IBM 4300

IBM 4300 series

Company type	Product line
Industry	Computer hardware
Founded	1979
Defunct	1992
Area served	Worldwide
Products	Mid-range mainframe computers compatible with System/370 architecture (models 4331, 4341, 4361, 4381)

The IBM 4300 series represents a line of mid-range computers compatible with the System/370 architecture, marketed between 1979 and 1992. Engineered to operate with relatively low power consumption and cooling requirements, these systems did not necessitate specialized data center infrastructure. This design choice allowed organizations to provide internal IBM computing resources more economically compared to commercial time-sharing services. Instead of conventional keyboard/printer consoles, all 4300 models utilized display consoles such as the 3278-2A, 3279-C, or 3205.

Processors

The series included several processors—4331, 4341, 4361, and 4381—each available in multiple models or model groups (for example, 4341-1 or 4381-MG1). Announced in 1987, the 4381-13 through 4381-24 targeted entry-level users of the 370-XA architecture, offering performance levels positioned between the IBM 9370 and IBM 3090 systems.

Certain models supported dual-CPU symmetric multiprocessing, including the 4381-MG3, MG14, MG24, and MG92 variants. Additional model groups were designated as 1, 2, 11, 12, 13, 21, 22, 23, 90, and 91.

Processor	Model group	Announcement date	Withdrawal date	Maximum memory	Approximate relative performance
4331		1979	1981	8 MB	Equivalent to 4 × 370/115
4341		1979	1986	16 MB	Roughly 3.2 × 370/138
4361		1983	1987	12 MB	About 3 × performance of the 4331
4381	1	Sep 15, 1983	Feb 11, 1986	16 MB	Approximately equal to 9 × the performance of the 4341
2 |Sep15,1983 |Feb11,1986 |32 MB |Similar to model group 1 |
3 |Oct25,1984 |Feb11,1986 |32 MB |
11 |Feb11,1986 |
12 |Feb11,1986 |
13 |Feb11,1986 |
14 |Feb11,1986 |
21 |May19,1987 |
22 |May19,1987 |
23 |May19,1987 |
24 |May19,1987 |
91E |Feb15,1988 |
92E |Feb15,1988 |
90E |Feb7,1989 |

IBM 4331

Introduced on January 30, 1979 alongside the IBM 4341, the IBM 4331 incorporated an internal adapter capable of supporting up to sixteen units of two new direct-access storage device (DASD) types:

• The IBM 3310 offered around "64.5 million characters" of storage capacity with sealed disk packs designed to reduce contamination or damage.
• The IBM 3370 provided higher storage capacity—up to "571 million characters"—and was compatible with the IBM 4341 system.

The IBM 4331 was officially withdrawn from the market on November 18, 1981.

IBM 4341

Launched simultaneously with the IBM 4331 on January 30, 1979, the IBM 4341 also included an integrated adapter supporting up to sixteen IBM 3370 DASD devices but did not accommodate the lower-capacity IBM 3310. This model introduced Extended Control Program Support features: VM (ECPS:VM), VS1 (ECPS:VS1), and Virtual Storage Extended (ECPS:VSE). Additionally, the later variant known as the 4341-2 added ECPS:MVS capability to enhance support for System/370 extended functions.

On October 20, 1982, IBM expanded the product line with a new entry-level model (Model Group 9) and a high-end Model Group 12 that incorporated Dual Address Space (DAS) functionality. The IBM 4341 was discontinued on February 11, 1986.

IBM 4321

The IBM 4321 was officially introduced on 18 November 1981.

IBM 4361

The IBM 4361 Model Groups 4 and 5 were unveiled on 15 September 1983, with Model Group 3 following on 12 September 1984.

Enhanced Capabilities

Significant optional enhancements available for the 4361 included:

• Auto-Start—this feature allowed the processor to be powered on automatically either via telephone using the Remote Operator Control Facility or at predetermined times, performing system power-up, microcode loading, clock setting, and startup initiation.

APL Keyboard Support

• A Workstation Adapter was provided to accommodate terminals equipped with APL keyboards and support for APL syntax and symbols.

High-Precision Arithmetic Facility

Expanding upon floating-point functionalities inherited from System/360, this sophisticated arithmetic option, inspired by the Karlsruhe Accurate Arithmetic methodology, was offered for the 4361.

The IBM 4361 was retired from the market on 17 February 1987.

IBM 4381

The IBM 4381 represented a robust mid-range mainframe cooled by air, distinguished by a pioneering control panel housing 64 multi-chip module ceramic units paired with an air-cooled heat sink.

Model Groups 1 and 2 were launched on 15 September 1983 and subsequently withdrawn on 11 February 1986.

Model Group 3 appeared on the market on 25 October 1984 and was withdrawn alongside the earlier models on 11 February 1986.

Later, Model Groups 11 through 14 were announced on 11 February 1986.

Model Groups 21 to 24 became available on 19 May 1987 and were phased out by 19 August 1992.

Operating Systems

New versions supporting the IBM 4300 series as well as other System/370-compatible processors included:

• Disk Operating System/Virtual Storage Extended (DOS/VSE)
• Virtual Machine Facility/370 (VM/370) Release 6
• Operating System/Virtual Storage 1 (OS/VS1) Release 7

For the IBM 4321 and IBM 4331 models:

• Small Systems Executive/Virtual Storage Extended (SSX/VSE), a simplified iteration of DOS/VSE optimized for these systems.

Additional Information

• Hughes Aircraft Company was the initial IBM client to deploy Endicott's first IBM 4341 processor.
• The IBM 4331 Model 2 was engineered in Boeblingen and manufactured at Endicott.
• Development of the IBM 4341 Model 2 was conducted by the intermediate systems group with production handled by SPD in Endicott.
• Subsequent processors beginning with the IBM 4381 involved collaborative development and manufacturing across locations including Endicott, Havant, Boeblingen, Valencia, and Sumare.

See also

• List of IBM products
• IBM System/360
• IBM System/370
• Karlsruhe Accurate Arithmetic (KAA) implementation for the IBM 4361
• Molly-guard

Further reading

• (Information regarding the design and architecture of the IBM 4381.)

External links

• Request access to Living Computers: Museum + Labs IBM 4361.