mov 0x8049cd4, %eax # load balance
add $0x1, %eax      # add
mov %eax, 0x8049cd4 # store

Problem: Each thread (t1, t2) will run through the above 
code sequence once; what is the final value of counter?
(how many different final values are possible?)

Thread 1              Thread 2             %eax  balance
--------              --------             ----  -------
                                             0     100
mov 0x8049cd4, %eax                        100     100
add $0x1, %eax                             101     100
mov %eax, 0x8049cd4                        101     101
*** INTERRUPT *** (context switch)           0     101
                      mov 0x8049cd4, %eax  101     101 
                      add $0x1, %eax       102     101
                      mov %eax, 0x8049cd4  102     102 **

TRY #2:
                                             0     100
mov 0x8049cd4, %eax                        100     100
add $0x1, %eax                             101     100
*** INTERRUPT *** (context switch)           0     100
                      mov 0x8049cd4, %eax  100     100
                      add $0x1, %eax       101     100
                      mov %eax, 0x8049cd4  101     101 
*** INTERRUPT *** (context switch)         101     101
mov %eax, 0x8049cd4                        101     101