Chapter 5

LAN Hardware


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Chapter 8 | Chapter 9 | Chapter 10 | Chapter 11 | Chapter 12 | Chapter 13 | Chapter 14 | Chapter 15


Summary 

Chapter 5 is about LAN hardware.  The main focus is server hardware.  When picking a server their are many things to consider.  You have to decide the amount and type of RAM, the size, interface, and number of a hard drives.   You also have to think about what type of processor and how fast you want it.  You must make sure that all the devices you pick will work with each other.  And you have to make sure that the server will be powerful enough to fit your needs. One option is to purchase a pre-configured server from a hardware manufacturer such as IBM or Dell.  This is usually a good idea because you will get a warranty with this system.  Another option is to build the server yourself by buying all the components and putting them together.


Server Platforms

What is a server?  What is it used for?  Below is a list of common task that a server can perform.  Remember that you don't need one server for each task, one server can perform multiple functions.

  • File Service/Server - People will store files on the server.  When a person opens a file that is on a file server the server will transmit the file through the network to the destination PC.  The file will load into the PC's  memory as the person works on it.  Once the person is done with the file it is copied back to the server.  This type of setup will not work with a database, you don't want a large database copied over the network every time you open it. 

  • Database Server - In this setup a database is stored on a server.  All data processing is done server side.  So when someone opens a database the data isn't copied to their PC. When they make a change it is sent to the server.  We will learn in Chapter 8 what happens on the server side of this transaction.

  • Print Services - A server with print services will store the print queue.  When a client send a print to the printer it will be sent to the server and placed in a queue waiting for its turn at the printer.  We will be covering more on printing in Chapter 7.  This is not to be confused with a print server which is used to make a printer a network printer.

  • Application Services - This will be covered in Chapter 8


Server Selection Criteria

  • LAN Operating System Requirements - When selecting a server you want to make sure it's powerful enough to handle the network operating systems you choose.  Below is a table that shows different OS's and their minimum and recommended requirements.   With processor speeds over 3Ghz and memory over 1GB we can see that it is easy to pass most of these requirements. 
Operating System Minimum Processor Minimum Memory Recommended Processor Recommended Memory
Windows 95 386 DX 4MB 486SX-25 8MB
Windows 98 486 DX 16MB / 24MB SE Pentium 24MB
Windows NT4 486 DX 12MB Pentium 32MB
Windows 2000 Pentium 133 32MB Pentium II 64MB
Windows XP Pentium 233 64MB Pentium II 300 128MB
Novell 6 Pentium II 256MB Pentium III 700 512MB

 

  • Server Disk Drives - There are many things to consider when choosing a hard drive for a server.  The interface, the speed, the size etc...

  • How does a hard drive work? Inside a hard drive are platters stacked on top of each other.  An arm which contains a read/write head goes between each one .  As the drive spins the arms moves back and forth an information is either written or read from the platters.  The drive is broken down into Cylinders, Tracks and Sectors which assist in the addressing.  The outer portion of the drive spins the fastest.

Hard Drive Layout

(Click to enlarge)

  • Hard Drive Interfaces:
    • IDE (Integrated Drive Electronics) IDE is most commonly used in client PC's.  This interface has improved a lot over the years.  Initially it just supported hard drive in ATA (Advanced Technology Attachment) mode.  With the addition of a Packet Interface (ATAPI) CD-Roms and other devices were supported.  IDE is in the progress of a major overhaul.  Currently an IDE cable is a parallel setup where data travels on 40 wires at a current maximum speed of 133Mbps.  The new Serial IDE has 7 wires and a starting speed of 150Mbps.
    • SCSI (Small Computer System Interface) - SCSI (Scuzzy) is most commonly used in servers.  SCSI Hard drive spin faster then IDE (Max of 15,000 rpm compared to 7200 rpm on IDE)  Currently SCSI can transfer at 320Mbps.  SCSI hard drives can be hot swappable* and be configured in a RAID* configuration (RAID is covered in Chapter 7) * Serial IDE supports hot swapping, and IDE has supported RAID for the past several years.
  • Memory -

    • L1 Cache (pronounced Cash) is a very small amount of static memory stored on the CPU (Central Processing Unit) usually between 16Kb - 256Kb

    • L2 Cache is a slightly larger and slower then L1 Cache and is stored on the motherboard. Usually 512Kb -2048Kb Sometimes this is found on a COAST (Cache On A STick)

    • RAM - Random Access Memory is a lot bigger and slower then L2 Cache.  This is usually on a SIMM or DIMM that plugs into the motherboard. Memory usually ranges from 128MB to 4096MB

      • SIMM is defined as Single Inline Memory Module.  DIMM is a Dual Inline Memory Module.  The difference between the two is that SIMMs use both sides of each contact together. Each contact gives a single signal.  DIMMs, on the other hand, use the opposite sides of each contact for separate signals.  A server will usually use DIMMs with ECC (error-correcting code). 

 

 

 

Different Types of memory.

(Click to enlarge)

  • Virtual Memory - Very very very slow.  This is using the hard drive as RAM when you run out of RAM. 
  • CPU - The type of CPU you choose for your server is important.  The CPU is the main brain of the computer.  When a program is started a process is created.  A process is made up of one or more threads.  A thread is a set of commands that a processor executes.  You can add a second processor to help execute these threads.  There are two modes that a multiprocessor PC will run, symmetric and asymmetric.  With symmetric multiprocessing the processors execute any thread that is available, asymmetric each processor is dedicated to a specific task.  For example one processor could be dedicated to system threads and another to application threads.  With this option you could end up with one processor idle and one busy.  Symmetric is the preferred option.  It is important to note that if you have two processors you will not have twice the speed.  Their are some processor cycles lost by each CPU trying to keep track of the other CPU. Each processor shares memory so one CPU may have to wait  for the other CPU to update a section on RAM.


  • Buses - We discussed some of the buses that a computer uses. The purpose of a bus is to allow for expansion.  The Northbridge and Southbridge chips act as hubs for the different Busses

    • IDE - Integrated Drive Electronics

    • ISA - Industry Standard Architecture

    • PCI - Peripheral Component Interconnect

    • AGP - Accelerated Graphics Port

    • USB - Uneversal Serial Bus

    • PS2 - Personal System 2

    • CMOS - Complementary Metal Oxide Semiconductor

    • LPT - Local Printer Terminal

    • COM - Communications Port

 A Diagram of a motherboard (Abit KT7a-RAID)

(Click to enlarge)


Uninterruptible Power Supply

A UPS or Uninterruptible Power Supply is a device that sits between a power supply (e.g. a wall outlet) and a device (e.g. a computer) to prevent undesired features of the power source (outages, sags, surges, bad harmonics, etc.) from the supply from adversely affecting the performance of the device.

A UPS has internal batteries to guarantee that continuous power is provided to the equipment even if the power supply stops providing power. Of course the UPS can provide power for a while, typically a few minutes, but that is often enough to ride out power company glitches or short outages. Advantages:

  1. Computer jobs don't stop because the power fails.
  2. Users not inconvenienced by computer shutting down.
  3. Equipment does not incur the stress of another (hard) power cycle.
  4. Data isn't lost because a machine shut down without doing a "sync" or equivalent to flush cached or real time data

UPS FAQ


Hubs and Switches

A hub is a multi-port repeater. It simply passes on (repeats) all the information it receives, so that all devices connected to its ports receive that information.  This can result in a lot of unnecessary traffic being sent to all devices on the network.  Hubs pass on traffic to the network regardless of the intended destination.  This is where a switch comes in, switches control the flow of network traffic based on the address information in each packet. A switch learns which devices are connected to its ports and then forwards the packets to the appropriate port only. This allows simultaneous communication across the switch.  This will be covered in more detail in Chapter 14.  Below is a picture that shows what happens when two computers send data at the same time and a switch is involved.  You can see that a collision is avoided.  Click on the picture to see the full image.

 

 

 

 

 

 

 

 

A switch on a network preventing collisions

(Click to enlarge)


More Information

 

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