488 Part 2½ Regions of Computer Space Section 7 ½ Language-Based Computers

information has been transformed into a data structure that is easier to manipulate than source language. The internal form also contains enough information to recreate the original source language statement.

The BASIC machine is implemented by ROM programs for a dual-processor system. Each processor executes a minicomputer instruction set (similar to that of the HP 2116 minicomputer) that is implemented entirely with LSI technology. Special-purpose processors for I/O and BCD arithmetic act as extensions to the main processors.

The final level of abstraction is the microcoded machine that implements an HP 2116-like instruction set. Chapter 31 describes the top two levels of abstraction in detail.

This paper is included for several reasons. It characterizes the desk-top computing (or personal computing) environment as it differs from other environments, such as that of minicomputers. It contains the details of another minicomputer instruction set as well as instruction sets for special-purpose processors (e.g., processors for I/O and BCD arithmetic). Finally, since the HP 9545A is a dedicated, single-user machine, performance is secondary to ease of use. Without strict performance requirements, the BASIC language machine can be implemented in software ROM on top of a minicomputer ISP.
 

IBM System/38

The IBM System/38 is a business-oriented data processing system introduced in late 1978. The System/38 standardizes the hardware interface between the traditional ISP level and a higher-level language. Instructions have been implemented whose functionality has traditionally been reserved for operating-system software. Examples of this functionality include queue-driven task management, record-level data management, process management, and object-oriented memory management. Although the first release of the System/38 software only provided RPG and Interactive Data Base Utilities, the Control Program Facility provides a uniform interface to the system hardware upon which other language environments can be built.

While the System/38 is essentially a Type 1(a) system, it deserves special note for several reasons:

• It provides hardware support for high-level-language concepts and may be a harbinger of future ISPs designed to support multiple high-level languages.
• It is the only example in this book of an object-oriented memory management system fully supported in hardware (see Part 2, Sec. 2). Since the access path to objects is machine-controlled, effective authority enforcement and automatic serialization of concurrent operations on the same object are achieved.
• The concept of architecture has been pushed up into the software levels, paving the way for future migration of even more functionality into microcode and hardware.
• A large, 48-bit virtual address is efficiently supported by a hash table lookup into a physical page directory.
• Programs are translated into microcode before execution.
• Program-variable attributes allow automatic data-type conversions.

References

Chu and Cannont [1976]; Rice and Smith [1971]; Weber [1967]; Wirth and Weber [1966a,b].