21-11-2012, 01:58 PM
Presentation on COMPUTER SYSTEM OVERVIEW
COMPUTER.ppt (Size: 656 KB / Downloads: 27)
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
Processor
Controls operation, performs data processing
Two internal registers
Memory address resister (MAR)
Memory buffer register (MBR)
I/O address register
I/O buffer register
Main Memory
Volatile
Data is typically lost when power is removed
Referred to as real memory or primary memory
Consists of a set of locations defined by sequentially numbers addresses
Containing either data or instructions
Processor Register
Faster and smaller than main memory
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
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
Multiprogramming
Processor has more than one program to execute
The sequence the programs are executed depend on their relative priority and whether they are waiting for I/O
After an interrupt handler completes, control may not return to the program that was executing at the time of the interrupt
Cache Memory
Invisible to the OS
Interacts with other memory management hardware
Processor must access memory at least once per instruction cycle
Processor speed faster than memory access speed
Exploit the principle of locality with a small fast memory
Direct Memory Access
Performed by a separate module on the system
When needing to read/write processor issues a command to DMA module with:
Whether a read or write is requested
The address of the I/O device involved
The starting location in memory to read/write
The number of words to be read/written
Evolution of Operating Systems
It may be easier to understand the key requirements of an OS by considering the evolution of Operating Systems
Stages include
Serial Processing
Simple Batch Systems
Multiprogrammed batch systems
Time Sharing Systems