Assignment 1

Comp 3730

Note: you are NOT allowed to re-copy text from the book, the Internet, other teams or other sources in your answers. You must use your own words and clearly express your answer, showing that you understand it. Otherwise, you will get a mark of 0 for that question.

You are allowed to work with one partner. No teams of three or more are allowed.

The assignment should be handed-in no later than January 19 at 12:30 in the assignment box of your lab instructor. No late assignments will be accepted. (12:35 is late!)

1.

a) Consider the idea of running another operating system on a virtual computer, that is, running an operating system as a program on another operating system.  There are two ways we could do this.  Discuss each one in terms of practicality and efficiency. [10]

·         Load the operating system code directly into the virtual computer (with no other additional software) and run it. This OS will only be able to use the instructions and system calls allowed by the underlying OS.

·         You first load an emulator into the virtual computer. The emulator creates a virtual version of some computer.  Then you load the operating system to run on this emulator.

b) What protection mechanisms are needed when implementing virtual machines? [5]

2.

a) What is the alternative to memory-mapped I/O? [5]

b) You have just been hired by Intel to work on the development of the new Pentium chip. The problem that you are asked to solve is as follows: To optimize performance, the processor currently allows cacheable memory reads to be reordered ahead of buffered writes. I.e. a memory write that comes before a memory read in a program is actually executed after. The problem is that with memory-mapped I/O, you may try reading the status of a device after a write, but you end up with the device status before the write is performed. Your job is to design two solutions that will force the processor to execute the program instructions in the order specified by the programmer. Describe your solutions. [10]

Hint: answers can be found on http://developer.intel.com/design/intarch/techinfo/Pentium/

 

3.

a) The interval timer only counts down to zero.  Suppose we wanted to keep the time of day.  How could we use the interval timer to keep the time of day? [5]

b) Some processors save the ia register and the psw register on a stack when an interrupt occurs.  What are the advantages and disadvantages of this? [5]

c) When executing an RTI instruction, first the contents of the iia register are moved to the ia register, and then the content of the ipsw register is moved to the psw register. Is the order of those instructions important? Why? [5]

d) Suppose a computer did not have a special system call instruction but it did have a typical interrupt system.  How could you simulate a system call instruction on such a computer? [8]

4.

a) Suppose we wanted to implement a linked data structure in a disk file rather than in memory.  Explain how you would use the read, write and lseek system calls to do this.  [8]

b) Write a program using the file system calls (open, creat, read, write, lseek, close, unlink) that determines the length of a file without using a loop in the code. [5]

c) Using the same file system calls, how can a programmer determine the current file position of an open file? [5]

5.

a) What are the advantages of named pipes (with names in the file system) over pipes with internal names?  Are there any disadvantages? [5]

b) In order for two processes to communicate by messages, they both have to know the qid of the message box that they will be using. This qid is normally passed to each process from their common parent. What could the OS designer do to allow two processes with no common parent communicate? i.e. how can they communicate the common qid? Describe three distinct solutions. [9]

6.

a) If you want to include an assembly language routine in a C++ program other than using an asm block, what do you need to do? [5]

b) Crowley describes the following system call:

int write( int openFileID, char * bufferAddress, int count);

Suppose that you make a write() system call and that no errors occur. Can write() return a value different than count? Explain. [5]

c) On page 69, the shell program is declared as follows:

void main (int argcount, char *arguments[ ])

What arguments might be passed to a shell? [5]