ucsd-psystem-fs 1.6

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The ucsd-psystem-fs package is composed of several utility programs which may be used to manipulate and mount UCSD p-Systems disk images.

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About This Project

This project has been successfully tested against several disk image formats. All of the disk formats are automatically detected at run time, no guessing by the user is required. The formats supported include:

• Non-interleaved disk images work correctly, for any valid size. This gives the best performance, as you would expect.
• Single and redundant directory contents work.
• Apple ][ Pascal 140KB interleaved disk images work correctly. This was tested against the system disk images at ftp://ftp.mayn.de/ pub/ really_old_stuff/ mirrors/ apple.asimov.net/ programming/ apple_pascal/
• Simple 800KB disk images work. This was tested against the disk images at http://apple2.callapple.org/ software/ tribby/ apascal.html
• Offset interleaved 256KB disk images (PDP11?) work. This was tested against the disk images at http://www.bitsavers.org/ bits/ UCSD_Pascal/ ucsd_II.0/

IIRC, the original UCSD p-System did not permit more than one file being open for writing at the same time. Files in this file system are represented by a single continuous disk extent. This implementation uses the Buffer Gap algorithm, found in many text editors, to manage file extents being written. This implementation can cope with two (or more) files open for writing at the same time, however performance will be impacted as disk blocks will constantly be shuffled back and forth as the gap is moved to the end of each of the files being written.

Ancient History

Like today's Java, it was based on a “virtual machine” with a standard set of low-level, machine- language-like “p-code” instructions that were emulated on different hardware, including the 6502, the 8080, the Z-80, and the PDP-11. In this way, a Pascal compiler that emitted p-code executables could produce a program that could be run under the P-System on an Apple II, a Xerox 820, or a DEC PDP-11.

The most popular language for the P-System was UCSD Pascal. In fact, the P-System operating system itself was written in UCSD Pascal, making the entire operating system relatively easy to port between platforms.

By writing a p- code interpreter in the platform's native assembly language, and a few minimal hooks to operating system functions for the file system and interacting with the user, you could move a p-code executable from another system and run it on the new platform. In this way, the p-code generated on one computer could be used to bootstrap the port of the P-System to another computer.

From the Jefferson Computer Museum web site.

See Also

Jefferson Computer Museum

This site has links and history for the UCSD p-System.

Mailing List

In 2004 Yahoo! group devoted to UCSD Pascal was started.

Mario Klebsch

has written a p-code interpreter in C. It should be portable to all POSIX systems. It can even display TurtleGraphics in X11.

UCSD

UCSD officially released some of the source.

apple2fs

Here is another Linux file system, for Linux 2.4 series kernels.

Search Google

You make like to search Google for more UCSD p-System information.

Sister Projects

	UCSD Pascal Cross Compiler: You can cross compile your UCSD Pascal code on Unix to create p-Machine object code.
	UCSD p-System User Manual: A modern reconstruction of the UCSD p-System User Manual is available as HTML.

How it Works