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

HVAC Control in the New MillenniumMultiple-host connections were possible using a modem to dial upanother computer. This centralized computing environment was usedbecause at the time other alternatives were not available. In 1981 IBMintroduced the personal computer and the computing environment waschanged forever.The personal computer gave the user much more freedom. Thepersonal computer brought the mainframe functionality to the desktop.Initially, it did not bring the power of the mainframe to the desktopsince the early PCs had very little power.PCs became popular because they did away with the disadvantagesof a centralized computer including the cabling costs, environmentallycontrolled rooms and expensive hardware and maintenance costs.The user had control over their computing environment and enjoyedhaving personal application software that would run on individualcomputers. A user could load an application program, enter thedata and print out a report on a local printer much quicker than before.There were no multiple-user applications, messaging capabilities ormultiple-host support.Mainframe-PC connectivity was accomplished using terminalemulation programs that were run on the PC to emulate the terminals.File transfers between the mainframe and the PC were supported withthe terminal emulation software.File transfers were also done using a technique known asSneakernet. Here, a user would save their work on a floppy disk andtake or send the disk to another computer and load it.Shortly after the introduction of the personal computer, the firstlocal area networks (LANs) started to appear. These early LANs alloweda connection in the host-terminal environment and also interconnectionwith the personal computers. Devices and peripherals could be sharedon a single cabling scheme.At first, most LANs were relatively expensive to install and maintain.They started in scientific and engineering applications and spread toalmost all commercial activities. Maintenance costs were also higher withthe early LANs since few people knew how to install and maintain them.The disadvantages of LANs were gradually reduced. Cable costswere reduced and in small and medium-size networks, these cablescould be installed by the user. Networks usually transmit and receive inmegabits per second (Mbps) which is much faster than the 9600 or19,200 bits per second (bps) that the terminal-host interface supported.©2001 by The Fairmont Press, Inc. All rights reserved.