Editing Parallel port (section)

==Historical uses==
[[Image:HP C4381A CD-Writer Plus 7200 Series-4077.jpg|right|thumb|''[[Hewlett-Packard|HP]] C4381A CD-Writer Plus 7200 Series'', showing parallel ports to connect between a printer and the computer.]]
Before the advent of [[USB]], the parallel interface was adapted to access a number of peripheral devices other than printers. One early use of the parallel port was for [[dongle]]s used as hardware keys which were supplied with application software as a form of software copy protection. Other uses included [[optical disc drive]]s such as [[Compact disc|CD]] readers and writers, [[Zip drive]]s, [[Image scanner|scanners]], [[tape drives]],<ref>{{cite book|title=Handbook of Computer Troubleshooting|author=Michael Byrd|isbn=978-1888998993|year=2013|publisher=UNKNO }}</ref> external [[modem]]s, [[gamepad]]s, and [[joystick]]s. Some of the earliest portable [[MP3 player]]s required a parallel port connection for transferring songs to the device.<ref>{{cite web
 |url         = http://www.targetpc.com/hardware/audio/mp3/dlink_dmp100/index2.shtml
 |title       = The D-Link DMP-100 MP3 Player
 |page        = 2
 |last        = Mitskaniouk
 |first       = Oleg
 |date        = 2000-06-19
 |publisher   = Target PC Magazine
 |access-date  = 2012-07-20
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20150501140844/http://www.targetpc.com/hardware/audio/mp3/dlink_dmp100/index2.shtml
 |archive-date = 2015-05-01
}}</ref> Adapters were available to run [[SCSI]] devices via parallel.  Other devices such as [[EPROM]] programmers and hardware controllers could be connected via the parallel port.

===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.

===Access===
DOS-based systems make the logical parallel ports detected by the BIOS available under device names such as ''LPT1'',  ''LPT2'' or ''LPT3'' (corresponding with logical parallel port 1, 2, and 3, respectively). These names derive from terms like '''Line Print Terminal''', '''Local Print Terminal''' (both abbreviated as '''LPT'''), or Line Printer. A similar naming convention was used on [[Incompatible Timesharing System|ITS]], [[Digital Equipment Corporation|DEC]] systems, as well as in [[CP/M]] and [[86-DOS]] (''LST'').

In [[DOS]], the parallel printers could be accessed directly on the [[command line]]. For example, the command "<code>TYPE C:\AUTOEXEC.BAT &gt; LPT1:</code>" would redirect the contents of the [[AUTOEXEC.BAT]] file to the printer port. A '''PRN''' device was also available as an alias for LPT1. Some operating systems (like [[Multiuser DOS]]) allow to change this fixed assignment by different means. Some DOS versions use resident driver extensions provided by MODE, or users can change the mapping internally via a [[CONFIG.SYS]] [[PRN (CONFIG.SYS directive)|PRN]]=n directive (as under DR-DOS 7.02 and higher). [[DR-DOS]] 7.02 also provides optional built-in support for ''LPT4'' if the underlying BIOS supports it.

PRN, along with CON, AUX and a few others are invalid file and directory names in DOS and Windows, even on [[Windows XP]] and later. This set of invalid file and directory names also affects [[Windows 95]] and [[Windows 98|98]], which had an [[MS-DOS]] device in path name vulnerability in which it causes the computer to crash if the user types "C:\CON\CON", "C:\PRN\PRN" or "C:\AUX\AUX" in the Windows Explorer address bar or via the Run command.{{citation needed|date=May 2013}} [[Microsoft]] has since released a patch to fix this issue, however new installations of Windows 95 and 98 are not patched with this fix and will still have this issue.

A special "<code>PRINT</code>" command also existed to achieve the same effect. [[Microsoft Windows]] still refers to the ports in this manner in many cases, though this is often fairly hidden.

In [[SCO UNIX]] and [[Linux]], the first parallel port is available via the filesystem as <code>/dev/lp0</code>. Linux IDE devices can use a ''paride'' (parallel port IDE) driver.<ref>
{{cite book
| last1                 = Barkakati
| first1                = Naba
| title                 = Linux All-in-One Desk Reference For Dummies
| url                   = https://books.google.com/books?id=1BPAJhqtsQwC
| edition               = 2
| publisher             = John Wiley & Sons
| date      = 2006
| page                  = 482
| isbn                  = 9780471793137
| access-date            = 2015-09-11
| quote                 = Some IDE devices use a parallel port IDE adapter — that's what the PARIDE option refers to.
}}
</ref>