COM (hardware interface)

COM (Communication port) is the original, yet still common, name of the serial port interface on IBM PC-compatible computers. It might refer not only to physical ports, but also to virtual ports, such as ports created by Bluetooth or USB-to-serial adapters.

History

Most PC-compatible computers in the 1980s and 1990s had one or two COM ports. As of 2007, most computers ship with one or no physical COM ports. As of 2014, most PC-compatible computers don't include any COM ports. A lot of them do still include a COM header.

After the RS-232 COM port was removed from most IBM PC compatible computers in the 2000s, an external USB-to-UART serial adapter cable was used to compensate for the loss. A major supplier of these chips is FTDI. ....

I/O addresses

The COM ports are interfaced by an integrated circuit such as 16550 UART. This IC has seven internal 8-bit registers which hold information and configuration data about which data is to be sent or was received, the baud rate, interrupt configuration and more. In the case of COM1, these registers can be accessed by writing to or reading from the I/O addresses 0x3F8 to 0x3FF.

DOS

DOS /dɒs/, short for disk operating system, is an acronym for several computer operating systems that were operated by using the command line.

MS-DOS dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 including the partially MS-DOS-based Microsoft Windows (95, 98, and Millennium Edition). "DOS" is used to describe the family of several very similar command-line systems, including MS-DOS, PC DOS, DR-DOS, FreeDOS, ROM-DOS, and PTS-DOS.

In spite of the common usage, none of these systems were simply named "DOS" (a name given only to an unrelated IBM mainframe operating system in the 1960s). A number of unrelated, non-x86 microcomputer disk operating systems had "DOS" in their names, and are often referred to simply as "DOS" when discussing machines that use them (e.g. AmigaDOS, AMSDOS, ANDOS, Apple DOS, Atari DOS, Commodore DOS, CSI-DOS, ProDOS, and TRSDOS). While providing many of the same operating system functions for their respective computer systems, programs running under any one of these operating systems would not run under others.

CONFIG.SYS

CONFIG.SYS is the primary configuration file for the DOS and OS/2 operating systems. It is a special ASCII text file that contains user-accessible setup or configuration directives evaluated by the operating system during boot. CONFIG.SYS was introduced with DOS 2.0.

Usage

The directives in this file configure DOS for use with devices and applications in the system. The CONFIG.SYS directives also set up the memory managers in the system. After processing the CONFIG.SYS file, DOS proceeds to load and execute the command shell specified in the SHELL line of CONFIG.SYS, or COMMAND.COM if there is no such line. The command shell in turn is responsible for processing the AUTOEXEC.BAT file.

CONFIG.SYS is composed mostly of name=value directives which look like variable assignments. In fact, these will either define some tunable parameters often resulting in reservation of memory, or load files, mostly device drivers and TSRs, into memory.

In DOS, CONFIG.SYS is located in the root directory of the drive from which the system was booted.