 | |
 IBM System/38 | |
| Manufacturer | IBM |
|---|---|
| Release date | 1978; 47 years ago (1978) |
| Discontinued | 1988 |
| Operating system | Control Program Facility |
| Dimensions | 1260x1775x750mm[1] |
| Predecessor | IBM System/34 |
| Successor | IBM AS/400 |
| Related | IBM System/36 |
TheSystem/38[2][3] is a discontinuedminicomputer andmidrange computer manufactured and sold byIBM. The system was announced in 1978.[4] The System/38 has48-bit addressing, which was unique for the time, and a novelintegrated database system. It was oriented toward amulti-user system environment. At the time, the typical system handled from a dozen to several dozenterminals. Although the System/38 failed to displace the systems it was intended to replace, its architecture served as the basis of the much more successfulIBM AS/400.[5][6]
The System/38 was introduced on October 24, 1978 and delivered in 1980. Developed under the code-name "Pacific", it was made commercially available in August 1979. The system was designed by a number of engineers includingFrank Soltis andGlenn Henry and offered a number of innovative features. The architecture shared many similarities with the design of the failedIBM Future Systems project, including thesingle-level store, the use ofmicrocode to implement operating system functionality, and the Machine Interface abstraction.[5][6][7] It had been developed over eight years byIBM's laboratory inRochester, Minnesota.[8] The president of IBM's General Systems Division (GSD) said at the time: "The System/38 is the largest program we've ever introduced in GSD and it is one of the top three or four largest programs ever introduced in IBM."[9]
The system was designed as a follow-on for theSystem/3,[9] but it is not compatible with those computers. The predecessors to the System/38 include the System/3 (1969),System/32 (1975), andSystem/34 (1977). In 1983 theSystem/36 was released as a low-end business computer for users who found the System/38 too expensive for their needs. The System/38 was succeeded by theIBM AS/400 midrange computer family in 1988, which originally used a processor architecture similar to the System/38, before adoptingPowerPC-based processors in 1995.[5]
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The IBM 5381 System Unit contains 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 is physically identical to 5381, but with more powerful processors, more memory, and more disk storage. 5382 was available in Models 300, 400, 500, 600, and 700.
Users typically interacted with the system throughIBM 5250 series terminals. In 1984, IBM added the ability to attach graphics-oriented terminals that previously required a mainframe.[10]
The system includes acentral processing unit with 512K, 768K, 1024K, 1280K, or 1536K bytes of main storage. The processor is implemented across twenty-nineSchottky TTLLSI chips mounted on a 10x15" circuit board.[11] It includes amemory management unit supportingdemand paging, used by the system software to implement asingle-level store architecture.
The System/38 CPU features a48-bit address space, which was selected as a compromise between64-bit addressing, which certain IBM engineers wanted for the sake of future proofing, and32-bit addressing, which other engineers wanted for cost saving purposes.[5]
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The System/38console incorporates a keyboard and a display screen with 16 lines of 64 characters, inconsistent with the locally attached5250 terminals, which are either 12x40 or 24x80, depending on model. The keyboard is available to the system operator to enter Control Language commands.
The diskette magazine drive is standard on all models.
The System/38 and its descendants use a machine interface architecture to isolate theapplication 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 known as theMachine Interface, or MI. MI is a virtual instruction set; it is not the instruction set of the underlying CPU. MI operates onobjects instead of traditional memory addresses or registers.[12]
Unlike some other virtual-machine architectures in which the virtual instructions are interpreted at runtime (seeP-code machine), MI instructions are never interpreted. They constitute an intermediate compile time step and aretranslated into the processor's instruction set as the final compilation step. The MI 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 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.
The TIMI (Technology Independent Machine Interface) of OS/400 is a backwards compatible extension of the System/38 MI. As a result, it is possible for a program originally developed on a System/38 to run on currentIBM i hardware without ever being recompiled.[5]
IBM referred to all code below the Machine Interface layer of the System/38 architecture asmicrocode, and treated it as part of the hardware.[11] The term microcode was used to cover a wide array of low-level code, ranging from traditionalmicrocode, up to functionality typically associated with thekernels of other operating systems, as well as the implementation of the integrated database.[13] There were two levels of microcode in the System/38:
The use of the term microcode stemmed from a 1969 antitrust case against IBM which resulted in IBM unbundling software from its hardware products (i.e. requiring software to be purchased separately from the hardware). By treating the low level code of the System/38 as part of the hardware, IBM was able to treat the MI as the native instruction set of the System/38, and thus have the freedom to change the IMPI and microcode as the underlying hardware evolved.[5] Early AS/400 systems inherited the System/38 microcode structure, but the term microcode was dropped, leading IBM to rename the layers to theVertical Licensed Internal Code andHorizontal Licensed Internal Code.
The operating system of the System/38 is theControl Program Facility (CPF). CPF is not related to theSystem Support Program operating system of the IBM System/34 and System/36. CPF objects are files, programs, message queues, user profiles, and libraries. While CPF is considered to be the operating system of the System/38, it sits on top of the System/38 Machine Interface layer, and consequently much of the traditional operating system functionality of the platform is implemented in the Horizontal and Vertical Microcode.[5]
The System/38 also has the distinction of being the first commercially available IBMMidrange computer to have adatabase management system (DBMS) integrated into the operating system.
The operational control language of the System/38 is calledCL, forControl Language. CL programs, similar in concept toshell scripts, can becompiled and executednatively.
The System/38 was designed with security built in as part of its architecture. Each object or library can have access controlled on a user-by-user basis. This has been continued and expanded throughout the AS/400 and iSeries computer lines.
The System/38 was superseded by the AS/400, which also provided compatibility with System/36 data and software.[17] S/38 programs with 'observability' intact, that is source code embedded within the compiled binary executive at the expense of larger compiled object sizes, can still run on the AS/400 and successor systems as the restore option incorporates a recompile for the then back-version source. However, most proprietary vendor application libraries of objects were compiled without such 'observability' and require original vendor replacement and consequent expense when upgrading to an AS/400. Pricing at the time was tiered, the same exact software, but priced based upon the model, its speed and capacity, of the system to be installed upon.
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 aminicomputer, 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 a System/34 to a S/38. IBM tacitly acknowledged this by bringing out the System/36 – an upgraded System/34 – after the launch of the S/38. Although the System/38 did not sell in large numbers, it commanded a higherprofit margin than IBM's other midrange systems, and thus was a profitable product line for IBM.[6]
In the marketplace, IBM thus found itself with three overlapping, but incompatible, ranges. The System/34, the System/38 and the mainframeSystem/370 architecture.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 - specifically theVAX architecture.[18] IBM's counter to this, the9370, was a commercial failure, and at that time,The New York Times wrote, sales of the System/36 and System/38 were "lagging."[19]
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