Os8088: A powerful Mac-like OS for the IBM XT, 286, 386
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A Macintosh System 1-style desktop for the Intel 8086, written entirely in real-mode assembly and booted from a floppy. Overlapping windows, pull-down menus, a serial mouse, loadable programs -- and pre-emptive multitasking, which the real 1984 Macintosh never had.
os8088 boots from the first sector of a floppy into a graphical desktop. There is no DOS underneath it and no command line anywhere in it -- the 512-byte boot sector loads a 40KB kernel, the kernel works out which display adapter the machine has and switches it into graphics, borrows the video card's own 8x8 character set, and puts up a menu bar.
Everything after that is the interface you remember from a 1984 Macintosh: windows you drag by the title bar with a rubber-band outline, menus you pull down and drag through, a close box and a minimize box, icons for each floppy drive, and a dock along the bottom with one tile per running program. Programs load from a second floppy and run as first-class applications, several at a time.
The whole thing fits in 256K of RAM on an Intel 8086 or 8088 -- the processor in the original IBM PC and PC/XT. It is a hobby project, it is finished enough to use, and the source is 66,183 lines of NASM you can read in an afternoon.
Every figure below comes from the build, not from memory.
Four of the things it is actually good at. There are more on the screenshots page .