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Computers, file size, units of measurement and storage devices



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During my teaching days ( I used to teach computer basics ) in 1999 / 2000, I made it a point to cover at least 1 lecture on units & measurements, file size and storage devices. The reason being many of my students were absolutely blank with regards to file size and the amount of data a floppy or a hard disk could store.

The basic unit used in computer data storage is called a bit (binary digit). Computers use these little bits, which are composed of ones and zeros, to do things and talk to other computers. All your files, for instance, are kept in the computer as binary files and translated into words and pictures by the software (which is also ones and zeros). This two number system, is called a “binary number system” since it has only two numbers in it. The decimal number system in contrast has ten unique digits, zero through nine.

Typical size of various computer files :

1. DOC files – 20 to 40 Kilobytes
2. IMAGE files – 20 to 200 kilobytes
3. MP3 files – 1000 to 4000 Kilobytes

The above sizes are theoretical and can exceed far more than mentioned.

A hard disk is measured in terms of Gigabytes and 3 1/2 inches floppy & Compact Disc in terms of Megabytes. These are 2 most commonly used storage devices apart from USB flash drives ( Storage capacity from 128 Megabytes to 10 Gigabytes ). If you are aware about the size of your file and the capacity of your storage device then it will become as much easier to know the amount of data that can be transferred to that device.

Computer – units of measurement

Computers – Bits & Bytes
bit BIT 0 or 1
byte B 8 bits
kilobyte (decimal) KB 1000 bytes
megabyte (decimal) MB 1000 kilobytes
gigabyte (decimal) GB 1000 megabytes
terabyte (decimal) TB 1000 gigabytes
petabyte (decimal) PB 1000 terabytes
exabyte (decimal) EB 1000 petabytes

PLEASE NOTE : Real calculation should be based on the the following parameters ( 1 KB = 1024 bytes, 1 MB = 1024 KB and so on ).


Handy file extensions which you should not forget if you are a computer user.


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File extension awareness can prevent you from downloading potentially dangerous files. It will also let you know which application is needed to open them. Read this article and it will help you in your day to day work.

File extensions are like surnames ( In real life scenario ) …. The name can be chosen by you during the time of saving the file. The extension is given to it by the application. The list below has the most frequently used file extension names. In reality there are atleast a thousand file extensions existing as of today. So go through this list slowly.

SAMPLE : filename.extension

1. Text files – .txt
2. Documents / Word file – .doc
3. Microsoft Excel – .xls
4. Microsoft Access – .mdb
5. Microsoft Power Point – .ppt

Office 2007 has new file extensions. The 2007 Microsoft Office system introduces a new file format that is based on XML. It is called Open XML Formats. Word

XML file type Extension
Document .docx
Macro-enabled document .docm
Template .dotx
Macro-enabled template .dotm

Word supports a DOCX format (macro-free document) and a DOCM format (document that allows macros). Administrators can control the use of these formats by Group Policy.


XML file type Extension
Workbook .xlsx
Macro-enabled workbook .xlsm
Template .xltx
Macro-enabled template .xltm
Non-XML binary workbook .xlsb
Macro-enabled add-in .xlam


XML file type Extension
Presentation .pptx
Macro-enabled presentation .pptm
Template .potx
Macro-enabled template .potm
Macro-enabled add-in .ppam
Show .ppsx
Macro-enabled show .ppsm
Slide .sldx
Macro-enabled slide .sldm
Office theme .thmx

Compatibilty pack which is available from microsoft site can be used for opening/editing office 2007 files with older versions. Here is the link

6. Images – .jpeg, .gif, .png
7. Audio – .wav, .cda, .mp3 ( and other versions ), .wma etc
8. Video – .mpeg, avi(audio video interleave), .dat(VCD video file), DivX (DivX encoded movie), .m(real media)
9. Installers/ Executable – .exe
10. Corel Draw – .cdr
11. True type fonts ( Windows ) – .ttf
12. Webpage – .htm, .html, .xhtml
13. Programmed webpage – .php, .aspx, .cfm
14. Microsoft ebook reader – .lit
15. Rich Text File – .rtf
16. Photoshop – .psd
17. Flash – .flv, .fla
18. Zipped – .zip, .rar
19. Icons ( Windows ) – .ico
20. Outlook Express email – .dbx

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