In the feature on Computer History above, you can see an evolution of computers. The earliest mechanical computers were similar to clocks, using gears to do nothing more than to count at specific intervals. Then came the Jacquard Loom in 1801, which used punch cards, and suddenly we got a new feature: the ability to program. The punch cards input data into the machine, which could then perform calculations. The ability to program a computer—to give the computer various commands which it can follow—has remained central to the definition of a "computer."
Modern computers also defined by a different set of abilities:
- to input data (to send analog data from the outside world into the computer where it is translated to digital form);
- to process data (to change the data according to the programs used);
- to store the data (keep the data in digital form for long periods of time so the computer can easily access it); and
- to output the data (to translate it back to analog form so users can receive it).
You have a digital camera. You take a photo with it.
The analog light, consisting of waves, hits the "CCD" sensor. The sensor changes the light into digital data, consisting of 0s and 1s. For example, one dot which is colored orange might be "111111110111111100000000." These numbers can then be sent into the computer. This is input.
Once the picture is inside the computer, you decide it is too bright. You use an image-editing program to darken the image. The orange dot, for example, is changed from "111111110111111100000000" to perhaps "110111110101111100000000," a slightly darker shade of orange. Your computer has changed the data according to a program. This is processing.
Next, you save the data to your hard drive. This is important, because until you do that, the data could be easily lost. The hard drive, however, is a safe place to keep data for a long time. This is called storage.
Finally, you want to print a photo. You tell your computer to send the data to the printer, which then translates all the digital information into analog form. The printer sprays ink in paper in a way that matches the image stored in the computer. You now have a physical print. This is output.
Here is an image showing you basic parts of a computer setup; you probably have something like this at home, although the exact shapes and sizes of each element will probably differ. Note that there are several input and output devices, which allow for data to go into and come out of the computer in various forms.
Parts of a Computer System
- 1: The Main Chassis, or "body," or "case," or "CPU box"; the housing which holds the motherboard with CPU and RAM, the storage drives, power supply, and often more. The case will have several ports allowing you to connect peripherals (devices connected to the chassis). The chassis may also house speakers, an audio output device.
- 2: The Monitor, a visual output device.
- 3: The Keyboard, a manual input device.
- 4: The Mouse, a manual input device (some computers will have a trackpad).
- 5: A Printer, an output device.
- 6: A Webcam, a video and audio input device (this is sometimes built into the monitor).