IBM System/38
IBM System/38

The System/38 was a midrange computer server platform manufactured and sold by the IBM Corporation. The system offered a number of innovative features, and was the brainchild of Frank Soltis and Glenn Henry. IBM announced the System/38 in 1978.[1] Developed under the code-name "Pacific", it was made commercially available in August 1979. The System/38 was oriented toward a multi-user system environment.


The midrange predecessors to the System/38 included the System/3, System/32, and System/34. The System/38 offered more capacity than the previous System/34. The System/38 chronologically preceded the System/36, which was a successor to the System/34.

The System/38 was nearly called the System/380, and the AS/400 was nearly called the System/40.[]

The System/38 was superseded by the AS/400 (which also supported System/36 data & programs, at least to some extent). The AS/400 was primarily a re-marketing of the System/38, with some updates to the operating system. S/38 programs (with 'observability' intact) can still run on the AS/400 and successor systems.

The AS/400 evolved into the iSeries, which in turn evolved into the System i (although the 'evolution' does include significant enhancements to hardware and operating system capabilities, the name change is usually considered more of an evolution in marketing). The System/38 legacy lives on in the enterprise-class IBM Power Systems series, which superseded System i in 2008, and which can run IBM i as well as AIX and Linux.

By contrast, competing proprietary computing architectures from the early 1980s such as Wang VS and Hewlett Packard's HP 3000 have long been discontinued without a compatible upgrade path.

In hindsight, the System/38's architecture was probably too demanding of the hardware of the era. When first launched, it struggled under the overhead of the software and operating system, which consumed almost 60 MB on disk, a vast sum at the time, leading some wags to suggest that the pre-announce code name for the series, PACIFIC, was actually an acronym meaning "Performance Ain't Critical If Function Is Complete."

Decades later, the same software, originally dismissed by some critics[who?] as a momentary aberration, runs better than ever on many thousands of modern iSeries and IBM/i systems within commercial and government enterprises of all types and sizes.[]

Hardware characteristics

Two hard disks

The IBM 5381 System Unit contained processor, main memory, disk storage, a diskette magazine drive, and a system console with keyboard and a display. 5381 was available in Model 100 and Model 200.

The IBM 5382 System Unit was physically identical to 5381, but had more powerful processors, more memory, and more disk storage. 5382 was available in Models 300, 400, 500, 600, and 700.

Processing unit

The system included a central processing unit with 512K, 768K, 1024K, 1280K, or 1536K bytes of main storage, It included a memory management unit supporting demand paging, used by the system software to implement a single-level store architecture.

System console keyboard/display

IBM System/38 console

The System/38 console included a keyboard and a display screen with 16 lines. The 64 characters per line were larger than those displayed on the locally attached 5250 terminals. The keyboard was used by the system operator when entering Control Language commands.

Diskette magazine drive

The diskette magazine drive was standard on all models.

Control Program Facility

The operating system of the System/38 was called CPF, for "Control Program Facility". CPF is not related to SSP, the operating system of the IBM System/34 and System/36.

The System/38 also has the distinction of being the first commercially available IBM Midrange computer to have a database management system (DBMS) integrated into the operating system.

The operational control language of the System/38 was called CL, for "Control Language". CL programs, similar in concept to shell scripts, could be compiled and executed natively.

The System/38 had 48-bit addressing, which was unique for the time, and a novel integrated database system.

The System/38 also had security built in as part of its architecture. Each object or library could have access controlled on a user-by-user basis. This has been continued and expanded throughout the AS/400 and iSeries computer lines.

Technology independence

The System/38 and its descendants are the only commercial computers ever to use a machine interface architecture to isolate the application software and most of the operating system from hardware dependencies, including such details as address size and register size.

Compilers for System/38 and its successors generate code in a high-level instruction set (originally called MI for "Machine Interface", and renamed TIMI for "Technology Independent Machine Interface" for AS/400). MI/TIMI is a virtual instruction set; it is not the instruction set of the underlying CPU.

Unlike some other virtual-machine architectures in which the virtual instructions are interpreted at runtime (see P-code machine), MI/TIMI instructions are never interpreted. They constitute an intermediate compile time step and are translated into the processor's instruction set as the final compilation step. The MI/TIMI instructions are stored within the final program object, in addition to the executable machine instructions. If a program is moved from a processor with one native instruction set to a processor with another native instruction set, the MI/TIMI instructions will be re-translated into the native instruction set of the new machine before the program is executed for the first time on the new machine.

As a result, it is possible for a program originally developed on a System/38 to run on current IBM i hardware without ever being recompiled. This capability allowed the AS/400 to migrate from CISC (Complicated Instruction Set Computer) to RISC (Reduced Instruction Set Computer) in the 1990s. If the MI/TIMI instructions existed in a compiled program, a relatively simple re-translation created a new program native to the new hardware.

Distributed Data Management

In 1986, System/38 announced support for Distributed Data Management Architecture (DDM). Such a middleware in the context of a distributed system is the software layer that lies between the operating system and applications. This enabled System/38 programs to create, manage, and access record-oriented files on remote System/36, System/38, and IBM mainframe systems running CICS. It also allowed programs on remote System/36 and System/38 computers to create, manage, and access files of a System/38.

Programming languages

Languages supported on the System/38 included RPG III, COBOL, BASIC, and PL/I.


IBM sold an estimated 20,000 System/38s within the first five years of availability, according to articles published in industry magazines NEWS 34/38 and Midrange Computing. Although billed as a minicomputer, the S/38 was much more expensive than IBM's established best-selling System/34, and its replacement, the System/36. Of equal importance was the difficulty of upgrading from, say, a System/34 to a S/38. Although the machines had some similarities, such as twinax peripherals and RPG programming languages, in reality they were very different. IBM tacitly acknowledged this by bringing out the System/36 - an upgraded System/34 - after the launch of the S/38.

In the marketplace, IBM thus found itself with three overlapping, but incompatible, ranges. The System/34/36, the System/38 and the mainframe /360 architecture (that the System/38 was originally designed to replace). Digital Equipment Corporation, at that time one of IBM's main competitors, was able to exploit this by offering a wide range of products based on a single architecture. IBM's counter to this, the 9370 or 'baby mainframe', was a commercial failure.


  1. ^ "IBM Archives: 1970s, year 1978". IBM.

Further reading

External links

  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.



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