Today : Tue, 21 May 13 .

# CS537 - Section 2 - Fall 2011

## Homework4-fa11

This homework is optional. If you do it and hand it in, it will count towards your final grade.

### Question 1: Memory Protection

The entries in a page table contain page frame numbers for virtual page numbers.

• a. What is the effect of allowing two entries in a page table to contain the same page frame number?
• b. How could this effect be used to decrease the amount of time needed to copy a large amount of memory from one place to another?
• c. What effect does updating some byte on one page have on the other page?

### Question 2: Page table organization

A virtual address comprises a virtual page number and an offset within the page.

• a. For a 32 bit virtual address with a 4kb page (12 bits), and 32 bit physical addresses, what is the minimum size of a page table entry?
• b. How much space does a page table mapping the complete 32-bit address space take up? Hint: one entry is needed for each page.
• c. Suppose that you increase the page size to 64 KB (2^16 bytes). What is the minimum size of a page table entry now? How much space is required for the entire page table mapping all addresses?

Consider a logical address space of 128 pages of 1024 bytes each, mapped onto physical memory of 32 frames

• a. How many bits are there in the logical (virtual) adddresses?
• b. How many bits are there in the physical addresses?
• c. Draw a picture showing how, with a single page table, logical addresses are converted into physical addresses