 941, alongside air-cooled variants such as the 831, plus rack-mounted units like the 822, 821, and standalone model numbered as well at times as "711." These H5-coded machines doubled their L2 cache size compared to predecessors and enhanced per-processor throughput by roughly thirty percent while integrating hardware-based data compression capabilities—a feature also incorporated into faster versions of air-cooled models like the ES/9000’s standalone unit numbered as "9121."

In April of 1994—coinciding with introduction of CMOS-based new-generation machines under the 9672 series and improvements to rack-mounted systems featuring cycle times approximately forty percent faster plus data compression—IBM unveiled what would become their most powerful bipolar architecture: a ten-processor model labeled as "9X2," boasting performance ratings around approximately four hundred sixty-eight million instructions per second (MIPS).

Reported MIPS values for this model vary depending on sources—from roughly four hundred sixty-five up to more than four hundred eighty-five MIPS—with IBM’s own materials indicating ratings reaching up to four hundred eighty-five MIPS but later adjusting estimates near five hundred ten MIPS. These discrepancies arise due to workload variations and system configurations measured via IBM’s LSPR benchmarking methodology. The theoretical upper bound for sustained MIPS performance on model "9X2" is substantially higher at about two thousand eight hundred seventeen MIPS.

The ES/9000 series established a highly scalable mainframe platform that combined cutting-edge processor designs with adaptable configurations tailored for enterprise computing requirements throughout much of the early to mid-1990s.

Models

ES/9000 water-cooled configurations (9021-###)
Model	CPUs	Sides	Maximum storage (primary + expanded)	Maximum channels (Maximum ESCON)	Release date
H0 (340-based configurations)
720	6	2	0.5+4 GB	128 (64)	September 1990
620	4	2	0.5+4 GB	128 (64)
580	3	1	0.25+2 GB	64 (32)
500	2		0.25+2 GB
340	1		128+1024 MB
330	1		128+512 MB		"available through upgrade only"
H2 (520-based configurations)
900	6	2	1+8 GB	256 (256)	September 1991
860	5				February 1992
820	4				September 1991
740	3	1	0.5+4 GB	128 (128)	February 1992
660	2	2
640	2	1
520	1	1	0.25+2 GB	64 (64)
H5 (711-based configurations)
9X2	10	2	2+8 GB	256 (256)	October 1994
982	8				February 1993
972	7				March 1993
962	6
952	5
942	4
941	4	1	1+4 GB	128 (128)
832	3	2			August1993
831	3	1			March1993
822	2	2
821	2	1
711	1	1	0.5+2 GB	64 (64)

ES/9000 air-cooled standalone configurations (9121-###)
Model	CPUs	Sides	Maximum storage (primary + expanded)	Maximum channels (Maximum ESCON)	Release date
320-based configurations
610	4	2	512+1536 MB	96 (88)	March1992
570	3
490	2
480		1	256+768 MB	48 (44)	March1991
440					March1991
320	1				September1990
260					September1990
210					January1991
190			128+384 MB	32 (28)	March1991
180			512 MB combined capacity	32 (28)	April1992

ES/9000 capabilities

ESCON fiber optic channels
Sysplex technology for system coordination and streamlined administration
Vector Facility: available up to one vector processor per Central Processor in 9021 and 9121 variants, originally introduced on the 3090 to replace the IBM 3838 array processor
Up to one Integrated Cryptographic Feature (ICRF) per side on the 9021 model to accelerate encryption, succeeding the 3848 Cryptographic Unit
(Each Central Processor accommodates a single coprocessor at any moment; the total count of installed Vector Facilities and ICRFs cannot exceed the number of Central Processors)
Later 9021, 9121 (1993), and 9221 (1994) models incorporate data compression hardware

Logical partitioning

Logical Partitions (LPARs), initially exclusive to the IBM 3090, became a standard feature on ES/9000 systems through IBM’s Processor Resource/Systems Manager (PR/SM) hypervisor. This technology allows multiple operating systems to operate simultaneously within isolated partitions. Originally supporting up to seven partitions per electrically separated side, this limit was expanded to ten partitions per side in December 1992 for H2 (520-based) models. For instance, a dual-processor model 660 could host as many as twenty partitions if its sides are electrically isolated.

This capability supports IBM’s vision of "lights-out" operations and improved multi-system management.

9672

Introduced in 1994 as the "Parallel Transaction Server" (alongside the 9673 "Parallel Query Server"), the IBM 9672 series marked a full transition of mainframes to CMOS microprocessors. This represented a strategic move away from bipolar-based ES/9000 models post-1994, with the exception of the 9221. Early iterations were slower than the highest-end ES/9000 units, but subsequent generations evolved into IBM’s most powerful ESA/390 mainframes.

Model	Year Released	CPUs	Performance (MIPS)	Memory (GB)
G1 – 9672-Rn1, Enn, Pnn	1994	1–6	15–66	0.125–2
G2 – Rn2, Rn3	1995	1–10	15–171	0.125–4
G3 – Rn4	1996	1–10	33–374	0.5–8
G4 – Rn5	1997	1–10	49–447	0.5–16
G5 – nn6	1998	1–10	88–1069	1–24
G6 – nn7	1999	1–12	178–1644	5–32

With each generation, CPUs incorporated additional instructions and enhanced performance. The initial three generations emphasized cost efficiency. The fourth generation targeted parity with the final bipolar model (9021-9X2) by raising clock speeds—achieving up to a 70% frequency increase albeit with a minor reduction in performance per cycle. By late 1997, the G4 reached clock rates up to 370 MHz, ranking as the second fastest microprocessor after DEC’s Alpha 21164. Its duplicated execution units contributed to improved fault tolerance.

The G5, launched in September 1998, more than doubled previous performance levels and reestablished IBM’s dominance over rivals such as Hitachi’s Skyline mainframes. Operating at frequencies up to 500 MHz, it introduced support for IEEE 754 floating-point standards. Production scaled rapidly, with the thousandth G5 system shipped roughly three months after manufacturing commenced.

Arriving in May 1999, the G6 utilized copper interconnects, boosting operating frequencies to 637 MHz—outperforming contemporary DEC processors.

Linux distributions gained initial support on G5, Multiprise 3000, and G6 platforms, broadening IBM’s ecosystem compatibility.

Other

In September 1996, IBM introduced the S/390 Multiprise 2000, which was positioned as a more affordable alternative to the 9672 series. This model utilized the same technology found in the 9672 G3 but featured fewer processors—capped at five—and smaller off-chip cache sizes. Both the 9672 G3 and Multiprise 2000 represented the final systems to support the pre-XA System/370 architecture. By October 1997, enhanced versions of the Multiprise 2000 were released, delivering an approximate 11% boost in performance. Later, in September 1999, the Multiprise 3000, built upon the 9672 G5 platform and equipped with PCI buses, made its debut.

The S/390 Integrated Server, positioned below the Multiprise line in terms of entry-level offerings, became available by late 1998. This system evolved from S/390-compatibility adapter cards designed for personal computers and matured into a complete S/390 server configuration, incorporating a Pentium II processor as an I/O coprocessor. Notably, it was the first S/390 server to incorporate PCI technology and delivered performance comparable to the older low-end 9221 model 170, supporting up to 256 MB of memory.

Starting in 1997, IBM also provided the "S/390 Application StarterPak," a development kit aimed at facilitating the creation and testing of mainframe applications.

External links

IBM System/390

History

ES/9000

Models

ES/9000 capabilities

Logical partitioning

9672

Other

See also

External links