Computers4 Ch2
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Transcript of Computers4 Ch2
- 1. Operating Systemand Utility Programs Chapter 2 B.M.H
2. Computer System
- Hardware
- Input device
- Processor (CPU)
- Output device
- Storage (secondary storage)
- Software
- System SW
- Application SW
- People
MIU 3. Learning Objectives
- OS for large computer systems
- The method of resource allocation
- Utility Programs
MIU 4. Mainframes
- Large, fast and fairly expensive computers
- Used by business or governmentto provide centralized storage
- EX) IBM 4381, 9300, 3090, Cyber 180
MIU 5. MIU 6. OS for large computers
- Large computer - mainframes
- Around about twice as long as PCs
- Owned by businesses and universities
- Used by many people at once
- Present special (sharing) problems
- Program, CPU, memory, storage, printer
- OS : take care of these things behind the scenes
- So that User can share the computer s resources
MIU 7. Resource Allocation
- Allocated?
- Shared resources
- (Allocate : give something to somebody for special purpose)
- Resources allocation
- : the process of assigning computer resources to certain programs
MIU 8. Resource Allocation
- Sharinga CPU
- Sharinga Memory
- SharingStorage Resources
- SharingPrinting Resources
MIU 9. Sharing the CPU
- Most computers have a single CPU.
- All programs must share it.
- The sharing process
- Controlled by the OS
- Two approaches to sharing
- Multiprogramming
- Time-sharing
- Multiprocessing
MIU (Resource allocation) 10. Multiprocessing
- The use of a powerful computer withmultiple CPUs
- Multiple programs can runsimultaneously , each using its own processor
MIU (Resource allocation) 11. Multiprogramming
- Onlyone Central Processing Unit
- Two or more programs are executed in the same time frame,concurrently
- But not exactly at the same instant
- Taking turns ; one program runs for a while, and then another one runs
- Event-driven
- Programs share resources based on events that take place in the programs.
MIU (Resource allocation) 12. Multiprogramming
- Implemented by OS through a system of interrupts
- Interrupts
- A signal that causes normal program processing to be suspended temporarily.
MIU 13. Time-Sharing
- A special case of multiprogramming
- Time-driven
- To give each user a time slice
- The OS doesn t wait for completion of an event
- At the end of the time slice, the resources are taken away from the user and given to someone else
MIU (Resource allocation) 14. Sharing Memory
- Memory management
- The process of
- allocating memory to programs and
- keeping the programs in memory separate from one another
- Methods
- Partitions (or regions)
- Foreground and background
- Virtual storage
MIU (Resource allocation) 15. Partitions
- Some systems simply divide memory into separate areas (partitions or regions)
- Each of which can hold a program
MIU Sharing Memory 16. Foreground and Background
- Large all-purposed computers divide the memory into foreground and background
- In a time-sharing environment
- Foreground
- For programs that havehigher priority
- : Interactive program (with the user at a terminal awaiting response)
- Receive more CPU time
- Background
- For programs with less pressing schedules
- lower prioritiesand less CPU time
MIU Sharing Memory 17. Virtual Storage (1)
- Many computer systems uses this technique
- Calledvirtual memory
- Virtual : made to appear to exist by the use of computer SW
- The programs currently being executed are stored ondisk ,
- portions of these programs
- are brought intomemoryas needed.
- Memory : real storage
- Secondary storage : virtual storage
MIU Sharing Memory 18. Virtual Storage (2)
- Paging
- one way of virtual storage
- the process of
- dividing a program into equal-size pieces
- ; calledpages
- storing them in equal-size memory spaces
- ; calledpage frames
- All pages and page frames
- : the same fixed size (ex. 2 or 4 KB)
MIU Sharing Memory Refer to Fig 2-11 19. Sharing Storage Resources
- More than user want to read or write a record
- from the same disk pack at the same time
- OS
- Keeps track of which file is where
- Responds to commands to manipulate files
- Keeps track of the Input and output requests
- Processes them
- In the order in which they were received
- Routes any program instruction to read or write a record
MIU Resource allocation 20. Sharing Printing Resources
- Spooling
- A process for sharing a printer
- Moving data and store it for a short time on adiskbefore it is printed
- Each program writes onto a disk each line that is to be printed
- The disk file is placed into aqueue
- It is printed when the printer becomes available
MIU Resource allocation 21. Utility Programs File Manager Back up and Restore File Compression Defragmenter Device Drivers 22. Utility Programs (1)
- Most of the resource allocation tasks
- : done by the OS without user involvement
- Utility Programs
- : perform explicit servicesat the user s request
- Utility : a piece of computer SW that performs a particular task
- Part of the system software, not part of the OS.
- Some utilities are packaged with OSs
- Others can be purchased separately
MIU 23. Utility Programs (2)
- To avoid duplication of effort
- Backing up
- Restoring files
- Compressing files and entire hard disks
- Locating files
- Searching computer viruses
MIU 24. File manager (1)
- Organize and manage files in a hierarchical directory structure
- organized in a way that makes sense to you
- Directory
- : a named area in storage that can contain files and other directories
- The newer versions of Windows