CS439: Principles of Computer Systems

Discussion Section 8 Problem Set

Due in Section on Friday, March 28, 2025

The problem set must be completed before section and brought to section. To ensure that your problem set is turned in correctly and that you receive credit for discussion section, you must follow these guidelines exactly.

Include the following header at the top of your file:

Discussion Section Problem Set #:
Student Name:
EID:

You may either type your answers or write them by hand, but you must have a copy with you in discussion section.

In discussion section, your TA will check that you made a good effort on the problem set, you are participating in the discussions in section, and you are ready and able to answer when called upon. If all of those are true, you will receive credit for discussion section that day. Note that a "good effort" on the problem set includes that all answers are in words unique to you and not copied from anywhere else, including the slide deck.

The operating system gives memory to the heap memory manager k page(s) at a time. Why?
Assume a spinning disk. Where on that disk would you place the inode array? Justify your answer.
Determine the most appropriate form of stable storage for the following scenarios. Explain your reasoning.
1. The University needs to store files for legal purposes. These files are quite large and numerous, but are unlikely to be read.
2. Your parents want to store the data from their security cameras locally.
3. Your friend is building a new computer for general purpose use.
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. Your co-worker 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 hardware.

This won't quite work. In no more than two sentences, what did your co-worker forget?
Pooh Software Ltd. is selling a file system that uses a UNIX-like file system with multi-level indexing. For more reliability, the inode array is actually replicated on the disk in two different places. The intent is that if one or a group of sectors that are storing either replica of the array become bad, the system can always recover from the replica. Discuss the effect of having this replicated data structure on performance.
Susan would like to read the file
/usr/susan/cs439/study_guide.txt. Assuming she has the correct permissions and is using FFS, describe the steps the operating system would need to take to read the file.