Chapter 1 "Computer system overview". After studying this chapter, you should be able to: Describe the basic elements of a computer system and their interrelationship, eplain the steps taken by a processor to execute an instruction, understand the concept of interrupts and how and why a processor uses interrupts,. | Chapter 1 Computer System Overview Patricia Roy Manatee Community College, Venice, FL ©2008, Prentice Hall Operating Systems: Internals and Design Principles, 6/E William Stallings 1 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 2 Basic Elements Processor Two internal registers Memory address resister (MAR) Specifies the address for the next read or write Memory buffer register (MBR) Contains data written into memory or receives data read from memory 3 Basic Elements Processor I/O address register I/O buffer register 4 Basic Elements Main Memory Volatile Referred to as real memory or primary memory 5 Basic Elements I/O Modules Secondary Memory Devices Communications equipment Terminals System bus Communication among processors, main memory, and I/O modules 6 Computer Components: Top-Level View 7 Processor Registers User-visible registers Enable programmer to minimize main | Chapter 1 Computer System Overview Patricia Roy Manatee Community College, Venice, FL ©2008, Prentice Hall Operating Systems: Internals and Design Principles, 6/E William Stallings 1 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 2 Basic Elements Processor Two internal registers Memory address resister (MAR) Specifies the address for the next read or write Memory buffer register (MBR) Contains data written into memory or receives data read from memory 3 Basic Elements Processor I/O address register I/O buffer register 4 Basic Elements Main Memory Volatile Referred to as real memory or primary memory 5 Basic Elements I/O Modules Secondary Memory Devices Communications equipment Terminals System bus Communication among processors, main memory, and I/O modules 6 Computer Components: Top-Level View 7 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 privileged OS routines to control the execution of programs 8 User-Visible Registers May be referenced by machine language Available to all programs – application programs and system programs 9 User-Visible Registers Data Address Index register: Adding an index to a base value to get the effective 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 10 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) Contains status information 11 Control and Status Registers Condition codes or flags Bits set by processor hardware as a result of operations Example Positive, negative, zero, or overflow result 12 Instruction
