Operating System + Computer applications
OS led to Microsoft's
"accidental" rise to become one of the world's largest companies and Bill Gates one of the world's richest men. Bill Gates and Paul Allen were high-school friends. While Bill was in college and Paul a programmer, they learned about new low-cost microcomputers—today's PCs. Gates and Allen thus started Microsoft
process
(also known as task) is an independently running program, perhaps a user's app, or an OS app, or part of a larger app (one app may run several processes).
Microsoft
(short for Microcomputer Software) in 1975 to create and sell an implementation of the BASIC high-level programming language for a particular PC of that time.
Common video formats and player apps:
1) AVI (Audio Video Interleave) (file suffix .avi) is one of the oldest video formats, developed by Microsoft in 1992. Widely supported, but compression and video quality may not be as good as others. 2) Flash video (file suffix .flv or .f4v) is a video format primarily designed to play in Adobe's Flash Player. Flash video is popular today in part due to wide use by YouTube. 3) WMV (Windows Media Video) is a video format developed by Microsoft for streaming video via the Internet. File sizes are typically small but quality may be poor. A special player may be needed for viewing on non-Windows devices. 4) MOV (Apple Quicktime Movie) is a video format developed by Apple for their Quicktime video player. The format is known for having high compression while maintaining quality. 5) MP4 is an international standard video format, since the early 2000's. MP4 is similar to the MOV format, known for having high compression while maintaining quality. MP4 is growing in popularity due to being made part of HTML5, meaning most modern web browsers can play MP4 video.
NeXT Computer.
After leaving Apple, Jobs founded this new company (During that time, Jobs also co-founded Pixar, the animated movie company responsible for Toy Story and other hugely-popular movies). NeXT developed an OS named NeXTSTEP based on Unix, to run on Next computers. NeXT was not particularly successful. However, by 1996 Apple was nearing bankruptcy, so Apple bought NeXT and brought back Jobs. NeXTSTEP formed the basis for Apple's new OS called Mac OS X, which is the main OS for Apple's computers today.
Mac OS
Apple developed an OS for Apple computers. Apple became a billion-dollar company by the mid-1980's. However, Windows PC's dominated the market, and Jobs clashed with other Apple executives about the company's future directions. This situation prompted Apple's board to strip Jobs of most duties; without duties, Jobs resigned.
formatting features: Bold, italics, underline.
Bold: Bolded text is thicker/darker than usual. This text is bold. Italics: Italicized text is slanted.This text is italicized. Underline: Underlined text has a line underneath. This text is underlined.
Huffman encoding
algorithm measures the frequency of each data item like each letter, and gives the most frequent items a shorter bit encoding (like the letters "a" and "e"), with least frequent items getting a longer encoding (like letters "q" and "z"). Many compression techniques combine LZ and Huffman algorithms.
audio player
app plays an audio file such that the audio can be heard, by sending numbers one at a time to a digital-to-analog converter, at the specified rate.
Windows graphic
graphical OS (originally built on top of DOS). One may find interesting that the opportunity that made Microsoft into one of the world's large companies was initially declined by Gates and considered relatively unimportant at the time.
Windows the Task Manager app
help determine which apps are using the most CPU or memory. Guided by this information, a user can know which apps to quit.
Mac OS X provides the Activity Monitor app
help determine which apps are using the most CPU or memory. Guided by this information, a user can know which apps to quit. .
Audio apps
iTunes (comes with Macs, iPhones, iPads, and other Apple products), Windows Media Player (for Microsoft Windows products), and a built-in music player for Android devices. Popular computing devices also come with apps for audio recording, such as Quicktime or Garage Band for Macs. Apps for editing audio files such as getting excerpts or mixing music are also available, such as Garage Band for Macs, or the free Audacity app.
Formula
in a cell (خلية) to compute that cell's value based on other cells' values. The formula begins with = followed by a math expression using operators like +, -, *, /, and parentheses (). Another cell's value can be included using that cell's row letter and column number, as in: = 3 * A1.
methods to clean up a drive:
1) Delete some movies, songs, and photos: Movie files are huge, often several gigabytes, so usually the first to go. Songs and photos are large, often many megabytes, but in high quantities can add up to a lot. On a smartphone or tablet, these items are often the main contributors to drive usage. 2)Delete some PDF files: Some PDF files (like for entire books) can be hundreds of megabytes. 3) Remove temporary Internet files: Web browsers may make local copies of a web page's images, so a next visit to the page is faster (saving time by not downloading the same image over the Internet). Such browsers usually have built-in cleanup options. 4)Remove/uninstall some apps: Some apps can be quite large. 5)Empty the recycle/trash bin: Many OSes give users a chance to "undelete" a deleted item, by placing deleted items in a recycle/trash bin. When cleaning up a drive, a user may need to tell the OS to empty the bin—of course, after ensuring that items really aren't needed.
Presentation apps typically contain three types of tools
1) Editing tools enable users to add static elements such as slides, formatted text, figures, and graphics. 2)Animation tools give movement to static elements. Users specify a timed list of animation effects such as appearing, disappearing, or changes in position within the slide. 3)Presentation tools display the completed slideshow, typically by connecting a cable to a projector that displays on a large screen. Presentation apps may also contain multimedia tools to enable the integration of audio or video within a slideshow.
An OS has several duties
1) Hardware interfacing ربط الأجهزة: Hide complex details of interacting with hardware devices like a keyboard, screen, mouse, drive, USB, network, etc. The OS portions that interface with hardware are often called device drivers. 2)File management: Allow users to create and organize files, keeping track of file locations on a drive. 3)Multitasking: Support multiple applications running seemingly simultaneously, but actually running a bit of each application one at a time, switching thousands of times per second. For multiple users, the OS keeps each user's items separate from other users' items.
Common file types and extensions.
1) PDF: (pdf)A PDF file, short for Portable Document Format, describes formatted text/graphics suitable for viewing and printing, independently of apps like a word processor, web browser, etc. PDF is an open standard (previously proprietary to Adobe Systems). PDF files are usually for viewing/printing only and are not edited by a user, but rather are produced by another app like a word processor. 2) Microsoft Office document (.docx*.pptx*.xlsx) A Microsoft Office document file is used by the Microsoft Word (.docx), PowerPoint (.pptx), and Excel (.xlsx) apps to save each apps' files in a way suitable for later editing. 3) Executable تنفيذ file (*exe (Windows)An executable file is an application; executables for Windows typically end with .exe. 4) Media file (*.jpg*.png*.mp4 *.mov*.mp3) A media file stores a picture (jpg/png), video (mp4, mov), audio (mp3), or other media item.
some common cases
1) a user accidentally deleting a needed file, many operating systems don't really delete the file from the drive, but rather move the file to a special folder called trash or a recycle bin. The user can thus recover an item from the trash. Every so often, a user may need to empty the trash, to free up space on a drive. 2)A common and usually very upsetting situation is that a user cannot access a drive's files to a hardware failure or a corruption of the drive's data causing the OS to fail to find files. However, the files may still be retrievable from the drive. Some software applications specifically search the drive for recoverable files (which may require connecting the drive to another computer that can run that software). Some companies also specialize in recovering files from failed drives, though such services are often costly. 3)Drive failures are quite common. About 5% of hard drives fail within 3 years; for drives from some manufacturers, the rate is 20% (source). A good OS user expects such failures and thus makes backups.
Apple Computer
11 years later of founder Steve Jobs led to Apple's popular Mac OS X operating system. Steve Jobs and Stephen Wozniak were friends in the early 1970's in northern California due to common interests in electronics and computers. Jobs and Wozniak in 1976 to build personal computers, a new and exciting kind of computer at the time.
Device drivers برامج تشغيل الأجهزة
A computing system is typically a combination of hardware, like a screen and keyboard, and software, like an operating system (OS) and applications. The OS portions that interface with hardware are often called device drivers Ex: Upon connecting a new printer (hardware) with a computer, the OS may require installation of device driver software so that the OS can send proper print commands to the printer. Modern computing systems (especially tablets and smartphones) often come with built-in device drivers or install device drivers automatically, but sometimes a user (especially of desktop or laptop computers) must deal directly with installing or updating a device driver.
Quitting running apps
A user commonly doesn't quit previous apps before running another app. A multitasking OS may continue to run those previous apps, which occupy valuable CPU time and memory, causing the user's current app to run slowly. Thus, a good OS user takes time to occasionally quit unused apps.
cursorالمؤشر
A word processor uses a cursor, typically a vertical blinking line, to indicate where a user's next-typed text will appear. The user can move the cursor using a mouse or finger, or using a keyboard's arrow keys. A word processor typically has icons or menu items that allow a user to format text, such as bold, italics, or underline. The user can first select some text (e.g., using a mouse), and then change the text's format. Or, the user can place the cursor somewhere, select an icon (which then appears as "on"), and begin typing.
Example problems include:
Computers (desktops, tablets, smartphones, etc.) don't always perform as desired, instead exhibiting a problem. Example problems include: The computer won't turn on. The computer is slow. The computer won't communicate with a printer or other device. An app won't run, or runs and then exits. An app is behaving badly, such as showing popup ads. By far the most common solution to computer problems is simply to restart the computer (and/or other device), or restarting just the failing application. The reason such a restart commonly works is that bugs exist in nearly all computer software, including applications and operating systems. The longer that software runs, the more likely that a bug will be encountered that causes the software to run poorly, to use up excess memory, etc. Most computers today go into a "sleep" mode when shut or turned "off", so the normal process of ending a working session with a computer is not sufficient—a restart may require a more deliberate set of steps.
Data
Data is a collection of facts and values. Ex: 23, 35, 48 is data.
cleaning up a drive
Deleting largest items first is logical. A user might copy less needed items to a portable drive or cloud storage before deleting. a nearly-full drive may cause apps to run slowly, as the apps and OS struggle to find drive space. Thus, a good OS user should occasionally remove unneeded files, folders, and apps,
several kinds of databases.
Each kind of database is characterized by the method data is organized. 1) A relational database (قاعدة بيانات علائقية) stores information in tables composed of rows and columns. Relational databases contain the following: --Field (column): Basic unit of data stored --Record (row): A group of related fields --Primary key: A record's unique identifier --Table: Collection of related data 2) Multidimensional databases store(تخزين قواعد البيانات متعددة الأبعاد) data in more than two dimensions. For example, a multidimensional database may contain multiple inventory tables with time as another dimension. 3) object-oriented database stores data as a collection of objects rather than tables. An object may consist of an ID, photo, and title, while another object may consist of a ID, video clip, and runtime.
bit depth
Each sampled audio value is stored using a fixed number of bits commonly 16 or 24 bits. Thus, an audio file can simply be a series of 0's and 1's, such as 0000000000000001 0000000000000010 0000000000000011 0000000000000011 etc. (representing numbers 1, 2, 3, 3). Of course, values typically span the range of possible values, such as 0011110111011110 or 1111000000000011. Audio files may be large. If each sample's number requires two bytes, the sampling rate is 44,100 samples/second, and a song is 3 minutes (180 sec), then a song's audio file would require about 180 sec * 44100 samples/sec * 2 bytes/sample = 16 MB (megabytes, or million bytes). Audio files are usually stored in compressed form to reduce file size. As such, a typical song file might only be about 4 MB. Common compressed audio file formats include mp3, AAC, and AIFF. A common uncompressed format (primarily for Microsoft Windows PCs) is the WAV format.
Font
Font refers to particular text style features, such as the shape, thickness, and spacing of text characters. Commonly-used fonts include Arial, Times New Roman, and Courier New, illustrated below Arial font has smooth straight lines. Times New Roman font uses varied line-widths, including tiny lines at the tips of characters known as serif. Courier New font uses equal-width plain-looking characters that were common on manual typewriters several decades ago. Note that the horizontal space per character varies in the first two fonts (e.g., an i takes less space than an h).
IBM Computer company
IBM asked Gates for an operating system for the IBM PC, but Gates declined—perhaps because a PC's operating system back then was just a boring small piece of software, whereas BASIC seemed like the future of software. Gates referred IBM to another company, but no deal was made, so IBM returned to Gates. This time, Gates purchased an existing OS (originally named QDOS for Quick and Dirty Operating System) from another company for $50,000, and introduced the OS as MS-DOS in 1981. BASIC turned out to be relatively unimportant, whereas MS-DOS use grew to millions of users within a few years, eventually leading to the Windows
themes
Presentation apps contain a library of slideshow themes consisting predefined color palettes, backgrounds, and text formatting to provide a cohesive style throughout the presentation. If no theme is selected, then slides will default to a white background and default text formatting.
filename extension اسم الملف
Several types of files are common, such as PDF files (for formatted documents), and JPEG files (for images). Different file types typically have a different abbreviation after the filename's period such as myfile.pdf for a PDF file. The extension informs users and applications of the file's type.
memory leak
The longer the app runs, the more memory the app uses, even though the app doesn't really need the additional memory. Memory leaks are caused by certain bugs in the app, but apps aren't perfect so leaks are common. Leaks are especially noticeable in web browsers, which tend to be left running without quitting for long periods. Thus, a user may find that quitting and restarting an app, perhaps every few days, results in less memory usage and thus faster-running apps.
The animation tool contains a library of effects that give movement to text and graphics:
Type of effects-- 1)Fade in causes an object to gradually appear. 2)Fly in causes an object to appear beyond the slide's margin to the original location. 3)Zoom in increases the size of the object from very small to the original size. The library of animation effects and animation tool interface varies with the presentation app. when to apply the effect--- 4) On click executes the effect when the user clicks the mouse. 5)After previous automatically executes the effect once the previous animation effect is completed. 6)With previous executes the animation with the previous effect, grouping animation actions together into a single effect. the speed of the effect--- 7)The speed of each effect can also be configured. Animation effects also apply to slide transitions. As the slideshow progresses from one slide to the next, slides can dissolve, rotate, or move to reveal the next slide. Transition effects vary with the presentation app.
Google Docs presentation
Using Google Docs presentation slides app, choose a slideshow theme and add two slides. The first slide is a Title slide. The second slide is a Title and Two Columns slide. Duplicate the formatted text, box shapes, and text box in the slides above.
LZ compression
algorithm (named for creators Lempel and Ziv) examines data for long repeating patterns such as phrases, and creates a dictionary entry for such patterns
portability قابلية التنقل
With such abstraction, the same application program can run without modification on different kinds of computers Common operating systems include Windows, Mac OS X, and Linux for desktop computers, and iOS and Android for tablets and smartphones.
operating system (or OS) نظام التشغيل
a program that implements the detailed interactions with hardware (among other things), presenting an application program with a more abstract interface like "Display '6' to the screen". is a special program with various duties, such as interfacing with hardware (providing a more abstract view to applications), managing files and folders, and running multiple applications seemingly simultaneously (multitasking) for one or more users.
MP3 and OGG
are audio compression techniques. Audio is captured electronically as varying voltages on a wire. Those voltages are converted to numbers for digital storage. An uncompressed 3-minute song may require tens of megabytes. MP3 and OGG compression use techniques (introduced above) like converting to frequency domain, quantization, and Huffman coding. A 3-minute song may be compressed to just a few megabytes. MP3's name comes from MPEG, as MP3 was used for compressing the audio part of video files. OGG was developed as a free open-source audio compression technique.
Video files
can be quite large. If a single image required 1 MB, then at 30 frames per second, 100 minutes (a common movie duration) would require 100 min * 60 sec/min * 30 frame/sec * 1 MB/frame = 180,000 MB or 180 GB. Common video file formats, such as MP4, H.264, or MOV, differ in how compression is used to reduce video file size. The key idea of video compression is to only store some frames completely, with most other frames stored as the difference from the previous frame (in a video, such differences between successive frames are typically tiny). Video compression usually loses some quality. After compression, a 100 minute movie may only require 5 to 10 GB. Most devices that record video do compression while recording, and devices that play video automatically decompress
toolbar
displays a strip of icons corresponding to available operations. In Google Docs' presentation app, the plus sign icon adds new slides to the slideshow. Other presentation apps may use different icons. Users can choose to create a new slide from a set of templates.
Validation التحقق من صحة
ensures data is correctly entered as the data is added to the database. Periodic updates to the database ensure data is up-to-date.
Backups
file is a copy of a file intended as a replacement in case the original file is lost. Backup files are important, because files are lost quite commonly, such as when: **A user accidentally deletes a file. **A user accidentally overwrites a file with different content. **An app with a bug corrupts a file during a save such that the file can't be re-opened. **A computer is stolen, or damaged due to falling in water, being dropped, etc.
WAV
file stores audio uncompressed.
Unix the top app
for seeing each app's CPU and memory usage. Such a monitoring app may refer processes.
The SQL "SELECT"
instruction queries the Inventory table for any recording matching the "WHERE" criteria. In the first example below, the query returns all fields (as specified by the * operator) of records whose Category field contains 'Watch'. The first two records contain 'Watch' in the Category field. As a result, the values of all fields corresponding to the first two records are displayed. The second query returns the Cost field of all records whose ItemNo field contains 'T731'. The last record matches the user criteria. The query displays the Cost field, which contains 38.41.
manual backup دليل النسخ الاحتياطي
involves a user intentionally copying files to another location. That other location should be separate from the file's drive, such as a USB drive or an external hard drive, or a location in the cloud. The cloud is useful due to less chance of one incident damaging both the original file and the backup, such as theft, or a fire EX: Google Drive and Dropbox.
database قاعدة البيانات
is a collection of data organized to enable efficient information retrieval. A company may use a database to gather information regarding current inventory or to forecast trends. A database may be on a local computer, but is commonly kept by a network server.
file
is a collection of information stored somewhere on a drive, such as a music file, movie file, word processing file, or an application. A user may wish to organize files using folders
word processor معالج الكلمات
is a common computer application for creating formatted text
spreadsheet application تطبيق جدول البيانات
is a common computer application for representing tables of data like text or numbers, for using formulas to calculate data from other data (like sums or averages), and for creating graphical charts from data. A spreadsheet contains cells organized into columns labeled A, B, ... and rows labeled 1, 2, ...; a spreadsheet user can type data in each cell.
zip file
is a common file format for combining multiple files into one file and that usually involves compression. Ex: Using a zip app on a Mac, a 4 kbyte file named index.html was converted to a 2 kbyte file named index.html.zip.
JPEG
is a compression approach specifically for images. An image may consist of millions of pixels (short for "picture elements"), each pixel being a colored dot. A pixel may be 3 numbers (each a byte) indicating the amount of red, green, and blue. If an image has 4 million pixels, and each pixel requires 3 bytes, then a single uncompressed image is basically just a series of 12 million numbers (so 12 Mbytes). JPEG compresses the image using several techniques. 1)One is to convert to the "frequency domain", which is beyond this material's scope. 2)A second is to use Huffman encoding. Ex: An image with a lot of bright pixels may have millions of "255" values for pixel colors. 255 in binary is usually 11111111, but Huffman encoding may create a dictionary entry like 01: 11111111, so those millions of 11111111's can be replaced by 01's. 3)A third compression approach is to round the numbers, known as quantization. So a pixel of 255 red, 64 green, and 231 blue (which is a shade of purple) may become 25, 6, and 23. Decompression might append a 5, yielding 255, 65, and 235, which is an unnoticeably different purple than the original. JPEG is lossy compression, due in part to the rounding (as well as conversion to frequency domain). Image apps may allow a user to reduce file size, achieved by losing more information, such as by doing even more rounding. The loss in quality may not be noticeable unless the image is enlarged.
MPEG
is a compression approach specifically for video (a recent well-known version of MPEG is MP4).
presentation app
is a computer application used to create a slideshow of text and graphics, often with animation. A slideshow consists of a series of individual "slides". Work or school presentations are often accompanied by a slideshow to help the audience visualize information. Popular presentation apps include PowerPoint, KeyNote, Impress, and Google Slides (part of Google Docs) Presentation files are stored using special filename extensions such as .ppt, .pptx, .odp, or .key.
iOS
is a graphical OS developed by Apple in 2007 for Apple smartphones and tablets. A key iOS feature is that most user operations involve touching the screen, using multiple fingers and gestures (like swiping or pinching), rather than typing or using a mouse. iOS has some Unix basis.
Mac OS X
is a graphical OS developed by Apple in the early 2000's, based on the Unix OS. Mac OS X was preceded by early Mac OS versions dating back to 1984, which were not Unix-based.
Windows
is a graphical OS developed by Microsoft in the mid-to-late 1980s. Windows was originally a simple graphical interface to MS DOS, but later versions were developed new without MS DOS and with powerful graphical features.
Android
is a graphical OS released by Google in 2007 for smartphones and tablets, based on the Linux OS. Android also emphasizes interactions via screen touches.
folder
is a grouping of files or other folders, that helps a user organize items. A role of an OS نظام التشغيل is to manage files and folders, keeping track of such items' locations on a drive, making such items visible to a user, and allowing a user to open files or run apps.
H264
is a more recent video compression approach than MPEG, intended to reduce bits further for fast transmission of video over networks. Video compression is lossy, in part due to the images being compressed using JPEG (which is lossy), and more so because predicted frames clearly aren't entirely accurate. Video apps may support different quality levels, with lower quality achieving smaller file sizes via use of more predicted frames and more-compression of images too. Video compression amounts of 50x-100x or more are common.
multi-user OS
is a multitasking OS that runs multiple users' applications, keeping each user's applications and files separate, and switching among applications fast enough (typically thousands of times per second) to give the user the illusion of being the only user on the computer. Desktop operating systems like Windows and Mac OS X also support multi-users but are commonly used by a single user.
QL (Structured Query Language)
is a popular language to run operations on databases. SQL became a standardized language in 1986 and is used in a number of DBMS' such as Oracle Database and Microsoft Access. MySQL is a freely available database system that uses SQL. MySQL is a popular database for web apps. Users or programs access the database through a set of operations. The SQL "INSERT INTO" operation adds new data to the database. Users specify the name of the table to which new data is added, the fields for which data is being specified, and the value of each field.
Troubleshooting استكشاف الأخطاء وإصلاحها
is a process of determining the cause of a computer problem, and ideally solving the problem. Experienced troubleshooters may follow a methodical two-step troubleshooting process: 1) Predict a probable cause of the problem, and 2) Test the prediction by doing something to confirm or deny the prediction. If not confirmed, repeat step 1 (possibly with a different prediction).
application تطبيق app
is a program that a user runs to carry out a user task like listening to music or surfing the web. To carry out a task, an application may have to interact with a keyboard, mouse, screen, USB device, WiFi, etc. he details of such interactions may be complex, involving specific writing/reading sequences of particular memory locations. Ex: On one computer, printing to the screen may involve writing data to memory locations 57, 58, and 59; on another kind of computer, to locations 3041, 3042, and 3043.
Video
is a series of images called frames. If shown faster than about 15 frames per second (movies use 24, TVs use 30 or more), a human's vision system sees the images as a continuous video. The key idea of video compression is that successive frames differ only slightly, so a frame can be represented just as the difference from the previous frame. Ex: Frame 1 may be a full image, but Frame 2 may just be "Previous frame shifted left 2 pixels". Clearly not all frames can be represented as the difference of another frame. Thus, such video compression sends an image frame and then perhaps 10 "predicted" frames, followed by another image frame. Note: Image frames are also compressed using image compression like JPEG.
Video
is a series of slightly-differing images shown fast enough to appear continuous to humans. Each image in video is known as a frame, and the number of frames per second (fps) is the frame rate
dictionary
is a table of shorthand versions of longer data. Ex: Given a dictionary of 1: Department, 2: of, and 3: Redundancy (1, 2, and 3 are the shorthand items), then "1 2 3 1" is short for "Department of Redundancy Department". The compressed file will contain the dictionary itself plus the data in shorthand form, which combined is hopefully smaller than the original file. A typical text file might be compressed by 50% or more.
slide master
is a template that stores theme information and defines the layout of text boxes, colors, fonts, and formatting. A set of slide masters can be defined for common slide types, such as Title slides or Title and Body slides. As a new slide is added to the slideshow, the new slide is copied from the slide master and takes on the same layout and formatting of the slide master. Any change to the slide master is applied universally to all copies within the slideshow. Users click on individual text boxes to add new text. Additional text boxes and graphics can be added to the slide using the toolbar options. Standard text formatting options also appear in the toolbar.
Linux
is a version of Unix developed in the early 1990's by Finnish college student Linus Torvalds, with Linux popular today due in part to being free and open-source, and with people around the world continuing development. Linux was originally text based; popular Linux versions today like Ubuntu have a graphical interface.
Unix
is an OS developed in the late 1960's by AT&T Bell Laboratories, focusing on multi-user support, and written in the C high-level language rather than assembly to ease implementations on different computers. Unix is text based, requiring typing to view, copy, move, or delete files or folders, or to run programs.
database management system (DBMS) نظام إدارة قواعد البيانات
is an app that creates, maintains, and accesses database systems. Popular DBMS' include MySQL, Oracle Database, and Microsoft Access. Common database operations include: Adding new data Editing existing data Deleting data Querying (الاستعلام)the database for information. A query is a search in a database for data.
audio file
is basically a series of numbers of sampled audio voltages, along with the sampling rate.
Information
is processed data and gives meaning to the facts and values. Ex: 35, 39, 40 are the number of sweaters sold by a store over the last three weeks
Lossless compression
loses no information, so that decompression yields an identical file to the original. LZ and Huffman approaches are lossless. loses some information, so the decompressed file is close but not identical to the original. An example lossy compression approach is rounding. Ex: Given an original file containing 255, 64, 231, the one's place can be dropped (a form of rounding), yielding 25, 6, 23. A decompressor, knowing of the rounding but not knowing what numbers were dropped, may append 5's, yielding 255, 65, and 235, which is close but not identical to the original. Lossy compression may be OK for data like images or audio where humans barely notice a quality difference, but is clearly not OK for precise data like text or bank account numbers since the meaning would change.
automated backup system
makes regular backups of a user's files, either as the files are updated, or on a schedule like daily or weekly. Ex: Apple's Time Machine, Google Drive, and Dropbox. For the common case of a user accidentally deleting a needed file, many operating systems don't really delete the file from the drive, but rather move the file to a special folder called trash or a recycle bin. The user can thus recover an item from the trash. Every so often, a user may need to empty the trash, to free up space on a drive.
analog signal
meaning the signal changes continuously over time, like a flowing river. Because computers can only store 0's and 1's, a computer records audio as a digital signal, meaning as a series of numbers—digital means countable like a hand's fingers (fingers are also known as "digits", hence the word "digital"). A microphone converts vibrating air into an analog electrical voltage on a wire. An audio recording app may then rapidly "sample" that voltage (44,100 samples/second is common for music), using hardware called an analog-to-digital converter to convert each sample to a number, and storing the numbers in a file
Streaming تدفق
means to play video directly from the Internet (such as from YouTube, Netflix, etc.), using a web browser or other app, without ever storing the video as a file on a device. Streamed video is viewable immediately but requires a good Internet connection. Stored video can be viewed with a weak Internet connection or when offline entirely, and sometimes may be higher-quality video. Purchased videos that are stored rather than streamed, such as when purchased from an app like iTunes, often include additional features known as digital rights management (DRM), to discourage unauthorized copying.
text file ملف نصي
only stores text without any formatting information, and typically has a filename extension like myfile.txt. Simple apps like Notepad (for Windows) or TextEdit (for Macs) can edit text files. Beyond formatting, a modern word processor also supports insertion of drawings and images.
Audio
or sound, is the vibration of air molecules that human ears can detect
Most operating systems provide
provide some way for a user see what folder/file/app items exist on a drive, as well as to move, delete, or create new items, or to find items whose name or contents match certain words. For example, Mac OS X and Windows both show some file/folder/app items on the OS's main graphical view known as the desktop. Mac OS X provides an application named Finder Windows provides Windows Explorer, for users to manage folder/file/app items. iOS (for Apple smartphones and tablets) is somewhat unique by only showing apps, letting each app manage the app's own folders/files.
video player app
reads a video file, decompresses, and displays frames at the appropriate rate. Most modern devices have a built-in video player app, such as Quicktime on Mac and iOS devices or Windows Media Player for Windows devices. A video player app can sometimes save a video file in different formats, such as MOV or MP4. A video player app usually doesn't support all video file types. Some users choose to download video player apps rather than use a built-in app, with numerous apps available in app stores. The free VLC app is a popular download for Mac and WIndows machines due to supporting nearly all common video file formats.
Compression ضغط
reduces the size of a file. Ex: An image/photo file may be 4 megabytes before compression, but only 1 megabyte after. Compression enables a user to store more files on a drive. Compression also speeds up transfers of files via the Internet. Compression can be applied to any file, but is commonly applied to audio, image, and video files because such files are naturally large. Most apps for such files automatically compress and decompress those files.
Formatted text نص منسق
refers to features of a document like margins, text size, bold text, italicized text, colors, number of columns, etc. Popular word processors include Microsoft Word and Google Docs. A word processor creates a file that stores text plus formatting information, typically using a special filename extension like myfile.docx for Microsoft Word.
Data integrity النزاهة
refers to the accuracy of the data in the database.
A font's size
refers to the maximum height of any character. Font size is typically expressed in points (abbreviated pt), where a point is 1/72 of an inch. The most common font sizes for documents (like a cover letter, resume, book, etc.) is about 12 pt. Titles or headings (as in a book) are typically larger, such as 14 pt. A footnote might be 8 pt. A word processor user typically sets a document's normal font and font size, which applies to the entire document. The user can change the font or size of specific text in the document too. Word processing apps usually have icons for common features. Some examples are shown below (from a 2015 version of the Google Docs app), with short descriptions below each icon.
Digital video
stores each image as rows and columns of colored dots, each dot known as a picture element or pixel. Standard video uses about 24 frames per second, and each image has 525 pixel rows (known as lines). Compared to standard video, high-definition video uses more frames per second (like 60) and more lines (like 1080), as well as wider lines.
multitasking تعدد المهام OS
supports running multiple applications seemingly simultaneously, akin to a chef stirring the sauce a bit, then shaking a frying pan a bit, then stirring again, then shaking again, etc. To a user, multiple applications like a music player and a web browser appear to be running simultaneously, but in fact the OS is running a little bit of each application at a time, switching thousands of times per second.
PDF (portable document format) (تنسيق مستند محمول)
t) is a file format for storing documents (typically formatted text, images, and drawings) independently of any particular editing app like a word processor. A file that is useful across different applications, computers, or operating systems is said to be portable. PDF: was originally created by a company called Adobe Systems and published in 1993; PDF was initially proprietary but as of 2008 became freely usable. Prior to PDF, a document created using one app like Microsoft Word, Adobe Illustrator, etc., could not be viewed on or printed from a computer that didn't have that same app. PDF viewing apps are common and usually free and thus included on nearly device today.
Presentation tools display
the completed slideshow. A computer is typically connected to a projector to display the final slideshow. Mouse clicks or keyboard commands advance the slides and animation effects. Presentation tools often provide additional tools to users. Controls on the computer enable a users to jump to a particular slide, exit presentation mode, among others. Speakers can annotate slides in the editing tools, then display the notes during the slideshow. Presentation tools are not visible to audience members.
MS DOS
was introduced in 1981 by Microsoft as a relatively simply OS for PCs, which were new at that time. MS DOS was text based.