Computer System Structure

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Computer System Structure af Mind Map: Computer System Structure

1. Computer System Architecture

2. Computer-System Operation

2.1. Computer system consists of one or more CPUs and a number of device controllers.

2.2. A Each device controller is in charge of a specific type of device

2.2.1. Has local Buffer

2.2.2. Iinforms CPU that it has finished its operation by causing an interrupt

3. Interrupt Handling

3.1. When the CPU is interrupted, it stops what it is doing and immediately transfers execution to a fixed location.

3.1.1. The fixed location contains the starting address of the interrupt service routine

3.2. Interrupt vector provide the address of the interrupt service routine

3.3. storing registers and the program counter.

4. Synchronous I/O Structure

4.1. Wait instruction idles the CPU until the next interrupt

4.2. Wait loop

4.3. no simultaneous I/O processing.

5. Asynchronous I/O Structure

5.1. After I/O starts, control returns to user program without waiting for I/O completion.

5.1.1. System call

5.1.2. Device-status table

5.1.3. determine device status and to modify table entry to include interrupt.

6. Two I/O Methods

7. Storage Structure

7.1. Main memory

7.1.1. only large storage media that the CPU can access directly.

7.1.2. volatile storage device

7.1.3. loses its contents when power is turned off.

7.2. Secondary storage

7.2.1. nonvolatile storage capacity

7.2.2. hold large quantities of data permanently

8. Storage Hierarchy

8.1. Storage systems organized in hierarchy.

8.1.1. Speed

8.1.2. Cost

8.1.3. Volatility

8.2. Caching

8.2.1. copying information into faster storage system

8.2.2. main memory last cache for secondary storage

9. Storage Device Hierarchy

10. Caching

10.1. Migration of A From Disk to Register

11. Modes of Operation

11.1. User Mode

11.1.1. user program executes in user mode

11.1.2. certain areas of memory are protected from user access

11.1.3. certain instructions may not be executed

11.2. Kernel Mode

11.2.1. monitor executes in kernel mode

11.2.2. privileged instructions may be executed

11.2.3. protected areas of memory may be accessed

12. Dual-Mode Operation

12.1. distinguish between the execution of operating system code and userdefined code.

12.2. Provide hardware support to differentiate between at least two modes of operations.

13. Dual-Mode Operation

13.1. Mode bit is added to computer hardware to indicate the current mode: kernel (0) or user (1

13.2. When an interrupt or fault occurs, hardware switches to kernel mode.

13.2.1. the software has complete control of the processor and all instruction, registers and memory

13.3. Privileged instructions can be issued only in monitor mode

14. I/O Protection

14.1. User program must executes a system call to request that the operating system to perform I/O.

15. Use of A System Call to Perform I/O

16. Memory Protection

16.1. protection at least for the interrupt vector and the interrupt service routines.

16.2. two registers are used to determine the range of legal addresses a program may access:

16.2.1. Base register – holds the smallest legal physical memory addres

16.2.2. Limit register – contains the size of the range

17. Use of A Base and Limit Register

18. Hardware Address Protection

19. Hardware Address Protection

19.1. When executing in kernel mode, the operating system has unrestricted access to both monitor and user’s memory

19.1.1. Operating system is allowed to load users’ programs into users’ memory access modify parameters of system calls.

20. CPU Protection

20.1. Timer – interrupts computer after specified period to ensure operating system maintains control over CPU

20.1.1. Every time the clock ticks, the counter is decremented

20.1.2. When timer reaches the value 0, an interrupt occurs.

20.2. control transfers to the operating system.

20.3. Load-timer is a privileged instruction