Editing Parallel port (section)

===Interfaces===
Most PC-compatible systems in the 1980s and 1990s had one to three ports, with communication interfaces defined like this:

*Logical parallel port 1: [[Memory-mapped I/O|I/O port]] 0x3BC, [[Interrupt request (PC architecture)|IRQ]] 7 (usually in monochrome graphics adapters)
*Logical parallel port 2: I/O port 0x378, IRQ 7 (dedicated IO cards or using a controller built into the mainboard)
*Logical parallel port 3: I/O port 0x278, IRQ 5 (dedicated IO cards or using a controller built into the mainboard)

If no printer port is present at 0x3BC, the second port in the row (0x378) becomes logical parallel port 1 and 0x278 becomes logical parallel port 2 for the BIOS. Sometimes, printer ports are jumpered to share an interrupt despite having their own IO addresses (i.e. only one can be used interrupt-driven at a time). In some cases, the BIOS supports a fourth printer port as well, but the base address for it differs significantly between vendors. Since the reserved entry for a fourth logical printer port in the [[BIOS Data Area]] (BDA) is shared with other uses on PS/2 machines and with S3 compatible graphics cards, it typically requires special drivers in most environments.
Under DR-DOS 7.02 the BIOS port assignments can be changed and overridden using the [[LPT1 (CONFIG.SYS directive)|LPT1]], [[LPT2 (CONFIG.SYS directive)|LPT2]], [[LPT3 (CONFIG.SYS directive)|LPT3]] (and optionally [[LPT4 (CONFIG.SYS directive)|LPT4]]) [[CONFIG.SYS]] directives.