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- UCSD Pascal was a Pascal language system that ran on the UCSD p-System portable, highly machine-independent operating system. The University of California, San Diego Institute for Information Systems developed it in 1978 to provide students with a common operating system that could run on any of the then available microcomputers as well as campus DEC PDP-11 minicomputers. UCSD p-System (Version IV, supplied by SofTech) was one of three operating systems that IBM offered for its original IBM PC; but the p-System never sold very well for the IBM PC, mainly because of a lack of applications and because it was more expensive than the other choices. Before that, IBM used the UCSD p-System as the operating system for its Displaywriter, a microcomputer-based dedicated word processing machine (not to be confused with IBM's DisplayWrite word processing software). Notable extensions to standard Pascal include separately compilable Units and a String type. Both of these extensions influenced the design of the Ada programming language. Some intrinsics were provided to accelerate string processing (e.g. 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. UCSD Pascal was based on a p-code machine architecture. Its 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. The UCSD Pascal p-Machine was optimized for the new small microcomputers with addressing restricted to 16-bit (only 64KB of memory). James Gosling cites UCSD Pascal as a key influence (along with the Smalltalk virtual machine) on the design of the Java virtual machine. 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). Urs Ammann, a student of Niklaus Wirth, originally presented p-code in his PhD thesis (see Urs Aman, On Code Generation in a Pascal Compiler, Software—Practice and Experience, Vol. 7, No. 3, 1977, pp. 391–423). This p-code was optimized for generation by the Pascal programming language, and all the original development was done in UCSD Pascal. 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. Later versions also included additional languages that compiled to the p-code base. For example, 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. UCSD p-System shares some concepts with the more current Java platform. 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. 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. The UCSD Pascal compiler was distributed as part of a portable operating system, the p-System.
- In informatica il P-Code o Pseudo-Code è un codice per la descrizione delle istruzioni di programmi che può essere eseguito da un tipo particolare di interprete chiamato macchina P-Code, equivalente alla virtual machine del linguaggio Java. Il P-Code era il target di alcune implementazioni del linguaggio Pascal (compresa quella realizzata nel 1975 dal suo inventore, Niklaus Wirth): un programma in Pascal non veniva tradotto direttamente in istruzioni macchina, comprensibili direttamente dal processore, ma in istruzioni P-Code. Per eseguire il programma si usava un altro programma in grado di interpretare questo codice. Il P-Code è simile al bytecode ma descrive istruzioni a un livello più alto. Mentre il bytecode funziona a un livello molto basso simile al codice macchina, il P-Code descrive operazioni moderatamente complesse come stampare un messaggio o pulire lo schermo. Alcune implementazioni del BASIC e del Pascal usano P-Code che viene tradotto da un compilatore just-in-time in istruzioni in codice macchina. Questa tecnica permette di eseguire lo stesso programma pseudo-compilato su piattaforme differenti e di semplificare lo studio e la realizzazione dei compilatori di linguaggio. Il Business Operating System (BOS) degli anni 80 era un sistema operativo multi piattaforma progettato per eseguire esclusivamente programmi in P-Code. L'UCSD p-System era un sistema operativo portatile indipentente dalla macchina basato su P-Code. Esistevano versioni realizzate per computer estremamente diversi tra loro, tra i quali, oltre ai grossi sistemi al tempo attivi nelle università, il "Texas Instruments TI99/4A", l'Apple II, e il PC IBM, che lo proponeva come alternativa al CP/M-86 e all'MS-DOS. Il Pascal Microengine era un computer prodotto dalla Western Digital alla fine degli anni 70 in grado di interpretare il P-Code in modo nativo.
- UCSD p-System または UCSD Pascal System とは、UCSD Pascal に基づいた移植性の高いオペレーティングシステムである。1978年、カリフォルニア大学サンディエゴ校（UCSD）で開発された。
- P-Code is een tussencode voor de programmeertaal Pascal. Vroege implementaties van Pascal vertaalden Pascal-code in een machine-onafhankelijke P-Code-representatie. Deze tussenvorm werd vervolgens geïnterpreteerd door een programma dat specifiek was voor een computerarchitectuur. Het gevolg was dat alleen deze compacte interpreter aan de verschillende architecturen aangepast diende te worden. Nadeel was dat de programma's veel langzamer werden, door de extra interpretatielaag. Latere Pascal-compilers genereerden daarom directe native code in de machinetaal van de CPU. Deze programma's konden veel sneller worden uitgevoerd.
- UCSD Pascal eller UCSD p-System var et portabelt operativsystem, som ble utviklet av Institute for Information Systems ved University of California, San Diego i 1978. Operativsystemet kunne kjøre på alle datidens mikrodatamaskiner, deriblant DEC PDP-11. IBM lanserte operativsystemet for den opprinnelige IBM-PC. IBM benyttet også UCSD p-System på den mikrodatamaskin-baserte datamaskinen Displaywriter, som var spesiallaget for tekstbehandling. Operativsystemet var skrevet i en variant av programmeringsspråket Pascal, med trendsettende utvidelser av syntaksen til standard-Pascal. UCSD Pascals datatyper Unit og String påvirket trolig programmeringsspråket Ada. Enkelte innebygde funksjoner (intrinsic functions) akselrerte prosesseringen av strenger og søking gjennom tabeller; andre utvidelser av syntaksen gjorde det mulig for adminstratorer å kompilere operativsystemet med dets egen kompilator.
- O UCSD p-System era o sistema operacional escrito em Pascal da Universidade da Califórnia (University of California Software Distribution - Pascal System). Consistia em um sistema operacional que executava programas em pseudo-código, chamados de p-code, em uma máquina virtual previamente escritos em Pascal. Era um sistema operacional que era muito popular no ínicio dos computadores pessoais, por volta do final de 1970 e ínicio de 1980. Similarmente ao Java nos dia de hoje, foi baseado em uma máquina virtual com um conjunto padrão de instruções de baixo nível. As instruções em pseudo-linguagem de máquina "p-code" eram emulados em hardware diferentes, incluindo os micro-computadores 6502, o 8080, o Z-80, e o PDP-11. Desta forma, o compillador Pascal a partir do p-code poderia gerar um programa que funcionaria em qualquer sistema P(P-System) operando em um Apple II, um Xerox 820, ou um DEC PDP-11. A linguagem mais popular para o Sistema P era o UCSD Pascal. Na verdade, o sistema operacional P era, ele mesmo, escrito em UCSD Pascal, tornando assim o sistema operacional inteiro relativamente portátil entre plataformas diferentes. O p-Sytem foi também um dos três sistemas operacionais originais do IBM PC, mas perdeu espaço para o MS DOS devido a, entre outros fatores, problemas comerciais e de licenciamento. O Museu UCSD P-SYSTEM
- Файл:UCSD1. png Экран Редактора в UCSD p-System (UCSD Pascal), Apple II Файл:UCSD3. png Экран Редактора в UCSD p-System (UCSD Fortran), Apple II Файл:UCSD2. png Экран Файлера в UCSD p-System, Apple II UCSD p-System — одна из первых реализаций виртуальной машины (p-машины) на базе интерпретатора байт-кода для создания аппаратно-независимой среды программирования.
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- UCSD Pascal was a Pascal language system that ran on the UCSD p-System portable, highly machine-independent operating system. The University of California, San Diego Institute for Information Systems developed it in 1978 to provide students with a common operating system that could run on any of the then available microcomputers as well as campus DEC PDP-11 minicomputers.
- In informatica il P-Code o Pseudo-Code è un codice per la descrizione delle istruzioni di programmi che può essere eseguito da un tipo particolare di interprete chiamato macchina P-Code, equivalente alla virtual machine del linguaggio Java.
- UCSD p-System または UCSD Pascal System とは、UCSD Pascal に基づいた移植性の高いオペレーティングシステムである。1978年、カリフォルニア大学サンディエゴ校（UCSD）で開発された。
- P-Code is een tussencode voor de programmeertaal Pascal. Vroege implementaties van Pascal vertaalden Pascal-code in een machine-onafhankelijke P-Code-representatie. Deze tussenvorm werd vervolgens geïnterpreteerd door een programma dat specifiek was voor een computerarchitectuur. Het gevolg was dat alleen deze compacte interpreter aan de verschillende architecturen aangepast diende te worden. Nadeel was dat de programma's veel langzamer werden, door de extra interpretatielaag.
- UCSD Pascal eller UCSD p-System var et portabelt operativsystem, som ble utviklet av Institute for Information Systems ved University of California, San Diego i 1978. Operativsystemet kunne kjøre på alle datidens mikrodatamaskiner, deriblant DEC PDP-11. IBM lanserte operativsystemet for den opprinnelige IBM-PC. IBM benyttet også UCSD p-System på den mikrodatamaskin-baserte datamaskinen Displaywriter, som var spesiallaget for tekstbehandling.
- O UCSD p-System era o sistema operacional escrito em Pascal da Universidade da Califórnia (University of California Software Distribution - Pascal System). Consistia em um sistema operacional que executava programas em pseudo-código, chamados de p-code, em uma máquina virtual previamente escritos em Pascal. Era um sistema operacional que era muito popular no ínicio dos computadores pessoais, por volta do final de 1970 e ínicio de 1980.
- Файл:UCSD1. png Экран Редактора в UCSD p-System (UCSD Pascal), Apple II Файл:UCSD3. png Экран Редактора в UCSD p-System (UCSD Fortran), Apple II Файл:UCSD2.
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