Expansion board is a printed circuit board that you can insert into a computer to give it added capabilities to core controller boards. It is available to provide a number of different features and capabilities such as data acquisition, a complete user-interface solution, or mass-media storage.

Expanded memory, also known as Expanded Memory Specification(EMS), is a technique for utilizing more than 1MB of main memory in DOS -based computers. The limit of 1MB is built into the DOS operating system. The upper 384K is reserved for special purposes, leaving just 640K of conventional memory for programs.

In computing, an expansion card is a printed circuit board that can be inserted into an expansion slot of a computer motherboard to add additional functionality to a computer system. One edge of the expansion card holds the contacts that fit exactly into the slot. They establish the electrical contact between the electronics (mostly integrated circuits) on the card and on the motherboard.

Expansion slot is the slotlocated inside a computer on the motherboard or riser board that allows additional boards to be connected to it. The maintypes of IBM compatible expansion slots found are ISA, EISA, VESA, PCI, AGP, AMR, and CNR. Expansion slot allows a circuit board to be inserted to add new capabilities to the computer. Nearly all personal computers except portables contain expansion slots for adding more memory, graphics capabilities, and support for special devices. The boards inserted into the expansion slots are called expansion boards, expansion cards, cards, add-ins, and add-ons.

Extended memory refers to memory above the first megabyte of address space in an IBM PC with an 80286 or later processor. Two types of memory can be added to a PC to increase memory beyond 1MB: expanded memory and extended memory. Extended memory is not directly available in real mode, only through EMS, UMB, XMS, or HMA; only applications executing in protected mode can use extended memory directly. In this case, the extended memory is provided by a supervising protected-mode operating system such as Microsoft Windows.

The external bus, also known as expasion bus, is made up of the electronic pathways that connect the different external devices, such as monitor, printer etc, to the computer. These external devices connect to ports on the back of the computer. Those ports are actually part of a small circuit board or 'card' that fits into a connector on your motherboard inside the case. The connector is called an expansion slot. Traditionally, PCs have utilized an expansion bus called the ISA bus. All new PCs have a PCI bus for performance as well as an ISA bus for backward compatibility.

External modem resides in a self-contained box outside the computer system, while an internal modem, which resides on a printed circuit board inserted into the computer. Exernal modem uses COM port to connect to the computer.

An external hard drive is a hard disk placed outside of the computer case. This allows expandability even if a computer's drive bays are full, and also provides an easily removable form of mass storage with very large capacity. A variety of connections are used to connect external hard drives. SCSI and SATA connections are used when the corresponding type of hard drive is inside, with the case containing a simple pass through. USB and Firewire connections require circuitry to convert the hard disk's connection, which is usually IDE, to USB, firewire, or both.

External data bus connects a computer to peripheral devices externally, for example, the Universal Serial Bus (USB) and IEEE 1394.

Extended Backus–Naur form (EBNF) is an extension and simplification of the original Backus–Naur form (BNF) metasyntax notation. Originally developed by Niklaus Wirth, the most commonly used variants of EBNF are currently defined by standards, most notably ISO-14977.