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What are the 2 main services and function provided by an OS?
- 1) System Service: Functions that enable the OS to operate properly to perform its duties/Used for the system itself/running on its own
- 2) Users Services: Allow user to interact with OS/Higher Level/for user
What are the services useful to the user?
User interface, Program execution , i/o operations, file system manipulations, communications, error detection
What are the services useful to the system?
- Resource allocation: Many types of resources, cpu cycles, main memory file storage
- Accounting: Keeps track of which users use how much and what kind of resources
- Protection and security: One process should not interfere with another. All access to system resources must be controlled.
What is a system call?
A system call is the main way a user program interacts with the OS. User program make use of system calls to request services provided by the OS
Give an example of system call?
Example system call sequence/ Acquire input file name/ write prompt to screen/ accept input/ Acquire output file name/ write prompt to screen/ accept input/ Open the input file/ if file does not exist abort Create output file/ If file exist abort/ Loop / read from input file/ write to output file/ Until read fails/ Close output file/ Write completion message to screen/ Terminate normally.
Describe the 6 main types of system calls?
Process control, File manipulation, Device manipulation, Information maintenance, Communications, Protection
What are the major activities of an OS with regard to file management?
- � Create & Delete file
- � Open & Close
- � Read, Write & Reposition
- � Get & Set file attributes.
What are the major activities of an OS with regard to device management?
- � Request & Release device
- � Read, Write & Reposition
- � Logically attach & detach devices
- � Get & Set device attributes
What are the major activities of an OS with regard to process control?
- � End & Abort
- � Load & Execute
- � Create & Terminate process
- � Wait for time
- � Allocate & Free memory
- � Get & Set process attributes
- Note: Process control is not the same as process managment
What are the major activities of an OS with regard to Information Maintenance?
- � Get & Set time or date
- � Get & Set system data
- � Get & Set process, file or device attributes
What are the major activities of an OS with regard to Communications?
- � Create & delete communication connection
- � Send & Receive messages
- � Transfer status information
- � Attach or detach remote devices
What are the major activities of an OS with regard to protection?
- � Mechanism for control of access to system resources
- � Get & Set Permission
- � Allow & Deny user
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