computer systems 2010-2011 week 10: file organisation alma whitfield
TRANSCRIPT
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Previously covered Components of a Computer System How a program in main memory is
executed making use of input and output devices connecting with other computers
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This Week See how programs and data are
permanently stored on a computer system
Organise files using the Windows Explorer Graphical User Interface
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Recap The CPU processes instructions Before this can happen the
Instructions need to be fetched from main memory (RAM)
Compared with the hundreds/thousands of applications on your computer RAM is small e.g. 2 GB of RAM 400 GB of hard disk (1 GB = 1 gigabyte = 1,000 million bytes)
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Recap When you switch off the computer
the contents of RAM are lost Where does RAM get its data from?
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Files The instructions and data are
organised into files stored on secondary storage such as a hard disk
A file can be described as a named collection of bytes representing instructions or data
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Secondary Storage Secondary Storage is effectively a
huge data structure for storing files
Data structures include Tables, Pointers and Linked Lists (more on this in SPS after Christmas)
How the data structure organises and stores the data is dependent on the type of Table, Pointers and Linked List being used
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File names Early PCs
File names restricted to 8 characters maximum followed by up to 3 characters after a full stop
e.g. FileOrga.doc Modern PCs
File names can be any length up to 256 characters
Can include spaces e.g. FileOrganisation.doc
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Files and Secondary Storage Devices such as hard disc and CDs,
DVDs and pen drives can store files permanently i.e. even when the device is switched off these devices are referred to as
secondary storage
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Data files Bytes represent text, pictures,
sounds, movies The files can be opened or played
or edited by appropriate programs e.g. Notepad program for text files e.g. Word program for Word document
files e.g. Windows Media Player program for
video and audio files e.g. Data processing programs for
customer record files
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Program files Bytes represent instructions Two main varieties of program file
exe files – bytes are machine code instructions (as in 3-Bit)
batch files – bytes are text containing operating system commands
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Program files1. Application Programs:
Microsoft word Internet Explorer etc.
2. System Programs: operating systems like Windows or
Linux language translators such as Java,
Pascal, C, C++ that translate high level language programs into machine code
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Source code files Bytes represent text (they can be
regarded also as text files) The text is human-readable program
instructions e.g. written in Java before they get translated into machine code by compilers
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Organising files Thousands of files can be held in
secondary storage Organising the files is a job for the
operating system
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Operating System and Files Q. When you double click on a file,
how does the Operating System know what to do with that file?
A. Filename extensions (also known as file extensions for short)
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File Extensions Files have names
They also have something else called extensions (the letters that follow the last dot (.) in a file’s name.
The extension reveals the type of each file e.g. cars.jpg, (this is an image extension)
sales1.doc (this is a Microsoft Word document)
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For example The following extensions indicate
that the data contained within the file is executable .exe .com .bat .cmd
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Saving data from Applications When you save data from an
application the application will usually automatically tag on the extension .doc .ppt .mdb .txt
You could also tell the application to save as a different file type such as .htm
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File Attributes Files have attributes associated
with them. An attribute is another word for a
charactistic For example you could make a file
READ-ONLY, HIDDEN, ARCHIVE
Right Mouse click and select properties on the file to set these attributes
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Operations on Files Create a file / Delete a file Open a file / Close a file Read data from a file Write data to a file Reposition the current file pointer in a file Append data to the end of a file Truncate a file (delete part of its
contents) Rename a file Copy a file
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Using the PC Filing System PCs running popular operating systems such
as Windows and Linux organise computer files into directories (sometimes called folders) on your secondary storage (e.g. hard drive).
These directories are based on a hierarchical structure, where the root directory (denoted by \ ) is at the top of that structure.
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Directory Trees A directory of files can be contained
within another directoryThe directory containing another is usually called the parent directory, and the one inside is called a subdirectory
Directory tree A logical view of a file system; a structure showing the nested directory organization of a file system
Root directory The directory at the highest level
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The file directory
A directory is a table listing files and their location on the disc
Directories are called folders in Windows
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The file directory
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In practice, the black blobs are numbers giving the addresses of the locations of the files on the disc surface
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Directory entries can be other directories leading to ...
... a hierarchical directory structure
i.e. folders within folders
i.e. a tree data structure
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File Handling in Microsoft Windows Microsoft windows is based on a graphical
user interface (GUI). This makes handling files and directories simple.
Using Windows Explorer you can: Find files and folders Copy files and folders Move files and folders Delete files and folders Create folders
Demo ... more in the seminar