Computer System Structures

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Computer System Structures by Mind Map: Computer System Structures

1. I/O Structures

1.1. Synchronous I/O Structure

1.1.1. After I/O starts, control returns to user program only upon I/O completion.

1.2. Asynchronous I/O Structure

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

2. Storage Structure

2.1. Main memory

2.1.1. Only large storage media that the CPU can access directly.

2.2. Secondary storage

2.2.1. extension of main memory that provides nonvolatile storage capacity.

3. Storage Hierarchy

3.1. Storage systems organized in hierarchy.

3.1.1. Cost

3.1.2. Speed

3.1.3. Volatility

3.2. Caching

3.2.1. copying information into faster storage system; main memory can be viewed as a last cache for secondary storage

4. I/O Protection

4.1. Must ensure that a user program could never gain control of the computer in monitor mode (i.e., a user program, as part of its execution, stores a new address in the interrupt vector).

5. Memory Protection

5.1. Base register

5.1.1. holds the smallest legal physical memory address

5.2. Limit register

5.2.1. contains the size of the range

6. CPU Protection

6.1. Timer

6.1.1. interrupts computer after specified period to ensure operating system maintains control over CPU.

6.2. Load-timer is a privileged instruction

7. Dual-Mode Operation

7.1. Modes of Operation

7.1.1. User Mode

7.1.1.1. user program executes in user mode

7.1.1.2. certain areas of memory are protected from user access

7.1.1.3. certain instructions may not be executed

7.1.2. Kernel Mode

7.1.2.1. monitor executes in kernel mode

7.1.2.2. privileged instructions may be executed

7.1.2.3. protected areas of memory may be accessed

8. Interrupt Handling

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

8.2. Interrupt vector provide the address of the interrupt service routine for the interrupting device.

8.3. After the interrupt is serviced, the saved return address is loaded into the program counter.

9. Computer-System Operation

9.1. A general-purpose computer system consists of one or more CPUs and a number of device controllers.

9.2. The CPU and device controllers can execute concurrently

9.3. Device controller informs CPU that it has finished its operation by causing an interrupt.