| ECP |
| See IEEE 1284. |
| EEPROM |
| (Electrically Erasable
Programmable ROM) A rewritable memory chip that holds
its content without power. EEPROMs have a lifespan of between 10K
and 100K write cycles, which is considerably greater than the E-PROMs
(dash inserted for easier comparison) that came before them. Unlike E-PROMs, which have to be placed under UV light for erasure, EEPROMs are erased in place. They use a floating gate to hold a charge like an E-PROM and have a second transistor for erasure. For programming, early EEPROMs were like E-PROMs. They were generally programmed outside of the system because they needed a higher 12v to charge the gate. Subsequent EEPROMs used the same voltage as the chip and were programmed in place. See EPROM, memory types and flash memory. |
| Enhanced keyboard |
| A 101-key keyboard from IBM that superseded the PC and AT keyboards. It is the type commonly used on PCs today. |
| enhanced parallel port |
| See EPP. |
| EPP |
| (1) (Enhanced Parallel Port)
See IEEE 1284. (2) (Ethernet Packet Processor) A chip from Kalpana, Inc., Santa Clara, CA that doubles speed of Ethernet transmission to 20Mbits/sec. In 1994, Kalpana was acquired by Cisco. |
| EPP/ECP |
| See IEEE 1284. |
| EPROM |
| (Erasable Programmable
ROM) A rewritable memory chip that holds its content without
power. Having a lifespan of only a few hundred write cycles, EPROM
chips are programmed in a separate device before being placed on the
circuit board, and they are removed for reprogramming. EPROMs use a transistor with a floating gate underneath the control gate that holds a charge for more than a decade. To write the bit, a high voltage is applied to the control gate. For erasure, the chip is removed from the board and placed under intense ultraviolet (UV) light for approximately 20 minutes. Although still used, EPROMS evolved into EEPROMs and flash memory, both of which can be electrically erased in place. See memory types.  |
| Ethernet | |||
| The most widely used
local area network (LAN) access method, defined by the IEEE as the
802.3 standard. Ethernet has become so popular that a specification for "LAN
connection" or "network card" generally implies Ethernet without saying so.
All Macs and many PCs come with 10/100 Ethernet ports for home use, not just to create a
small home network, but to connect to the Internet via a DSL or
cable modem, which requires it. A 10/100 port means that it supports both 10BaseT at 10
megabits per second (Mbps) and 100BaseT at 100 Mbps. Ethernet is normally a shared media LAN. All stations on the segment share the total bandwidth, which is either 10 Mbps (Ethernet), 100 Mbps (Fast Ethernet) or 1000 Mbps (Gigabit Ethernet). With switched Ethernet, each sender and receiver pair have the full bandwidth. Twisted pair Ethernet (10BaseT) uses economical telephone wiring and standard RJ-45 connectors, often taking advantage of installed wires in a building. It is wired in a star configuration and requires a hub or switch. Fast Ethernet (100BaseT) is similar, but uses two different twisted pair configurations (see 100BaseT). Today's Ethernet network adapters, hubs and switches generally support both 10BaseT and 100BaseT (10/100) and automatically sense and adapt to the transmitted speed. The earlier versions of 10 Mbps Ethernet used coaxial cable (see 10Base5 and 10Base2). Fiber-optic Ethernet (10BaseF and 100BaseFX) is impervious to external radiation and is often used to extend Ethernet segments up to 1.2 miles. Specifications exist for complete fiber-optic networks as well as backbone implementations. FOIRL (Fiber-Optic Inter Repeater Link) was an earlier standard that is limited to .6 miles distance. Ethernet transmits variable length frames from 72 to 1518 bytes in length, each containing a header with the addresses of the source and destination stations and a trailer that contains error correction data. Higher-level protocols, such as IP and IPX, fragment long messages into the frame size required by the Ethernet network being employed (see MTU). Ethernet uses the CSMA/CD technology to broadcast each frame onto the physical medium (wire, fiber, etc.). All stations attached to the Ethernet are "listening," and the station with the matching destination address accepts the frame and checks for errors. Ethernet is a data link protocol (MAC layer protocol) and functions at layers 1 and 2 of the OSI model. Ethernet was invented by Robert Metcalfe and David Boggs at Xerox PARC in 1973, which first ran at 2.94 Mbps. Metcalfe later joined Digital where he facilitated a joint venture between Digital, Intel and Xerox to collaborate further on Ethernet. Version 1 was finalized in 1980, and products shipped in the following year. In 1983, the IEEE approved the Ethernet 802.3 standard. See 100BaseT, Gigabit Ethernet, 10 Gigabit Ethernet and switched Ethernet. . |
|||
10 Mbps AND 100 Mbps ETHERNET LIMITATIONS |
|||
| Type | Maximum Segment length |
Maximum Devices |
|
| TWISTED
PAIR (star topology) |
|||
| 10BaseT | 328 ft. (100 m) | 1 | |
| 100BaseT | 328 ft. (100 m) | 1 | |
| COAX
(bus topology) |
|||
| 10Base5 "thick" | 1640 ft. (500 m) | 100 | |
| 10Base2 "thin" | 607 ft. (185 m) | 30 | |
| FIBER
(star topology) |
|||
| FOIRL | .6 mi. (1 km) | 1 | |
| 10BaseF | 1.2 mi. (2 km) | 1 | |
| 100BaseFX multimode | 1.2 mi. (2 km) | 1 | |
| 100BaseFX single-mode | 6 mi. (10 km) | 1 | |