bi-directional interface designed to allow devices like printers, scanners, or storage devices to transmit large amounts of data while quickly being able to switch channel direction. EPP can provide up to 2 MByte/s bandwidth, approximately 15 times the speed achieved with normal parallel-port communication with far less CPU overhead. Extended Capability Port (ECP) is a half-duplex bi-directional interface similar to EPP, except that PC implementations use direct memory access (usually ISA DMA on channel 3) to provide even faster data transfer than EPP by having the ISA DMA hardware and the parallel port interface hardware handle the work of transferring the data instead of letting the CPU do this work. Many devices that interface using this mode support RLE compression. ECP can provide up to 2.5 MByte/s of bandwidth, which is the natural limit of 8-bit ISA DMA. An ECP interface on a PC can improve transfers to pre-IEEE-1284 printers as well, by reducing the CPU load during the transfer; however, the transfer in that case is unidirectional. Most recent computers that include a parallel port can operate the port in ECP or EPP mode, or both simultaneously. IEEE-1284 requires that bi-directional device communication is always initiated in Nibble Mode. If the host receives no reply in this mode, it will assume that the device is a legacy printer, and enter Compatibility Mode. Otherwise, the best mode that is supported on both sides of the connection is negotiated between the host and client devices by exchanging standardized Nibble Mode messages. IEEE 1284 connectors and cables An IEEE-compliant cable must meet several standards of wiring and quality. Three types of connectors are defined: Type A: DB-25 25 pin, for the host connection. Type B: Centronics (officially called "Micro Ribbon") 36-pin, for the printer or device connection. Type C: Mini-Centronics (MDR36 or HPCN36) 36-pin, a half-pitch, smaller alternative for the device connection that has not proven popular. There are two kinds of IEEE 1284 cables: IEEE 1284-I: uses IEEE 1284-A and IEEE 1284-B connectors. IEEE 1284-II: uses IEEE 1284-C connectors. In IEEE 1284 Daisy Chain Specification, up to eight devices can be connected to a single parallel port. All modes use TTL voltage logic levels, which limits the possible cable length to a few meters unless expensive special cables are used. For detailed specifications, including pinouts, refer to the links below. IEEE 1284 standards IEEE 1284-2000: Standard Signaling Method for a Bi-directional