EarthWeb    Click Here!
HomeAccount InfoSubscribeLoginSearchMy ITknowlegeFAQSitemapContact Us
     

ITKnowledge Insider
      
 Read the current newsletter!     
   

  Search Tips
  Advanced Search
   
  

  

Micro House PC Hardware Library Volume II: Network Interface Cards And Modems Micro House PC Hardware Library Volume II: Network Interface Cards And Modems
by Micro House International, Inc. and Scott Mueller
Que, Macmillan Computer Publishing
ISBN: 078971664x   Pub Date: 06/17/98
    Bookmark It

Search this book:
 
Previous Table of Contents Next


Evaluating the Keyboard, Monitor, and Mouse

The keyboard, monitor, and mouse (if any) are usually not significant components on a file server computer, because they receive far less use than their workstation counterparts. Often you can use lower quality, less-expensive components here. A typical file server runs unattended and may go for hours or days without interaction from you. You can power off the monitor for these long periods.


Caution:  
Tuck the server keyboard away so that falling objects (pencils or coffee mugs, for example) do not harm your network’s file server.

Your network server may also have external shared CD-ROM drives, either single or multiple disk and or a network tape drive. If your server has any of these devices, be sure they are easily accessible. When the backup of the server is complete, be sure to remove the tape and store it in a safe place.

Network Interface Cards (NICs)

A network interface card, or NIC, fits into a slot in each workstation and file server. (Some computers now ship with network interface hardware embedded on the motherboard, but most network administrators prefer to select their own.) Your workstation sends requests through the network adapter to the server. The workstation then receives responses through the network adapter when the server delivers all or a portion of a file to that workstation. The sending and receiving of these requests and responses is the LAN equivalent of reading and writing files on your PC’s local hard disk. If you’re like most people, you probably think of reading and writing files in terms of loading or saving your work.

A typical LAN consists of only a single data channel connecting its various computers. This is called a baseband network. As a result of this, only two network adapters can communicate with each other at the same time. If one person’s workstation is currently accessing the file server (processing the requests and responses that deliver a file to the workstation), then other users’ workstations must wait their turn. Fortunately, such delays are usually not noticeable. The LAN gives the appearance of many workstations accessing the file server simultaneously.

Ethernet adapters have a single BNC connector (for Thinnet), a D-shaped 15-pin connector called a DB15 (for Thicknet), a connector that looks like a large telephone jack called an RJ45 (for 10BaseT), or sometimes a combination of all three. Token Ring adapters can have a 9-pin connector called a DB9 or sometimes an RJ45 telephone jack outlet. Figure 1-3 shows a high-performance Token Ring adapter with both kinds of connectors.


FIG. 1-3  The Thomas-Conrad 16/4 Token Ring adapter (with a 9-pin connector and a telephone wire connector).

Cards with two or more connectors enable you to choose from a wider variety of LAN cables. A Token Ring card with two connectors, for example, enables you to use shielded twisted pair (STP) or unshielded twisted pair (UTP) cable. You cannot use both connectors at the same time, however, except on special adapters designed specifically for this purpose.

Shielded versus Unshielded Twisted Pair

When cabling was being developed for use with computers, it was first thought that shielding the cable from external interference was the best way to reduce interference and allow for greater transmission speeds. However, it was discovered that twisting the pairs of wires is a more effective way to prevent interference from disrupting transmissions. As a result, earlier cabling scenarios relied on shielded cables rather than the unshielded cables more commonly in use today.

Shielded cables also have some special grounding concerns because one—and only one—end of a shielded cable should be connected to an earth ground; issues arose where people inadvertently caused grounding loops to occur by connecting both ends, or caused the shield to act as an antenna because it wasn’t grounded.

Grounding loops are situations where two different grounds are tied together. This is a bad situation because each ground can have a slightly different potential. This results in a circuit that has very low voltage but infinite amperage. This causes undue stress on electrical components and can be a fire hazard.

The LAN adapter card in your PC receives all the traffic going by on the network cable, accepts only the messages destined for your workstation, and passes on the rest to the next machine. The adapter hands these messages over to your workstation when the workstation is ready to attend to them. When the workstation wants to send a request to a server, the adapter card waits for the appropriate time (according to the network type), and inserts your message into the data stream. The workstation is also notified as to whether the message arrived intact, and resends the message if it was garbled.


Previous Table of Contents Next

HomeAccount InfoSubscribeLoginSearchMy ITKnowledgeFAQSitemapContact Us
Products |  Contact Us |  About Us |  Privacy  |  Ad Info  |  Home

Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 EarthWeb Inc. All rights reserved. Reproduction whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Read EarthWeb's privacy statement.