Operating System

An operating system is an application (piece of software) that acts as an interface between the computer's hardware and other applications on the computer.  It is also responsible for coordinating what happens when the computer turns on and off.  While it is possible to have two or more operating systems on a single computer, most computers only have one.


Examples
The two most popular operating systems are Microsoft Windows (XP, Vista, and 7)

 and 

Apple Mac OS X (Tiger, Leopard, and Snow Leopard).






A third operating system that is gaining popularity is called Linux, and it comes in widely varying varieties, called "distributions."  The most popular distribution is called Ubuntu (pronounced "oo-boon-two").  Ubuntu is the distribution most similar to Windows and Mac OS X, while other distributions are much more complicated to run, and are mainly used by computer programmers and other people who like to tinker with computers.


Tomorrow: The Internet!

Software

Software is the non-physical part of the computer that is encoded in bits and bytes, rather than hardware, which is the physical part.


Example
Programs and applications are pieces of software, since even though they are sold on CDs (for example), you don't buy it for the CD, you buy it for the information on the CD.


Tomorrow: Operating System

Hardware

Hardware is any piece of equipment that goes into running a computer.  If you can touch it, and it is electronic, it is a piece of hardware.


Examples
Mouses and Keyboards are hardware.  So are computer screens, CDs (compact discs), DVDs, wires, cellphones, TVs, DVD players, remote controls, and lots of other things.


Tomorrow: Software

Program and Application

A computer program or application is what allows people to perform tasks on the computer.  Each application is intended to accomplish a specific task.  Applications are sometimes free, sometimes cheap, and sometimes expensive.  When you open an application, you can use its features, and when you are finished using it, you can save your work, and then quit the application to signal that you have finished using it for the time being.

Examples
One popular application is Microsoft Word.  This application is a word processor: it lets you type and read documents and letters.

Another application is Internet Explorer.  This application is a web browser: it lets you enter web addresses and view web sites on the Internet.

A third application is iTunes.  This application lets you organize and listen to music, movies, and TV shows on your computer.  It also lets you buy new music, movies, and shows from the Internet, and transfer songs to an iPod.






Tomorrow: Hardware

Mouse and Trackpad

A mouse is an input that controls a pointer on your computer screen.  Moving the mouse moves the pointer, and clicking the mouse changes the "focus" of the computer to the location of the pointer.  This change can be to

• type in a different part of an email, report, or letter
• change from one application (or computer program) to another
• click on a button that performs an action (such as to click "shut down" to turn off the computer)
• click on a button that opens up a menu (such as to click "File" to open the menu, then "Save" to save the file)
• or other, more nuanced actions

As computers have developed, manufacturers have tried to clarify the labels on buttons and make the actions that clicking the mouse performs more straightforward.


On some mouses (yes, the plural of "mouse" is "mouses," although "mice" is OK as well), there are two or more buttons, usually referred to as "left," "right," and sometimes "center."  The left button performs the actions described above, while the right and center buttons perform "secondary" actions.  Experiment with your own two-or-more-button mouse to discover which actions are triggered by the right and center buttons.


Laptops (portable computers) do not use ordinary mouses, since it is inconvenient to keep track of the computer and the mouse while traveling.  Instead, they use trackpads, which serve the same purpose as mouses do yet are built in to the laptops.  Instead of moving the mouse to move the pointer, you slide your finger along the surface of the trackpad.  Most trackpads have a button (or buttons) to click, just like a mouse.  In addition, though, newer trackpads will often "click" when you tap your finger on the trackpad surface instead of the mouse.  This allows you to move the mouse and click without looking down at the trackpad to make sure you are touching the right surface.


Example
A two-button mouse

A trackpad on a laptop

Tomorrow: Program and Application

Keyboard

A keyboard is an input that allows you to input letters, numbers, and symbols into a computer. It also has special keys called "modifier keys" such as Shift, Control (or ctrl), Alternate (or alt), Function (fn), Command (z) or Apple ().  These keys do not produce letters or symbols when you push them.  Rather, they change what happens when you push other keys at the same time.

• The Shift key changes lowercase letter keys to capital letter keys, and changes number keys to symbol keys.  For example, pressing the A key gives "a," but pressing shift and A gives "A."
• On a Windows computer (Dell, HP, Toshiba, Sony), the Control key, in combination with another key, can perform an action, similar to the "function keys" below.  For example, pushing Control and s at the same time will save your current work on the computer.  Control and p will print the current page.
• On an Apple computer, the Control key is not used often.
• The alt or option keys change both letters and numbers to other characters.  For example, pressing option and s gives "ß," or option and t gives "†."
• The fn key is not used often.

Keyboards also have "function keys," which are usually in the row above the number keys.  Function keys are labeled F1 through F12, and when you push them, they have the computer perform a certain action (other than typing a letter).  Finally, the Escape key (esc) can do different things depending on the particular computer and keyboard.


Example

The Apple Keyboard

Notice the shift, fn, control, alt/option, and command "modifier" keys in the lower-left corner.  Also notice the "function" keys on the top row, some of which are labeled with their intended "actions," or functions.


Tomorrow: Mouse and Trackpad

Output

An output is an interface that converts bits and bytes from a computer into information that makes sense to people.  Output can also refer to the bits and bytes themselves, or to the information given by the output.


Example
A computer screen is an output, since it converts information from the computer into information you see on the screen.

Another output in this picture is the set of speakers, since they convert bits and bytes into sound.


Tomorrow: Keyboard