CS439: Principles of Computer Systems
Homework 7, Part 1
Due: 8:45a Friday, March 21, 2014 Part 1 of the
homeworks must be submitted electronically. Please refer to the
homework turnin instructions.
Name two advantages of paging over relocation.
Consider a multi-level paging system with 128 pages and a page size
of 256 bytes. The system has 1024 bytes of physical memory and is
byte addressable. Assume the first-level page table holds 8
- How many bits are in a physical address?
- How many bits of the virtual address represent the
first-level page table?
- How many bits of the virtual address represent the page number?
- How many bits are in the complete virtual address?
- What size are the page frames?
Question 9.19, page 852, B&O.
The Operating System gives memory to the heap memory manager k
page(s) at a time. Why?
In some operating systems, I/O from/to disk is done directly to/from a
buffer in the user program's memory. The user program does a system
call specifying the address and length of the buffer (the length must
be a multiple of the disk record size).
The disk controller needs a physical memory address, not a virtual
address. Ben Bitdiddle proposes that when the user does a write
system call, the operating system should check that the user's virtual
address is valid, translate it into a physical address, and pass that
address and the length (also checked for validity) to the disk
This won't quite work. In no more than two sentences,
what did Ben forget?