CHAP1 - Computer System Overview Chapter 1 Operating System...

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Computer System Overview Chapter 1
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Operating System Exploits the hardware resources of one or more processors Provides a set of services to system users Manages secondary memory and I/O devices
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Basic Elements Processor Main Memory referred to as real memory or primary memory volatile I/O modules secondary memory devices communications equipment terminals System bus communication among processors, memory, and I/ O modules
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Top-Level Components
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Processor Registers User-visible registers Enable programmer to minimize main- memory references by optimizing register use Control and status registers Used by processor to control operating of the processor Used by operating-system routines to control the execution of programs
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User-Visible Registers May be referenced by machine language Available to all programs - application programs and system programs Types of registers Data Address Index Segment pointer Stack pointer
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User-Visible Registers Address Registers Index involves adding an index to a base value to get an address Segment pointer when memory is divided into segments, memory is referenced by a segment and an offset Stack pointer points to top of stack
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Control and Status Registers Program Counter (PC) Contains the address of an instruction to be fetched Instruction Register (IR) Contains the instruction most recently fetched Program Status Word (PSW) condition codes Interrupt enable/disable Supervisor/user mode
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Control and Status Registers Condition Codes or Flags Bits set by the processor hardware as a result of operations Can be accessed by a program but not altered Examples positive result negative result zero Overflow
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Instruction Cycle
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CHAP1 - Computer System Overview Chapter 1 Operating System...

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