COMPUTER SYSTEM STRUCTURES

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COMPUTER SYSTEM STRUCTURES by Mind Map: COMPUTER SYSTEM STRUCTURES

1. MODES OF OPERATION

1.1. KERNEL MODE

1.1.1. Monitor executes in kernel mode

1.1.2. privileged instructions may be executed

1.1.3. Protected areas of memory may be accessed

1.2. USER MODE

1.2.1. User program executes in use mode

1.2.2. Certain areas of memory are protected from user access

1.2.3. Certain instructions may not be executed

2. I/O STRUCTURE

2.1. Synchronous I/O Structure

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

2.1.1.1. Wait instruction idles the CPU until the next interrupt.

2.1.1.2. Wait loop (contention for memory access).

2.1.1.3. At most one I/O request is outstanding at a time, no simultaneous I/O processing.

2.2. Asynchronous I/O Structure

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

2.2.1.1. System call – request to the operating system to allow user to wait for I/O completion.

2.2.1.2. Device-status table contains entry for each I/O device indicating its type, address, and state.

2.2.1.3. Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt.