FIFTH - virtual machine, operating system, programming language

Program author:
    Svjatoslav Agejenko
    Homepage: http://svjatoslav.eu
    Email: svjatoslav@svjatoslav.eu

This software is distributed under GNU GENERAL PUBLIC LICENSE Version 2.

Introduction

Fifth is programming lanquage & operating system, running on
virtual CPU, with custom instruction set. It is much like
Charles Chunk Moore's Forth, it also uses stack architecture,
and many commands are similar. Basically I got familiar with
concepts of Forth, and being inspired created my own system.

Note:

Current implementation does not support object oriented programming.
While working on Fifth I got lots of cool new ideas that require reimplementation
of everything.
 
Currently I try to implement those new ideas in the project called
    Sixth.



Screenshots

Read more about:

  Virtual CPU

  Built-in commands

  Additional commands, realized as loadable modules

  Example Fifth source file - text editor 


    
Installation

Just unpack all files, witout altering original directory structure,
somewhere in your hard disk. For example: C:\MISC\FIFTH\....
To run fifth you need minimally just 2 files.
emulator itself ( EMULATOR.EXE or EMULATOR.COM ), and
virtual disk file ( DISK.RAW ).
Read more about distribution directory layout.



    
Software/Hardware/Human requirements


Software:
    MS-DOS 6.22, with HIMEM.SYS loaded.
	Mouse driver if you have a mouse.
	Does work only when CPU is in real mode.
	To recompile ASM sources I used FASM (Flat Assembler).
	I ran QBasic utilities on QB 4.5 .
	VESA support by BIOS, or external driver (UNIVBE).

Hardware:
    Minimum CPU 386.
	64 KB free RAM below 640KB,
	2 MB of free XMS.
	VESA compatible video card.

Human:
    Beginner level Forth knowledge is recommended.
	Enthusiasm.



    
Numbers representation



Fifth uses hexdecimal number representation as primary.
Numbers shape is formed by dividing a square into four parts.
And manipulating their color (black or white).



    
Disk file map, and it's data structures


Core and high-level boot code is stored outside of the filesystem to allow
easy access to it, at early booting time, when filesystem is not yet
initialized.

			disk allocation:

offset	length	description

0	~4 Kb	Fifth core
4  Kb	~32Kb	high-level boot code
37 Kb	~65Kb	FAT
101Kb	~16MB	filesystem data area

			FAT entry format:

-2	last sector
-1	empty sector
0 --  .. pointer to next block

			file entry format

offset	length	description

0	4	extension
4	16	name
20	4	entry point
24	4	size
28	4	last modification time



    
Core architecture


Fifth core is simply some amount of already compiled into machine code
and linked together modules (entries in other words). In compilation
process modules is compiled one by one and simply stored on top of
already existing and growing core. Separately from core is kept
dictionary, this is special list that contain names of compiled modules,
variables etc. and they locations in core. Constants use dictionary space
only. Random word can be removed from dictionary at any time. Currently
dictionary can contain at most 1000 entries.


			dictionary entry format

offset	length	description

0	4	 0 < previous entry
		 0 = last
		-1 = empty
4	15	module name string
19	1	entry type
20	4	entry data

Core headers as linked list of module names make up something like dictionary.
When some entry address is needed compiler can quickly run through headers
backwards and find needed entry.

			Possible module types

type	description	"execute" action

0	data		compile "num" instruction
			with address to module
1	submodule	compile "call" instruction
			with address to module
2	imm. submodule	immediately call to module


		Memory map: (average)

		
0	~4096	core
1500000 ~32000	highlevel Fifth boot code
200000h 	core startup messages area
5200000 	end of dynamic memory space



    
Fifth source format


Fifth uses a different character table and codes than ASCII.
I call it FSCII (Fifth Standard Code for Information Interchange)
for example space character is not 32 but 255 instead.
I plan to use mainly HEX numbers, and create new characters
to represent numeric values. So typical nemric characters "0123..."
is treated like ordinary letters.

	FSCII:

DEC	HEX	function

0 - 15	0 - F	HEX numbers
252	FC	backspace
253	FD	tabulator (TAB)
254	FE	carriage return (CR)
255	FF	space

else		ordinary characters, like in ASCII.