ECP
Short for Extended Capabilities Port, a parallel-port standard for PCs that supports bi-directional communication between the PC and attached devices (such as a printer). ECP is about 10 times faster than the older Centronics standard. Another modern parallel port for PCs that offers similar performance is the EPP (Enhanced Parallel Port).

EDO DRAM
Short for Extended Data Output Dynamic Random Access Memory, a type of DRAM that is faster than conventional DRAM. Unlike conventional DRAM which can only access one block of data at a time, EDO DRAM can start fetching the next block of memory at the same time that it sends the previous block to the CPU.

EISA
Acronym for Extended Industry Standard Architecture, a bus architecture designed for PCs using an Intel 80386, 80486, or Pentium microprocessor. EISA buses are 32 bits wide and support multiprocessing.

The EISA bus was designed by nine IBM competitors (sometimes called the Gang of Nine): AST Research, Compaq Computer, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, WYSE, and Zenith Data Systems. They designed the architecture to compete with IBM's own high-speed bus architecture called the Micro Channel architecture (MCA).

The principal difference between EISA and MCA is that EISA is backward compatible with the ISA bus (also called the AT bus), while MCA is not. This means that computers with an EISA bus can use new EISA expansion cards as well as old AT expansion cards. Computers with an MCA bus can use only MCA expansion cards.

EISA and MCA are not compatible with each other. This means that the type of bus in your computer determines which expansion cards you can install.

Neither EISA nor MCA has been very successful. Instead, a new technology called local bus (PCI) is being used in combination with the old ISA bus.

Encryption
A procedure for encoding data that makes it difficult to decode the data without proprietary software of hardware. This procedure protects data or software from unauthorized access or use.

Entropy
The average amount of information represented by a symbol in a message. Entropy is a function of the model used to produce the message and can be reduced by increasing the complexity of the model to better reflect the distribution of source symbols in the original message. Because entropy is a measure of the information contained in a message, it represents the lower bound for compression.

EPP
Short for Enhanced Parallel Port, a parallel port standard for PCs that supports bi-directional communication between the PC and attached devices (such as a printer). EPP is about 10 times faster than the older Centronics standard. Another modern parallel port for PCs that offers similar performance is the ECP (Extended Capabilities Port).

Expanded Memory
Also known as EMS (Expanded Memory Specification), expanded memory is a technique for utilizing more than 1MB (megabyte) 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. There are several versions of EMS. The original versions, called EMS 3.0 and 3.2, enable programs to use an additional 8MB of memory, but for data only. An improved version developed by AST, Quadram and Ashton-Tate is known as EEMS (Extended EMS). EEMS enables programs to use extra memory for code as well as for data. The most recent version of EMS (created in 1987) is known as EMS 4.0 or LIM 4.0, LIM being the initials of the three companies that developed the specification: Lotus, Intel, and Microsoft. EMS 4.0 raises the available amount of memory to 32MB. Until the release of Microsoft Windows 3.0 in 1990, expanded memory was the preferred way to add memory to a PC. The alternative method, called extended memory, was less flexible and could be used only by special programs such as RAM disks. Windows 3.0 and all later versions of Windows, however, contain an extended memory manager that enables programs to use extended memory without interfering with one another. In addition, Windows can simulate expanded memory for those programs that need it (by using the EMM368.EXE driver).

Expansion Bus
A collection of tracks (wires) on a PCB and protocols that allow the expansion of a computer by inserting printed circuit boards (expansion boards). Traditionally, PCs have used an expansion bus called the ISA bus. In recent years, however, the ISA bus has become a bottleneck, so nearly all-new PCs have a PCI bus for performance as well as an ISA bus for backward compatibility.

Expansion Slots
A collection of wires and protocols that allows the expansion of a computer by inserting printed circuit boards (expansion boards). Traditionally, PCs have utilized an expansion bus called the ISA bus. In recent years, however, the ISA bus has become a bottleneck, so nearly all new PCs have a PCI bus for performance as well as an ISA bus for backward compatibility.

Extended Memory
Memory above and beyond the standard 1MB (megabyte) of main memory that DOS supports. Extended memory is only available in PCs with an Intel 80286 or later microprocessor. Two types of memory can be added to a PC to increase memory beyond 1MB: expanded memory and extended memory. Expanded memory conforms to a published standard called EMS that enables DOS programs to take advantage of it. Extended memory, on the other hand, is not configured in any special manner and is therefore unavailable to most DOS programs. However, MS-Windows and OS/2 can use extended memory.