Editing Null modem (section)

== Applications ==
The original application of a null modem was to connect two teleprinter terminals directly without using modems. As the RS-232 standard was adopted by other types of equipment, designers needed to decide whether their devices would have DTE-like or DCE-like interfaces. When an application required that two DTEs (or two DCEs) needed to communicate with each other, then a null modem was necessary.<ref>{{cite web |url=http://adtpro.sourceforge.net/connectionsserial.html |title=ADTPro - ADTPro Serial Cabling |publisher=sourceforge.net |date=2011-01-25 |access-date=2013-12-26}}</ref>

Null modems were commonly used for [[file transfer]] between computers, or remote operation. Under the [[Microsoft Windows]] [[operating system]], the [[direct cable connection]] can be used over a null modem connection. The later versions of [[MS-DOS]] were shipped with the [[Interlnk|InterLnk]] program. Both pieces of software allow the mapping of a [[hard disk]] on one computer as a network drive on the other computer. No Ethernet hardware (such as a [[network interface card]] or a modem) is required for this.<ref>{{cite web |url=https://www.angelfire.com/ma/mantasdos/interlnk.html |title=MS-DOS External commands - INTERLNK |publisher=[[Angelfire]] |access-date=2013-12-26}}</ref> On the [[Amiga]] computer, a null modem connection was a common way of [[:Category:Multiplayer null modem games|playing multiplayer games]] between two machines.

The popularity and availability of faster information exchange systems such as [[Ethernet]] made the use of null modem cables less common. In modern systems, such a cable can still be useful for [[Kernel (operating system)|kernel]] mode development, since it allows the user to remotely debug a kernel with a minimum of device drivers and code (a serial driver mainly consists of two [[FIFO (computing and electronics)|FIFO]] buffers and an [[interrupt service routine]]). [[KGDB]] for [[Linux]], ddb for [[Berkeley Software Distribution|BSD]], and [[WinDbg|WinDbg or KD]] for Windows can be used to remotely debug systems, for example. This can also provide a serial console through which the in-kernel debugger can be dropped to in case of kernel panics, in which case the local monitor and keyboard may not be usable anymore (the [[GUI]] reserves those resources and dropping to the debugger in the case of a panic won't free them).

Another context where these cables can be useful is when administering "headless" devices providing a serial administration console (i.e. managed switches, rackmount server units, and various embedded systems). An example of embedded systems that widely use null modems for remote monitoring include [[Remote Terminal Unit|RTUs]], device controllers, and smart sensing devices. These devices tend to reside in close proximity and lend themselves to short run serial communication through protocols such as [[DNP3]], [[Modbus]], and other IEC variants. The Electric, Oil, Gas, and Water Utilities are slow to respond to newer networking technologies which may be due to large investments in capital equipment that has useful service life measured in decades. Serial ports and null modem cables are still widely used in these industries with Ethernet just slowly becoming a widely available option.