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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 1
Today’s class
Finish computer system overview Review of more C
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Finish computer system overview
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 3
Instruction Execution
Two steps Processor reads (fetches) instructions from
memory Processor executes each instruction
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 4
Instruction Cycle
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 5
Instruction Fetch and Execute
Program counter (PC) holds address of the instruction to be fetched next
The processor fetches the instruction from that memory location
Program counter is incremented after each fetch
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 6
Instruction Register Fetched instruction is placed in the instruction
register Categories
Processor-memory Transfer data between processor and memory
Processor-I/O Data transferred to or from a peripheral device
Data processing Arithmetic or logic operation on data
Control Alter sequence of execution
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 7
Characteristics of a Hypothetical Machine
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 8
Example of Program Execution
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 9
Direct Memory Access (DMA)
I/O exchanges occur directly with memory Processor grants I/O module authority to
read from or write to memory Relieves the processor of the
responsibility for the exchange
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 10
Interrupts
Interrupt the normal sequencing of the processor
Most I/O devices are slower than the processor Processor must pause to wait for device
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 11
Classes of Interrupts
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 12
Program Flow of Control Without Interrupts
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 13
Program Flow of Control With Interrupts, Short I/O Wait
UserProgram
WRITE
WRITE
WRITE
I/OProgram
I/OCommand
InterruptHandler
END
1
2a
2b
3a
3b
4
5
(b) Interrupts; short I/O wait
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 14
Program Flow of Control With Interrupts; Long I/O Wait
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 15
Interrupt Handler
Program to service a particular I/O device Generally part of the operating system
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 16
Interrupts
Suspends the normal sequence of execution
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 17
Interrupt Cycle
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 18
Interrupt Cycle
Processor checks for interrupts If no interrupts fetch the next instruction
for the current program If an interrupt is pending, suspend
execution of the current program, and execute the interrupt-handler routine
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 19
Timing Diagram Based on Short I/O Wait
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 20
Timing Diagram Based on Long I/O Wait
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 21
Simple Interrupt Processing
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 22
Multiple Interrupts Disable interrupts while an interrupt is
being processed
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 23
Multiple Interrupts Define priorities for interrupts
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 24
Multiple Interrupts
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 25
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
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 26
Memory
Faster access time, greater cost per byte Greater capacity, smaller cost per byte Greater capacity, slower access speed
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 27
Memory Hierarchy
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 28
Going Down the Hierarchy
Decreasing cost per byte Increasing capacity Increasing access time Decreasing frequency of access of the
memory by the processor Locality of reference
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 29
Secondary Memory
Nonvolatile Auxiliary memory Used to store program and data files
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 30
Disk Cache
A portion of main memory used as a buffer to temporarily to hold data for the disk
Disk writes are clustered Some data written out may be referenced
again. The data are retrieved rapidly from the software cache instead of slowly from disk
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 31
Cache Memory
Invisible to operating system Increase the speed of memory Processor speed is faster than memory
speed Exploit the principle of locality
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 32
Cache Memory
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 33
Cache Memory
Contains a copy of a portion of main memory
Processor first checks cache If not found in cache, the block of memory
containing the needed information is moved to the cache and delivered to the processor
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 34
Cache Read Operation
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 35
Cache Data Modified
Write policy dictates when the memory write operation takes place Can occur every time cache block is updated Can occur only when cache block is replaced
Minimizes memory write operations Leaves main memory in an obsolete state
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 36
I/O Communication Techniques
Programmed I/O Interrupt-driven I/O Direct memory access (DMA)
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 37
Programmed I/O I/O module performs the
action, not the processor Sets appropriate bits in the I/O
status register No interrupts occur Processor checks status until
operation is complete
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 38
Interrupt-Driven I/O Processor is interrupted when I/O
module ready to exchange data Processor saves context of
program executing and begins executing interrupt-handler
No needless waiting Consumes a lot of processor time
because every word read or written passes through the processor
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 39
Direct Memory Access Transfers a block of data
directly to or from memory An interrupt is sent when the
transfer is complete Processor continues with
other work
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Review of more C
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 41
Structures Equivalent of Java’s classes with only data (no
methods)Example 6:#include <stdio.h>
struct birthday{ int month; int day; int year; }; //Note the semi-colon
int main() { struct birthday mybday; /* - no ‘new’ needed ! */ /* then, it’s just like Java ! */ mybday.day=1; mybday.month=1; mybday.year=1977; printf(“I was born on %d/%d/%d”, mybday.day, mybday.month, mybday.year);}
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 42
More on structuresstruct person{ char name[41]; int age; float height; struct { /* embedded structure */ int month; int day; int year; } birth; };
struct person me;me.birth.year=1977;………
struct person class[60]; /* array of info about everyone in class */
class[0].name=“Gun”; class[0].birth.year=1971;……
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 43
typedef typedef struct person myPerson
Defines a new type name myPerson as a synonym for type struct person
int main(){myPerson me;me.age = 6; …
}
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 44
User-defined header files Structures and other data structures may
be defined in a header file, for better organization of the code
These are user-defined header files e.g. person.h
To include it:#include “person.h”
at the start of the program file
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 45
Command line arguments
Accept inputs through the command line. main(int argc, char* argv[])
argc – argument countargv[] – value of each argument
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Thursday, September 6, 2007
Computer Systems/Operating Systems - Class 2 46
Example 7#include <stdio.h>
intmain(int argc, char *argv[]){ int count = 0; if(argc < 2){ printf("Must enter at least one argument\n"); printf("Example: ./a.out this is program 7\n"); exit(1); } printf(" The number of arguments is %d\n", argc); printf("And they are :\n"); while(count < argc){ printf("argv[%d]: %s\n",count,argv[count] ); count++; } printf("\n"); return 0;}