![]() UCSD p-System began around 1974 as the idea of UCSD's Kenneth Bowles, who believed that the number of new computing platforms coming out at the time would make it difficult for new programming languages to gain acceptance. #Manual de free pascal portableThe UCSD Pascal compiler was distributed as part of a portable operating system, the p-System. Likewise both systems allow the virtual machine to be used either as the complete operating system of the target computer or to run in a "box" under another operating system. Both use a virtual machine to hide operating system and hardware differences, and both use programs written to that virtual machine to provide cross-platform support. UCSD p-System shares some concepts with the later Java platform. Later, TeleSoft (also located in San Diego) offered an early Ada development environment that used p-code and was therefore able to run on a number of hardware platforms including the Motorola 68000, the System/370, and the Pascal MicroEngine. For example, Apple Computer offered a Fortran Compiler (written by Silicon Valley Software, Sunnyvale California) producing p-code that ran on the Apple version of the p-system. Later versions also included additional languages that compiled to the p-code base. Each hardware platform then only needed a p-code interpreter program written for it to port the entire p-System and all the tools to run on it. The UCSD p-code was optimized for execution of the Pascal programming language. The UCSD implementation changed the Zurich implementation to be "byte oriented". Urs Ammann, a student of Niklaus Wirth, originally presented a p-code in his PhD thesis, from which the UCSD implementation was derived, the Zurich Pascal-P implementation. UCSD p-System achieved machine independence by defining a virtual machine, called the p-Machine (or pseudo-machine, which many users began to call the "Pascal-machine" like the OS-although UCSD documentation always used "pseudo-machine") with its own instruction set called p-code (or pseudo-code). James Gosling cites UCSD Pascal as a key influence (along with the Smalltalk virtual machine) on the design of the Java virtual machine. The UCSD Pascal p-Machine was optimized for the new small microcomputers with addressing restricted to 16-bit (only 64 KB of memory). #Manual de free pascal fullIts contribution to these early virtual machines was to extend p-code away from its roots as a compiler intermediate language into a full execution environment. UCSD Pascal was based on a p-code machine architecture. scanning in an array for a particular search pattern) other language extensions were provided to allow the UCSD p-System to be self-compiling and self-hosted. Some intrinsics were provided to accelerate string processing (e.g. Notable extensions to standard Pascal include separately compilable Units and a String type. (The Displaywriter's native operating system had been developed completely internally and was not opened for end-user programming.) Previously, IBM had offered the UCSD p-System as an option for Displaywriter, an 8086-based dedicated word processing machine. The p-System did not sell very well for the IBM PC, because of a lack of applications and because it was more expensive than the other choices. PC Magazine denounced UCSD p-System on the IBM PC, stating in a review of Context MBA, written in the language, that it "simply does not produce good code". It predicted that users would be able to use applications they purchased on future computers running p-System advertisements called it "the Universal Operating System". Vendor SofTech Microsystems emphasized p-System's application portability, with virtual machines for 20 CPUs as of the IBM PC's release. #Manual de free pascal PcThe first was UCSD p-System, with IBM PC DOS and CP/M-86 as the other two. There were three operating systems that IBM offered for its original IBM PC. The operating system became known as UCSD p-System. In 1977, the University of California, San Diego (UCSD) Institute for Information Systems developed UCSD Pascal to provide students with a common environment that could run on any of the then available microcomputers as well as campus DEC PDP-11 minicomputers. ![]()
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