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- 1Why is data represented in binary?- There are only two digits, 1 and 0 , used in binary reflect the on and off states of a transistor.
- The computer can process binary faster than other data types. - 2User Interface Software- The user interface is the boundary between the human user and the machine.
- Allows user to interact with the computer
- The interface:
1. Lets the user give commands
2. Asks questions
3. Displays a response - 3Memory Management- When an OS decides where to store data in the memory they have to make sure:
1. Memory is used efficiently
2. Important data isn't overwritten during the running of the program
- Memory is divided into pages, the process will be loaded into a vacant page.
- The OS keeps track of this and protects it from being overwritten by other processes. - 4Peripheral Management- A file is a named store of data on a secondary storage medium.
- Files can be:
1. Data files, such as a word processed document or database
2. Program files, such as OS components or applications
3. Configuration data, such as parts of the window registry
- When you save a file, the OS looks up where there is free space on the medium.
It writes the data to the medium and makes a record of where it is located so when you need the file next the OS looks up its location and retrieves it. - 5Multitasking- When the program is being executed, it is called a process.
- In many cases, it seems to the user that the processes are running at the same time ... this is called multitasking.
- For example, we can carry on with our work while a document prints or a file is being downloaded from the internet. In reality, these things do not happen at the same time.
- The OS shifts its attention between processes. - 6Multi-programming- Most all purpose systems commonly have several programs loaded into memory at the same time. This is called multi-programming.
- A multi-programming OS must:
1. Make sure the CPU is in use as much of the time as possible
2. Try to speed up the operation of all tasks
3. Share resources fairly between tasks - 7Multi-programming / Multitasking Policy- Shortest job first
- Round robin - all jobs get equal time
- First come first served
- Priorities - some jobs are more important than others, for example, when the user is making inputs, a virus scan might be relegated to a background task - 8Security: Authentication- OS's usually allow the authentication of users. This means they can be set up to check that users are who they say they are.
- This normally involves users having:
1. A user id: this checks who they are and what privileges they have
2. A password: this confirms that they really are, who they say they are - 9Security: Privileges- Privileges are the rights assigned to users and groups.
- They may include features such as:
1. Read (view it)
2. Write (change it)
3. Execute (run if it is a program) - 10Security: Encryption- Some files are encrypted. That is that they are transformed in such a way that an unauthorized person cannot understand them.
- 11Fragmentation- Secondary storage is divided into segments.
- Files are often larger then the size of the segment. So, files are usually split into blocks across many segments.
- If a file is split across many locations, it takes longer to read and write it.
- Each block contains Pointers. The OS will follow the Pointers to recover the whole file. (Fragmentation) - 12Defragmentation- After a while, access to the files on a computer begin to slow down.
- A process called defragmentation can they be used to tidy up the disk or other medium so that parts of the files are moved to be stored next to each other. - 13Nibble, Byte, Kilobyte, Megabyte, Gigabyte, Terabyte- Byte = 8 Bits
- Kilobyte = 1024 Bytes
- Megabyte = 1024 Kilobytes
- Gigabyte = 1024 Megabytes
- Terabyte = 1024 Gigabytes - 14Character Set- A complete collection of characters is a character set.
- Every word is made up of symbols or characters. When you press a key on a keyboard, a number is generated that represents the symbol for that key. - 15ASCII- The ASCII character set is a 7-bit set of codes that allows 128 different characters
- That is enough for every upper-case letter, lower-case letter, digit and punctuation mark on most keyboards.
- ASCII is only used for the English language. - 16Extended ASCII- Extended ASCII code is an 8-bit character set that represents 256 different characters, making it possible to use characters such as é or ©.
- Extended ASCII is useful for European languages. - 17Unicode- Unicode uses between 8 and 32 bits per character, so it can represent characters from languages from all around the world.
- As it is larger than ASCII, it might take up more storage space when saving documents. - 18—
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- FlashCards sobre Sem título, criado por Alfie Hann em 31-05-2017.
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- Alfie Hann
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