HP 3000 Manuals HP 3000 Manuals
System Overview Before describing the options and issues involved in migrating to a 900 Series HP 3000 Computer System, it is important to understand the hardware and software components of the system. The 900 Series HP 3000 family is based on HP Precision Architecture (HP-PA), an architecture founded on the concepts of RISC (Reduced Instruction Set Computer). The operating system for the 900 Series family is MPE/iX (MPE with extended large addressing). HP Precision Architecture HP-PA (Hewlett-Packard Precision Architecture) combines RISC principles with additional features to provide a flexible, expandable architecture and to further increase performance. Features include extended addressing (up to 64-bit virtual addressing), support for coprocessors and multiprocessors, and a memory-mapped I/O system. RISC instructions are implemented directly in hardware to eliminate the system overhead associated with the microcode of conventional systems. Pipelining is enhanced by the uniformity of the HP-PA instructions. Improved performance also results from the memory hierarchy design of the new architecture. For a more detailed discussion of HP-PA, refer to the General Information Manual (5954-7418). MPE/iX MPE/iX is the operating system that runs on 900 Series HP 3000 computer systems. Improvements in hardware allow improvements in the operating system. Along with enhanced functionality and ease of use, it provides greater performance and capacity through a virtually addressed file system and higher availability of data. MPE/iX is a superset of MPE V/E, the operating system that runs on the Series 37 through Series 70 HP 3000 computers. Although MPE/iX offers users a superset of MPE V/E features, some incompatibilities exist due to fundamental differences between the systems software and hardware. MPE/iX provides two environments (modes) for program execution: Compatibility Mode (CM) and Native Mode (NM). Program execution is not restricted to operating entirely in CM or NM; a program operating in one mode can call procedures that operate in the other. This switching between CM and NM is called mixed-mode operation. An application or program executes in CM or NM with no noticeable differences to the user. Switching during mixed-mode operation is also transparent to the user. Compatibility Mode. The CM environment emulates MPE V/E-based machine instructions on a 900 Series HP 3000 computer. This operating mode provides object code compatibility between MPE V/E-based systems and MPE/iX-based HP-PA machines; this means that programs that run on MPE V/E-based systems can run on 900 Series HP 3000 computers. CM uses an emulator which functions as an object code interpreter. At run time, the emulator translates each MPE V/E machine instruction into a functionally equivalent sequence of HP-PA machine instructions. MPE V/E programs restored onto MPE/iX-based systems will run transparently under the emulator. The MPE/iX environment also supports the translation of MPE V/E machine instructions through the Object Code Translator (OCT), a system utility. OCT accepts an MPE V/E program as input, performs an optimized translation of the object code into HP-PA machine instructions, and appends the translation to the end of the MPE V/E program. If you run MPE V/E programs on MPE/iX, you will get better performance using OCT than you will using the emulator. With the emulator, instructions have to be fetched and decoded each time the program is run. You can cut overhead significantly by directly executing object code that OCT has already translated and appended to the program file. The OCT translated file saves both the original program and the translation. This means the resulting file can be executed on both MPE V/E-based and MPE/iX-based systems. It is important to note, however, that it needs more disk space than the original file. For either emulated or translated execution, MPE/iX preserves MPE V/E program and data structures and allows access to most MPE V/E callable intrinsics. The application is still subject to the same addressing limitations found on the MPE V/E-based HP 3000 computers. Native Mode. NM is the natural operating mode of the 900 Series HP 3000 computer. NM allows users to utilize the features that the 900 Series HP 3000 offers, including higher performance and the expanded addressing capabilities of HP-PA. Programs developed and compiled with MPE/iX NM compilers automatically run in NM. Programs developed on MPE V/E-based systems need to be recompiled with the MPE/iX version of compilers in order to run in NM. The ability to recompile MPE V/E applications with MPE/iX compilers provides source code compatibility between the two systems. Mixed Mode. MPE/iX uses the Switch subsystem to operate mixed-mode applications, applications that run in both CM and NM. Switch allows programs executing in NM to call procedures which reside in CM Segmented Libraries (SLs). Switch also allows CM programs to call procedures located in NM Executable Libraries (XLs). The Switch subsystem resolves the differences between NM and CM execution through a set of intrinsics that provide mixed-mode execution access. The switching is transparent to the user. Because MPE/iX can mix modes of execution, applications to be migrated in phases, using CM as an intermediate step between MPE V/E and NM. Phased Migration. You can move MPE V/E programs and data to NM over a period of time, using CM as an intermediate step. Moving everything to CM first is convenient in two ways. First, moving MPE V/E files to CM gives you immediate productivity on the 900 Series HP 3000 family; your applications work right away with little or no modification. Also, you may not be able to move files to NM quickly or easily because of such things as the size of applications, because you have object code but the original source code is lost, or because of language implementation differences. You can recompile some parts to NM and leave others in CM, executing in mixed mode. MPE/iX uses the Switch subsystem moves between modes of execution, so it is an important part of phased migrations. You can migrate database applications in phases, moving code and data separately. Move data directly to NM. Move code to CM; you can use it immediately, because MPE V object code and source code are compatible with CM. Recompile and move the code to NM part-by-part, in phases. Mixed mode operations will switch between NM and CM for you. Figure 2-1 shows a phased migration.Figure 2-1. Summary of Phased Migration