Glossary

INT 13h

The BIOS disk interrupt used by boot code before the DOS filesystem is available.

BIOS

Firmware services available before DOS exists; it loads the boot sector and provides interrupts such as INT 13h disk I/O.

IVT

The table at physical address zero containing 256 far pointers for CPU, BIOS, and DOS interrupts.

real mode

The original 8086-compatible CPU mode where addresses are segment:offset and there is no memory protection.

SAHF

An x86 instruction that loads status flags from AH; Ascendancy exposed a QEMU TCG parity-flag bug here.

TCG

QEMU's Tiny Code Generator CPU backend, used when running guests without hardware virtualization.

x87

The x86 floating-point instruction set. DOS extenders and games may exercise it heavily after startup.

COM1

The first PC serial port. LainDOS uses it as the primary machine-readable debug log.

monitor socket

A QEMU control channel used to send keys, capture screenshots, inspect registers, or quit scripted runs.

serial log

Captured COM1 text output, used by tests to detect PASS, FAIL, exceptions, and unhandled DOS calls.

CHS

Cylinder/head/sector disk addressing used by old BIOS INT 13h calls; it has stricter size limits than LBA.

QEMU FAT export

QEMU's file=fat:rw drive mode, which exposes a host directory as a DOS FAT drive for quick real-DOS comparisons.

DOS API

The program-facing DOS service contract, mostly reached through INT 21h in LainDOS.

DTA

The DOS buffer where FindFirst/FindNext and some FCB calls return directory search results.

INT 21h

The main DOS API interrupt. Programs select services such as open, read, EXEC, and exit with AH.

86Box

A PC emulator used here as a period-hardware comparison target when QEMU behavior looks suspicious.

Bochs

A debugger-friendly x86 emulator useful as a third opinion when QEMU and 86Box disagree.

QEMU

The default fast emulator for automated LainDOS builds, tests, monitor probes, and game smoke runs.

real DOS

A comparison run using MS-DOS, PC DOS, or FreeDOS instead of LainDOS to separate guest bugs from emulator bugs.

v86

A browser-hosted x86 emulator used by the site to boot the small LainDOS demo image.

VNC

A remote framebuffer protocol QEMU can expose so tests and humans can inspect graphical output headlessly.

BPB

The FAT boot-sector table that describes sector size, FAT location, root directory size, and cluster layout.

FAT12

The 12-bit FAT format used by 1.44 MB floppy images and the early LainDOS boot path.

FAT16

The 16-bit FAT format LainDOS uses for larger hard-disk style images.

PIC

The Programmable Interrupt Controller that masks and dispatches hardware IRQs such as keyboard IRQ1.

PIT

The Programmable Interval Timer that drives the classic PC timer tick and many game timing loops.

EMS

Expanded Memory Specification: bank-switched memory exposed through an EMS page frame.

MCB

A 16-byte DOS memory header that describes the allocated or free block immediately after it.

XMS

Extended Memory Specification services for memory above 1 MiB, used by many later DOS games and extenders.

INT 33h

The conventional DOS mouse-driver interrupt implemented by LainDOS for game input.

DOS/4GW

A DOS extender that switches games into protected mode while still using DOS for startup and file services.

DPMI

DOS Protected Mode Interface, the service layer many protected-mode DOS programs expect from an extender or host.

MZ

The DOS EXE header signature. LainDOS uses it to distinguish EXE files from flat COM programs.

PSP

The DOS data block placed before each program, holding terminate vectors, the job file table, command tail, and environment pointer.

AdLib

The classic Yamaha OPL FM-synthesis sound path. QEMU exposes it with -device adlib, separately from -device sb16; attach it only for games that need that probe path.

SB16

Sound Blaster 16 audio hardware. QEMU exposes the DSP path with -device sb16; some games also need the separate -device adlib OPL path.

NASM

Netwide Assembler, the assembler used for LainDOS boot, kernel, shell, and focused test programs.

smoke test

A coarse end-to-end run that proves a game or workflow reaches a visible expected state without fatal markers.

framebuffer

The raw pixels currently shown by VGA; smoke tests hash or inspect it when serial output cannot prove gameplay.

retrace

The VGA vertical-blank signal that many games poll through port 0x3DA for timing.

VGA

The PC video standard LainDOS and the demos use for text and graphics output.