Summary Operating system AS level Computer Science
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Module
Computer Science
Institution
Computer Science
Book
Cambridge International AS & A Level Computer Science
Simple and neat notes on Operating system topic AS level Computer Science. Notes are based on Hodder education AS/A level Computer Science book and cover all components that may come in the exam.
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Operating system
The need for an Operating system
● Operating system – software that provides an environment in which applications
can run and provides an interface between hardware and human operators.
● In modern computers, the BIOS contents are stored on a flash memory chip. The
BIOS configuration is stored in CMOS memory (complementary metal-oxide
semiconductor) which means it can be altered or deleted as required.
● The required part of the OS is copied to RAM. The OS is very large, so it affects
the computer's performance if it was loaded to RAM all at once.
● An operating system provides both the environment in which applications can be
run, and a usable interface between humans and computers. An operating
system also disguises the complexity of computer hardware.
● The human–computer interface (HCI) is usually achieved through
○ Command line interface (CLI)
■ requires a user to type instructions to choose options from menus
■ has to learn a number of commands to carry out basic operations
■ it takes time to key in commands every time an operation has to be
carried out
■ the user is in direct communication with the computer
■ is not restricted to a number of predetermined options
○ Graphical user interface (CLI)
, 2
■ Allows the user interact with a computer using pictures or symbols
(icons)
■ windows, icons, menu and pointing device (WIMP)
■ A windows manager looks after the interaction between windows,
the applications and windowing system
■ Smart phones, tablets and many computers now use post-WIMP
● Allows actions such as pinching and rotating
Operating system tasks
Memory management
● management of the computer's main memory.
○ Memory optimisation
■ Allocation and deallocation of memory when several applications
are running simultaneously
■ It also determines where they are stored in memory
■ Must keep track of all allocated memory and free memory
■ To maintain optimisation, it also swap data to and from HDD and
SSD
○ Memory organisation
■ Determines how much memory is allocated to an application
■ How the memory can be split up in the most appropriate and
efficient way
■ Ways to do so:
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