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Pretest study guide for computing systems and networks


* This page is under construction 

It is highly recommended that you review the official study guide and use the practice questions on pages 20-29 at for College Board test 5652 CS Praxis II official study guide. Pay special attention to questions 2-4,6,12-13,20-25

Computing Systems are made up of hardware and software.

  • Hardware are the physical devices you can see and pick up: screens, printers, chips, etc.
  • Software are the instructions that control the hardware: operating system, apps, programming environments, etc.


Input, output, and the CPU

Computing systems receive input in many ways: keyboards, cameras, sensors, etc. They store the information and process it to produce different kinds of output: motion, printouts, pictures, words, etc.
The central processing unit (CPU) fetches instructions from memory, decodes what they mean, and then executes the commands.

The video series explains the inner working of computing systems at an introductory level.

Binary and levels of abstraction

Computers store information in binary code which consists of only 0's and 1's. You can learn about how binary code works here.

Levels of abstraction help us understand systems and problems by focusing on each of the parts that make up a whole system one level at a time. At the lowest level of abstraction, a computing system is made up of electronic signals that pass through chips on circuit boards. These bits of information (Binary Digits), are grouped together in groups of 8 to form bytes of information. These bytes are interpreted by the computer in many ways such as letters in words, digits in numbers, or pixels (dots of color) in pictures. At a high level of abstraction, the user can see the words on the screen, a picture, or hear sounds without needing to understand the details of how the bits are arranged and flow through the system.

Information is stored in the system in bytes. To understand the size of KB, MB, GB, TB, etc. see this chart.

The internet

The internet is a complex, worldwide system of communication with millions of devices all connected to each other. If you need to learn the basics of how the internet works, watch this video series and be sure you can answer the questions provided and define the vocabulary listed for each video. 


There are many threats to communication on the internet. Many are covered in the video series. In addition, teachers should be familiar with the 5 pillars of cybersecurity

  1. Confidentiality: Protection of information from disclosure to unauthorized individuals, systems, or entities. Only the right people can see the data.
  2. Integrity: Protection of information, systems, and services from unauthorized modification or destruction. The data is protected.
  3. Availability: Timely, reliable access to data and information services by authorized users. The services are available to the people who need them when they need them.
  4. Non-repudiation: The ability to prove that information is coming from where it says it is coming, and the person using it is the person who has the right to use it. more details here.
  5. Authentication: The ability to verify the identity of an individual or entity. Authentication is entity oriented.

These describe the basics of information protection. There is some overlap between the Pillars of Cyber Security. Often a defensive measure will protect multiple pillars. In many cases, a particular attack will violate more than one. 

There are many common attacks to information security. It would be good to be familiar with the most common attacks as outlined in this Cisco article.























Notes under construction:



The Big Picture

Chips and circuit boards

How the CPU works

Binary and number systems

Measuring computer storage

Operating Systems

Application programs



Levels of abstraction (some examples)

Cybersecurity concepts



Using IPO: hw/sw input output

Programming software level Algorithm program, OS, code, interpreter, compiler.

Creative commons is a system designed for sharing digital intellectual property. Here are some commonly used license options


Read more at _____

The operating system is essential to making a computing device work. It is the software that controls the system. It allows parts of the computer to communicate, organizes the computer’s storage areas, displays the time and error messages, and does all of the background work so that application programs can each do their own, specialized work. Application programs like games, word processing, spreadsheets, email, and browsers (programs to view web pages on the internet) each have a special purpose to perform.

Another common application program is a simulation that is used in business, finance, weather prediction, traffic patterns, engineering, and even psychology. A simulation is based on a model of something in the real world. The programmer chooses which factors to consider and how to describe the way they interact. Then the computer runs the program to try out a scenario and collect data. This helps people to design better structures and make predictions about what could happen in the real world. Adding more variable, or details, to a model makes it more accurate but requires more time and computing power to run the program.

People can write programs for a computing system using a variety of high level languages (coding languages that are made to be as easy as possible and powerful for people to use. Examples would be Python, Java, JavaScript, R, Ruby, etc.). Computer programs, called compilers, translate the instructions into a form that the computer can understand and process. Sometimes an interpreter is used instead of a compiler because it translates one piece at a time and executes the instructions one at a time, which makes it easier to catch mistakes.

Physical hardware level Circuit level: body nerve impulses electronic signals.

The inside of a computer is made of chips connected by circuit boards. The chips store information using microscopic switches that can only be on or off. Instructions and information are all stored in a binary code of 0’s (off) and 1’s (on).

CPU fetch execute

If you are not familiar with binary (Base 2) number systems. View this video to understand how it works. Our normal number system (Base 10) uses 10 digits 0-9. The hexadecimal (Base 16) number system is used as a shortcut for binary and uses the digits 0-F. (use letters when you run out of numbers) For the quiz, you should be able to convert small numbers back and forth from binary, to decimal to hexadecimal. Here is a place where you can practice.

0 1 One, individual binary digit (a single 0 or 1) is called a bit (short for binary digit)

8 bits put together make one byte of storage, just enough to store a single letter in a word.

Computer storage is measured in byles:

Piece of paper KB = kilobyte = about 1,000 bytes

Fat encyclopedia MB = megabyte = about 1 million bytes

Room in a library GB

Video collection TB

Example of a computing application:

Watch a movie online.

High level abstraction

Middle level

Low level

Cybersecurity: short summaries

Common attacks

The 5 pillars of cybersecurity

Trojan horse


Man in the middle attack



1.     Integrity

2.     Authentication

3.     Nonrepudiation


For the actual exam it would be helpful to know about encryption / decryption schemes, vocabulary, common protocols and addressing systems.

Programming and expressions

Computers execute instructions sequentially from beginning to end. Variables allow programs to store information, modify it, and retrieve it.

A computer program that could calculate the monthly payment for a $20,000 loan at 5% over


Dianne O'Grady-Cunniff, dogrady at usmd dot edu
Director, Maryland Center for Computing Education

Dr. Megean Garvin, mgarvin at usmd dot edu
Director of Research, Maryland Center for Computing Education

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Maryland Center for Computing Education
3300 Metzerott Rd. Adelphi, MD 20783
MCCE received initial support from the National Science Foundation, (MSP)2 Grant No. 0831970.