Module 3 (Lectures 11-15) Introduction to Operating Systems and Virtual Memory
1. Find out how to get a system call trace (details of the sequence of system calls
made by a program when executed) in a Linux system. Use this facility to find out
what system calls are used: (i) by the dynamic memory allocation library, (ii)
during file I/O, (iii) during terminal I/O, (iv) as part of program startup, (v) as part
of program termination.
2. A `shell’ is a program that does command interpretation. It takes commands typed
in by a user and causes them to be executed. The `command’ could be the name
of an existing executable program or one of several `shell commands’ provided by
the shell program. You might have used a shell (such as csh, tcsh or bash) before.
Write a shell program that can do the following: It should prompt the user for
input. The user could respond with the full file name of an executable program
file he/she wishes to execute, where the file name would be terminated by the
ampersand character (`&’) to indicate immediate re-prompt (a feature that is
supported by many shells). In addition, your shell program should be capable of
responding to the following shell commands that the user can also type in (the
meaning of each is given as a comment):
prompt ‘string’ / change the shell prompt to the string provided
exit / terminate shell
!! / re-execute the previous command
time / print current time
3. A given computer system has paged virtual memory, with page size of 4 KBytes.
A 24 bit virtual address gets translated into a 32 bit physical address. Given below
is information from the current state of some valid pages in the page table
corresponding to a given process (values in the table are in decimal).
Virtual Page
Number Physical Page
Number
11 1023
12 47
13 2047
14 255
Consider the following 5 virtual addresses: 0x1A093, 0xD100, 0xF0D1, 0xA093
and 0xE0D0. (i) Which of these virtual addresses are on the same virtual page?
(ii) Show the physical addresses (in hexadecimal) for all of the virtual addresses
above that can be translated using the available information.
4. During its execution on a system with paged virtual memory, a particular program
references its virtual pages in the following sequence (virtual page numbers are
given in hexadecimal): A, B, C, D, E, F, A, A, D, C, E, D, A, B, F, C. Assuming
that the main memory is of size 4 physical pages and was initially empty, which
of these page references will result in page faults if the operating system uses (a)
FIFO replacement, (b) LRU replacement
5. The Linux time command can be used to determine how many page faults
occurred when a program was executed. Read the manual entry for this command
to learn how to use it for this purpose. Use time to discover the paging properties
of programs that you frequently use.
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