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OPERATING SYSTEMS 2 - OVERVIEW
PIETER HARTEL
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Operating System
 Resource manager
 Hardware resources
 Resources provided by the OS itself (which?)
 Objectives
 Convenience (why?)
 Efficiency (why?)
 Evolvability (why?)
 Abstraction is the key to managing the complexity
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History
 Batch
 Time sharing
 Real-time
 Multi-processor
 Distributed systems
Electrologica X8 console, 1965
 Multi-core (why?)
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Concepts and abstractions
Concept
Abstraction of
 Processes & Threads
 Processor
 Memory management
 Physical memory & disks
 Protection and security
 Dedicated computer
 Scheduling and resource
management
 Dedicated computer
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Abstraction layers
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Linux example of the Unix API
 Output?
 gcc Echo.c
 ./a.out Hello world
 strace ./a.out Hello World
#include <stdio.h>
int main(int argc, char *argv[]) {
int i;
for(i=0; I < argc; i++) {
printf("%s ", argv[i]);
}
printf("(%d)\n", argc);
return 0;
}
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Process abstraction
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Resource sharing (why?)
 Deadlock (why?)
 Prevention
 Detection
 Recovery
 Avoidance
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Process management
 Scheduling
 Timer
 Threads (why?)
Which process is
running?
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Address space management
text
main
etext
data
 ./a.out
edata
bss
b
extern char etext, edata, end;
int a = 0xaaaa, b;
int main(int argc, char * argv[]) {
int c = 0xcccc;
int *d_ptr = (int*) malloc(sizeof(int));
int *e_ptr = (int*) alloca(sizeof(int));
b = 0xbbbb;
*d_ptr = 0xdddd;
*e_ptr = 0xeeee;
printf("%p:a=%0x\n", &a, a); …
}
low
end
heap
heap
 gcc AddressSpace.c
a
d
brk
stack
 Output?
stack
e
argc
c
high
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Memory management
 Paging (why?)
 MMU!
 Swapping (why?)
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Protection and Security
 Processes vs the OS (how?)
 Processes vs other Processes (how?)
 Privileged processes (why?)
 Access control matrix
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I/O management
#include <stdio.h>
#include <unistd.h>
#define N 41
 Output?
 gcc Wrap.c
 strace ./a.out Wrap.c junk
 Find the system calls for:
 fgets()
 fputs()
int main(int argc, char * argv[]) {
if(argc >= 3) {
FILE *from = fopen(argv[1], "r");
FILE *to = fopen(argv[2], "w");
char buf[N];
while (fgets(buf,N,from) != NULL) {
fputs(buf,to); fputc('\n',to);
}
fclose(from);
fclose(to);
return 0;
} else {
printf("usage %s from to\n", argv[0]);
return 1;
}
}
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Virtual Machine management
 Examples?
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Summary
 Operating systems are large, hence abstraction to manage complexity:
 Processes and threads
 Memory
 Files and peripherals
 User accounts
 Management issues
 Fairness
 Sharing
 Protection
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