Router
A router is a device that extracts the destination of a packet it receives, selects the best path to that destination,
and forwards data packets to the next device along this path.<1> They connect networks together; a LAN to a WAN for example, to access the Internet. Some units, like the Cisco 1800 (pictured), are available in both wired and wireless models.
ESCON
ESCON (or Enterprise Systems Connection) is an optical serial
interface between IBM mainframe computers and peripheral devices such as storage and tape drives. ESCON is capable of half-duplex communication at a rate of 17 MB/second over distances of up to 43 kilometers. ESCON was introduced by IBM in 1990 to replace the older, slower, copper-based Bus & Tag channel
technology of 1960-1990 era mainframes. The substantially faster FICON channel, which runs over Fibre Channel, is in turn supplanting ESCON.
ESDI
Enhanced Small Disk Interface (ESDI) was a disc interface designed by Maxtor Corporation in the early 1980s to be a follow-on to the ST-506 interface. ESDI improved on ST-506 by moving certain parts that were traditionally kept on the controller (such as the data separator) into the drives themselves, and also generalising the control bus such that more kinds of devices (such as removable disks and tape drives) could be connected. ESDI used the same cabling as ST-506 (one 34-pin common control cable, and a 20-pin data channel cable for each device), and thus could easily be retrofitted to ST-506 applications.
ESDI enjoyed popularity in the mid-to-late 1980s, when SCSI and ATA were young and immature, and ST-506 just wasn''t fast or flexible enough. ESDI could handle data rates of 10, 15, or 20 megabits per second (as opposed to ST-506''s top speed of 7.5 megabits), and many high-end SCSI drives of the era were actually high-end ESDI drives with SCSI bridges integrated on the drive.
By 1990, SCSI had matured enough to handle high data rates and multiple types of drives, and ATA was quickly overtaking ST-506 in the desktop market. These two events made ESDI less and less important over time, and by the mid-1990s, ESDI was no longer in common use