Chapter 2 Computer System Structures

Chapter 2 Computer System Structures

1. Computer-System Operation

   • Interrupt indicates the occurrence of an event from either the hardware of software

2. Interrupt Handling

   • Interrupt vector
     • Interrupt vector provide the address of the interrupt service routine
   • Interrupt service routine

3. Synchronous I/O Structure

   • After I/O start, control return to user program only upon I/O completion.
   • At most one I/O request is outstanding at a time,no simultaneous I/O processing

4. Asynchronous I/O Structure

   • After I/O start, control return to user program without waiting for I/O completion
   • Device-status table, contains entry for each I/O device indicating its type, address, and state

5. Computer System Architecture

   • Memory controller
     • To synchronize the access to memory

6. Storage Structure

   • Main memory
     • CPU can access directly
     • Volatile storage
   • Secondary storage
     • Nonvolatile storage

7. Storage Hierarchy

   • Storage system organized in hierarchy
     • speed
       • The higher Hierarchy more faster
     • cost
       • The higher Hierarchy more expensive
     • volatility
       • The higher Hierarchy more smaller storage capacity
   • Caching
     • Copying information into faster storage system

8. Dual-Mode Operation

   • The computer system must be able to distinguish between the execution of operating system code and use-defined code.
   • Modes of operation
     • User mode
     • Kernel mode
   • Mode bit
     • kernel (0)
     • user (1)

9. I/O Protection

   • All I/O instruction are privileged instruction

10. Memory Protection

    • The computer system may provide memory protection at least for the interrupt vector and interrupt service routine.
    • Memory outside the defined range is protected
    • Base register - holds the smallest legal physical memory address
    • Limit register - contains the size of range

11. The load instructions for the base and limit registers are privileged instruction

12. Timer - interrupts computer after specified period to ensure the operating system maintains control over CPU

13. Load-timer is a privileged instruction