Speaking Notes

PADM

January 28, 2010

Dr. Neubauer

 

WHERE WE ARE

 

 

Chapter 2 of Barrett and Greene

 

Technology is not the solution to every problem and there is no "one size fits all."  One works on one situation or place may not work in other places.

 

Moore's Law is that computing technology gets about twice as good every 18 months and the price is fairly constant.  This has serious implications for public agencies given the nature of public budgetary processes.

 

Citizens generally want news ways to do things but they don't want to give up the old delivery systems.  This limits the ability to cut costs by "going digital."  Agencies wind up running parallel systems.

 

Applying for jobs is increasingly online, in both public and private sectors.

 

When building a new system it is very important to involve kinds of people who will use the new system.  A lot of money is wasted by assuming to know what real "end users" want.  Their buy-in is a critical success factor.

 

Software like Techsmith Morae can be used to improve software interfaces by better understanding how users experience the software application.  This is the kind of software used for end-user USABILITY TESTING.  Good software applications . . .

 

 

 

 

Chapter 2 of the Stair and Reynolds book.

 

WHY STUDY HARDWARE?

 

PHERIPHERALS

 

 

THE CASE ITSELF

 

POWER SUPPLY

 

MOTHERBOARD

 

 

 

CPU (central processing unit)

 

RAM (random access memory)

 

BUS

 

CARDS

 

PORTS

 

ROM (read only memory)

 

CMOS

 

SOME ADDITIONAL MATERIAL:

 

The "evolution" from centralized computing to networks.

 

In the early days big organizations had one big mainframe computer and it did everything in batch mode.

Card readers were eventually replaced by "dumb terminals."

When microcomputers became available some people began substituting microcomputers for dumb terminals.

Suddenly you had a highly centralized network and a very early form of CLIENT-SERVER computing!

 

Organizations began to realize that by NETWORKING small computers they could avoid the cost of a mainframe computer.

 

In a PEER-TO-PEER network all the computers are similar and they just have the ability to share data with one another.

In a CLIENT-SERVER network some of the computers have SPECIALIZED FUNCTIONS, such as the computer that is attached to the printer.

 

This is good for organizations in multiple ways.  DONE PROPERLY YOU DON'T HAVE TO PAY FOR SO MANY LICENSES AND CAN STILL BE LEGAL.  Use an APPLICATION SERVER to achieve this.

 

Three basic "kinds" of networks in organizations.

 

 

How are the computers on a LAN likely to be "connected" to one another?

How are the computers on a MAN likely to be "connected" to one another?

How are the computers on a WAN likely to be "connected" to one another?

 

Regarding a WAN, what is the alternative to some kind of dedicated connection?

 

Three different LAN topologies.

 

BUS – everything directly connected to one wire or one frequency.

STAR – everything directly connect to one special device "in the middle"

RING – basically a bus with the ends connected and the packets (frames) all go around in the same direction

 

The problem with a BUS topology is COLLISIONS.  This kind of network does not SCALE well.

The problem with a STAR topology is that if you lose the thing in the middle nothing connects to anything else.

A RING topology SCALES fairly well but if it gets cut, all connectivity is lost.

 

The notion of the ability of a networked application to SCALE is very important.  As you add more people (or automated parts) using the application at the same time PERFORMANCE tends to decrease.  The application SCALES WELL to the point that adding more users causes it to slow down so much that performance is not acceptable.

 

Applications (especially those having read/write access to a DATABASE) must accommodate CONCURRENCY.  This involves locking down parts of the database temporarily to prevent CONCURRENCY ERRORS.  NO TWO USERS SHOULD HAVE "WRITE" ACCESS TO THE SAME PART OF THE SAME DATABASE AT THE SAME TIME.

 

MANs and WANs are basically networks of LANs.

 

The INTERNET is the ultimate NETWORK OF NETWORKS.

 

Ways in which networks of computers and other devices are connected.

 

Wired and wireless. 

 

"Wire" includes copper wire (POTS, CAT5, and coaxial cable), and fiber optic cable.

 

http://en.wikipedia.org/wiki/Plain_old_telephone_service

 

"Wireless" includes radio waves, infrared, and microwaves. 

 

Connections on a LAN are likely to either be Ethernet (using cat5 cables) or wireless using radio waves.

Connections on a MAN are likely to be microwaves beamed from rooftops or towers.  This requires LINE OF SIGHT.

Connection on a WAN are likely to be microwaves beamed up to a low-orbit satellite. 

 

Of course, you could have a permanent long-distance telephone connection, but the cost would be high and the bandwidth very low.

The Internet can be used to implement MAN's and WAN's and Virtual Private Networks (VPN) can provide some degree of security and assured reliability.

 

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BOTTOM LINE -- It all seems like "magic," but in fact the machines and the connections among machines have physical existence.  Someone in the organization must know how it all physically works in order to keep it working and in order to identify potential problems and security risks.