Lecture Notes for Operating Systems

Devices, 13 October 1999

1. objectives

   1. virtual machine - api

   2. performance - multiplexing, buffering, scheduling

2. block-oriented devices

   1. large chunks of data moved between system and device

   2. operations - open, close, read, write, ioctl, scatter-gather i-o

   3. partitioning

3. ram disks and other main store drivers

   1. ram disk - a section of main storage treated like a disk

   2. /dev/mem - access to physical main storage

   3. /dev/kmem - access to kernel space

   4. /dev/null - the null device

   5. implementation - straightforward

      1. open - where to create; what size; what name

      2. close - when to delete

      3. read, write - block or character oriented

      4. ioctl - set new sizes, gather statistics

      5. scatter-gather i-o - probably not relevent due to i-o speed

4. disks

   1. hardware - disks, cylinders, sectors

   2. controllers - handles much of the ugliness

   3. driver software

      1. disk arm scheduling

         1. arm movement expensive; reasonable response time; no starvation

         2. first come first served

         3. shortest next

         4. elevator algorithm

      2. caching - pre-fetch

      3. multiple devices off the driver

      4. error detection and correction - parameters; data errors, transient or permanent, hardware errors

This page last modified on 19 October 1999.