58123-3 Computer Systems Organisation (Open University)

Exam  27.8.1999

1. Answer shortly the following questions.
a) What is a cache? Why is it used? Where is it used? (3 p)
b) What is a semaphore used for? What connection does the semaphore 
   have to  processes?  Give an example of the use of the semaphore. (3 p)
c) For what purpose is a compiler used? How and for what purposes do 
   compilers use  the symbol table? (2 p)
d) For what purpose is a device controller used? What tasks has 
   a device driver? (2 p)
e) What  factors  make RISC machines fast and effective? (3 p)   

2. In memory and especially in data transfer there will be errors and 
the stored or transferred data can become  corrupted. What  different 
means are used to certain  the correctness of data?
The decimal number 113, when moved to a peripheral device,  is changed 
to number 81 because of  transfer error disturbance. Show how the sender 
and the receiver should behave in order  that the receiver could  detect 
the received number as corrupted.  Is it possible  that the receiver could 
even  correct the  received number? (7 p) 

3. Explain in processor and register level detail how the CPU of the TTK-91, 
the example machine used in the course, acts when running the following 
series of instructions (10 p):

          ....
         ADD   R1, 200
         JUMP  100
         ....
      100  SVC  SP,=11       ;  service request HALT                
     
4. The life cycle  of a process can be described by  a state transition 
graph. Draw  the state transition graph of the process. Explain the meaning 
of the different states and state transitions, that is  when a process is 
in which state and what makes the process to move from one state to another. 
How are the data related to a process saved especially when the process is 
not running? (10 p)

5. Write, using  the TTK-91 assembly language, a function  Pow(X, n) that 
calculates the value of X^n  (X to the power n). Use stack to pass  the 
parameters and the return value. Write also a main program  that calls 
the subprogram Pow and  prints out the value returned  by the subprogram.  
The main program reads the values of X and n  from the keyboard  and checks 
that the exponent n is positive. 
Draw the content of the stack just after the subprogram call and before 
the subprogram has started to execute its first instruction. (10 p)

The results of the course will be ready by 15.9.1999. The course home 
page will give more information how the checking of the exam is progressing. 
The results, using shortened names of the participants,  will  also be shown 
in the course page.