AH = 72h INT 18h Returns: AX = bitmask (FDD count, display type, etc.) BIOS is slow but safe. For games/demos, bypass BIOS and access hardware directly. Common direct I/O ports (simplified): | Port | Purpose | |------|---------| | 0x60 | Keyboard data | | 0x61 | Keyboard control | | 0x66 | Display controller (GDC) | | 0x68 | CRTC address | | 0x6A | CRTC data | | 0xA0 | FDC status | | 0xA1 | FDC data | | 0x30 – 0x3F | Sound (YM2203/2608) | | 0x64 | Timer / interrupt mask |
AH = 24h AL = character (ASCII) BH = color (0–15, 0=black) INT 18h
AH = 29h Returns: AL = current mode Reset disk system
AH = 45h DL = drive Returns: BL = sectors per track, BH = heads Get system timer ticks
AH = 42h (same registers as read)