COMP-3300 Operating Systems Fundamentals
Winter 2020 — Course Project
This project consists of writing a program that translates logical to physical addresses for a
virtual address space of 216 = 65,536 bytes. Your program will read from a file containing logical
addresses and, using a TLB as well as a page table, will translate each logical address to its
corresponding physical address and output the value of the byte stored at the translated physical
address. The goal behind this project is to simulate the steps involved in translating logical to
physical addresses. Make sure your program uses fast operations like left/right shift operators.
Your program will read a file containing several 32-bit integer numbers that represent logical
addresses. However, you need only be concerned with 16-bit addresses, so you must mask the
rightmost 16 bits of each logical address. These 16 bits are divided into:
(1) an 8-bit page number, and
(2) an 8-bit page offset.
Hence, the addresses are structured as shown in the figure below:
Other specifics include the following:
• 27 = 128 entries in the page table
• Page size of 28 bytes
• 16 entries in the TLB
• Frame size of 28 bytes
• 128 frames
• Physical memory of 32,768 bytes (128 frames x 256-byte frame size)
• Virtual memory of 65,536 bytes = twice the size of physical memory
Additionally, your program needs only be concerned with reading logical addresses and
translating them to their corresponding physical addresses. You do not need to support writing
to the logical address space.
Your program will translate logical to physical addresses using a TLB and page table as outlined
in Section 8.5 of the textbook (the Paging section). First, the page number is extracted from the
logical address, and the TLB is consulted. In the case of a TLB-hit, the frame number is obtained
from the TLB. In the case of a TLB-miss, the page table must be consulted. In the latter case,
either the frame number is obtained from the page table or a page fault occurs. A visual
representation of the address-translation process appears in the figure below:
Handling Page Faults
Your program will implement demand paging as described in Section 9.2 of the textbook (the
Demand Paging section). The backing store is represented by the file BACKING_STORE.bin,
a binary file of size 65,536 bytes. When a page fault occurs, you will read in a 256-byte page
from the file BACKING_STORE and store it in an available page frame in physical memory. For
example, if a logical address with page number 15 resulted in a page fault, your program would
read in page 15 from BACKING_STORE (remember that pages begin at 0 and are 256 bytes in
size) and store it in a page frame in physical memory. Once this frame is stored (and the page
table and TLB are updated), subsequent accesses to page 15 will be resolved by either the TLB
or the page table.
You will need to treat BACKING_STORE.bin as a random-access file so that you can randomly
seek to certain positions of the file for reading. We suggest using the standard C library functions
for performing I/O, including fopen(), fread(), fseek(), and fclose().
Specific for the Three-Students-Project: The size of the physical memory is smaller than the
size of the virtual address space —65,536 bytes— so you need to be concerned about page
replacements during a page fault. Since there are only 128 page frames rather than 256, you are
therefore required to keep track of free page frames as well as implementing a page-replacement
policy using either FIFO or LRU; see Section 9.4 of the textbook (the Page Replacement
We provide the file addresses.txt, which contains integer values representing logical addresses
ranging from 0 to 65535 (the size of the virtual address space). Your program will open this file,
read each logical address and translate it to its corresponding physical address, and output the
value of the signed byte at the physical address.
How to Begin
First, write a simple program that extracts the page number and offset (based on the first figure
above) from the following integer numbers:
1, 256, 32768, 32769, 128, 65534, 33153
Perhaps the easiest way to do this is by using the operators for bit-masking and bit-shifting.
Once you can correctly establish the page number and offset from an integer number, you are
ready to begin.
Initially, we suggest that you bypass the TLB and use only a page table. You can integrate the
TLB once your page table is working properly. Remember, address translation can work without
a TLB; the TLB just makes it faster. When you are ready to implement the TLB, recall that it
has only 16 entries, so you will need to use a replacement strategy when you update a full TLB.
You may use either a FIFO or an LRU policy for updating your TLB.
Alternatively, you may (1) first complete the project Project-For_One_Student, then modify it
to complete the project Project-For_Two_Students, and then modify it to complete your course
How to Run Your Program
Your program should run as follows:
Your program will read in the file addresses.txt, which contains 1,000 logical addresses ranging
from 0 to 65535. Your program is to translate each logical address to a physical address and
determine the contents of the signed byte stored at the correct physical address. (Recall that in
C, the char data type occupies a bye of storage, so we suggest using char values.)
Your program should output the following values:
1. The logical address being translated (the integer value being read from addresses.txt).
2. The corresponding physical address (what your program translates the logical address
3. The signed byte value stored at the translated physical address.
We also provide the file correct.txt, which contains the correct output values for the file
addresses.txt. You should use this file to determine if your program is correctly translating
logical to physical addresses.
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