HVAC Control in the New Millennium.pdf - HVAC.Amickracing

Computer Networks and Security 265Chapter 7Computer NetworksAnd SecurityDuring the early days of the computers in the mid-1960s, thecomputer environment consisted of large mainframes withremote terminals connected to the mainframe. These largecomputers required special environmentally controlled computerrooms. Both the computers and the rooms were expensive to buildand required trained personnel for input and output and maintenance.Later, these large computers would grow smaller and some applicationswould be served by minicomputers that did not need special rooms. Theremote terminal system was the main user-computer interface untilaround 1980, when the first personal computers were introduced.The early methods of computing had many disadvantages as wellas some advantages. The computing environment allowed multiple usersto access one computer. These users had access to the same applicationsand files and had some capability of transmitting and receivingmail electronically. Centralized management of the computer was possible.The management of user accounts, files and the hardware wasdone by a group of specialists. The costs of running the cables for theuser terminals were the second most expensive part of the computerinstallation besides the cost of the computer itself.This computing environment was known as centralized computing.If the mainframe or minicomputer went down, all of the users wereaffected and would remain idle until the computer became operational.These breakdowns were common especially where the terminals wereseparated at some distance from the computer. The breakdowns werecostly since the users were unproductive until the computer was operational.The user terminals were known as dumb terminals, since they hadvery little intelligence with most of the host-terminal interface processingdone on the mainframe.©2001 by The Fairmont Press, Inc. All rights reserved.