1.2+Data

=Data=

//Before you begin//: Lessons are based on community-based, continually updated online sources such as [|Wikipedia]. Relevant terms for this lesson are listed under Topics and presented in a narrative format in the Read about sections. Click on each of the linked items and visit the Wikipedia article to get the most out of the lesson, and then hit the Back button on your browser to return to the lesson.

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=Goals=
 * To learn about the nature of digital information
 * To know the difference between analog and digital signals
 * To be familiar with data compression algorithms and why they are performed

=Topics= [|transistor], [|bit], [|byte](kilo-, mega-, giga-, tera-), [|analog], [|digital], [|file], [|directory], [|folder], [|backup], [|data redundancy], [|American Standard Code for Information Interchange](ASCII), [|Unicode], [|standards]

=Read about=

Numbers and Characters
Computers speak in the language of 0's and 1's, also known as the [|binary number]system. If you think about all the tasks we rely on computers to do today, there's quite a //bit// you can do with these two numbers. [|Bits and bytes] represent units of data that can be processed by computers. One [|bit] holds one number, which can be either 0 or 1. One [|byte] holds 8 bits, or a series of eight 0's and/or 1's.

Since each bit can hold one of two values, a byte can therefore hold 2⁸ or 256 possible states. One byte can thus represent any integer number from 0 to 255. Two bytes can represent any integer from 0 to 65,535. Increasing aggregates of bytes (kilo-, mega-, giga-, tera-) can improve precision indefinitely, while adding information about the positive or negative sign of a number.

Calculations in the binary number system may be performed using [|Boolean logic]. Physical implementation of Boolean logic can be performed by representing 0's and 1's with "high" and "low" voltages over wires, using electronic [|gates] or [|relays]. This is the idea behind computer "chips" which perform the complex data processing we expect from computers today.

Similarly, alpha-character data can be represented by sequences of 0's and 1's. The most common [|standards] used for alpha-character data (regardless of font family) are [|ASCII] (American Standard Code for Information Interchange) and [|Unicode].

A [|file], whether a word document or an image or a spreadsheet, is viewed in its simplest form by the computer as a sequence of binary data. Numbers, characters, images, sounds, etc. are all stored as a sequence of 0’s and 1’s. Files are stored in [|folders], also known as [|directories].

Images and Sounds
[|Images] can be subdivided into very small points, which can then be represented as numbers assigned to colors within a predefined palette. Similar to a painting consisting of dots of color ([|Pointillism]), the smaller and closer the dots are to one another, the better the [|resolution] of the image will be. Numbers representing the [|color] and intensity at each of these dots can be converted to binary code and transmitted to a receiving computer. The receiving computer then converts all of those numbers back to the image, which then appears on the screen. A [|Video Graphics Array] (VGA) interface used in the old [|Cathode Ray Tube] (CRT) monitors required the computer to convert the digital data to analog signals in order to display the image, while the newer digital interfaces such as [|Digital Visual Interface] (DVI), [|High-Definition Multimedia Interface] (HDMI), and [|DisplayPort] allow the digital data to be transmitted directly to the [|LCD] (liquid crystal display) panel without the conversion to analog, improving image quality.

What we hear as [|music]and voices speaking are [|sound] waves causing physical movement in our eardrums. These waves are perceived in terms of pitch and volume by the brain. An absolutely pure tone looks like a [|sine wave]. Compared to this, a person’s voice coughing, talking, or singing has a funny “lumpy and bumpy” shape. Given enough sampling, any wave can be [|represented by numbers] that stand for the amplitude of the wave at each point in time. These numbers can then be sent between computers in binary format. The function of “[|sound cards]” in computers is to turn analog information (e.g. a human voice saying “hello world”) to digital information during sound recording. They also perform the opposite function when computers play digital music files (i.e. found on [|CD], or [|mp3]) over their speakers.

Analog vs. Digital Signals
Binary data is easily converted into [|analog or digital signals] because it only has two states, 1 and 0. Over a wire in [|digital signaling], these two states can be represented by pulses of electricity or light, and be sent from one computer to another. The receiving computer can then decode the signal by transforming the binary code back into letters or numbers. Alternatively, a way of conveying binary information via [|analog signaling] can be by [|frequency modulation] (FM) or [|amplitude modulation] (AM); these signals may be sent "[|wirelessly] ." Other kinds of [|modulation]can be done to [|transmit sound] over analog or digital networks.

Compression
If you can imagine [|sending a video] that has both sound and images changing at multiple frames per second, the amount of data to be sent quickly becomes enormous. [|Compression]is a useful transformation of the data that reduces redundancies and eliminates certain unnecessary components (in lossy compression), thus creating a smaller data set that is sent more efficiently. [|Files may become compressed] using programs like [|WinZip] or [|Stuffit].

=Activity=

#1: Answer the following questions

 * What is the difference between a folder and a directory?
 * What is the difference between a technical standard and a natural standard (e.g. the speed of light)?

=Online resources=
 * Henricks WH, Boyer PJ, Harrison JH, Tuthill JM, Healy JC. [|Informatics training in pathology residency programs: proposed learning objectives and skill sets for the new millennium] . Arch Pathol Lab Med. 2003 Aug;127(8):1009-18.

=Questions= Take the online [|quiz] after going through the readings from this lesson.

=Advanced courses=
 * Wikipedia Article on [|Information Theory]
 * Aziz Boxwala, Omolola Ogunyemi, Qing Zeng. Course materials for HST.952 [|Computing for Biomedical Scientists, Fall 2002]. MIT OpenCourseWare, Massachusetts Institute of Technology.
 * Seth Lloyd, Paul Penfield. Course materials for 6.050J / 2.110J [|Information and Entropy, Spring 2008]. MIT OpenCourseWare, Massachusetts Institute of Technology.

=Expert corner= Help needed with Wikipedia article(s): [|computer file]

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