Address Spaces

• OS was a set of routines (a library) that sat in memory at address 0
• One running program
• Systems were simple!

Multiprogramming and Time Sharing

• Multiple processes were ready to run at a given time
• Multiple people sharing one system
• Time sharing the hardware
• Systems became interactive!

The Address Space

Virtualize Memory

• The OS must virtualize the memory
• All process can’t start at 0!
• But all process think they do?

Memory Quiz

In class exercise! For all the following slides you will be shown a snippet of code and will need to determine where the variable lives.

• Data
• Heap
• Stack

int *A;
 void foo(int* bar, int len){
     A = malloc(sizeof(int)*len);
     /*...some code*/
 }
 void main(int argc, char **argv){
     int length =10; int i; int bar[length];
     foo(&bar[0], length);
     /*...some code*/
     free(A);
 }

• Length
• bar (in foo)
• bar (in main)
• bar[0]
• argc
• *A (dereference A)