Fifth - virtual machine, operating system, programming language
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1 !Project deprecated!
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
System is built many years ago when I was still using DOS as a primary operating system.
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.
Read more about:
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
4 Software/Hardware/Human requirements
- 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).
- Minimum CPU 386.
- 64 KB free RAM below 640KB,
- 2 MB of free XMS.
- VESA compatible video card.
- Beginner level Forth knowledge is recommended.
- Lots of enthusiasm.
5 Numbers representation
Because I can define everything, starting from CPU, why not try also alternative and unique number representation ?
Fifth uses its hexdecimal number representation as primary. Numbers shape is formed by dividing a square into four parts. And manipulating their color (black or white).
6 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.
6.1 disk allocation
|0||~4 Kb||Fifth core|
|4 Kb||~32Kb||high-level boot code|
|101Kb||~16MB||filesystem data area|
6.2 FAT entry format:
|0 --||.. pointer to next block|
6.3 file entry format
|28||4||last modification time|
7 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.
7.1 dictionary entry format
|0||4||0 < previous entry|
|0 = last|
|-1 = empty|
|4||15||module name string|
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.
7.2 Possible module types
|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|
7.3 Memory map: (average)
|1500000||~32000||highlevel Fifth boot code|
|200000h||core startup messages area|
|5200000||end of dynamic memory space|
8 Fifth source format
Fifth uses a different character table and codes than ASCII (still almost similar). 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.
|0 - 15||0 - F||HEX numbers|
|254||FE||carriage return (CR)|
|else||ordinary characters, same as in ASCII.|