Understand the Interface that the OS Provides to the Software for Doing Input and Output | COMP 310, Assignments of Operating Systems

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COMP 310:

Operating Systems

Lecture 26:

Finish I/O

November 17, 2004

Christine Alvarado

Overview

 Understand the interface that the OS provides to the software for doing I/O

Review  What were the hardware components involved in I/O? Drivers  Definition: Software routines that provide a uniform device-access interface to the I/O subsystem.  Different HW controllers may have different interfaces. Drivers make them look the same.

Abstraction: Device categories  Goal: Group devices into similar I/O styles  Dimensions:  Block and Character  Network  Timers  Blocking and Non-blocking Block and Character  Block:  Character:

Network Devices  Network fundamentally different than local interaction Blocking and Non-blocking I/O  What is it?  Why is it not normally used? (exception: select() for network I/O)  What is used instead?

Buffering Caching  What is a cache?  Caching vs. Buffering

Spooling  Some devices need data complete and in order. Example? Error Handling  Kernel will retry I/O calls until they succeed.  Makes I/O failure invisible to user program

Part 1: Demand Paging  Proj 2: What happened when a new process started?  What we want:  Pages are allocated, but not filled  How will you do this? When will they be filled? Part 1 issues  page may straddle two segments (e.g. code and data)  While handling one page fault, ReadMem (or WriteMem) may generate another page fault  How could this happen?  What should you do?  You can no longer close the executable file when you exec a new process

Part 2: Backing Store/Page Replacement  Now, you no longer allocate pages up front  If memory is full, you have to write a page to disk  Need to keep track of whether pages are in memory or on disk  Only write a page if it has been modified  Issues  pages may come from files or from disk  Use any page replacement strategy Part 3: Testing  Start simple (using the same test programs from last time)  Then move to matmult, sort, and snake  Then write your own  Good locality  Bad locality  Random locality