Computer Science 432 Operating Systems Williams College Fall 2006

Agenda

• Announcements
• Lecture assignment recap
• Working Sets (see outline from last lecture)
• Segmentation
  • like paging, but with variable-sized segments instead of fixed-size frames
  • allocate segments according to logical breakdown of memory usage
  • segment table requires base and offset
  • external fragmentation can be a problem (as with the contiguous allocation approach)
• Combinations of Segmentation and Paging
  • Intel Pentium memory hardware
    • Lots of details in IA-32 Intel Architecture Software Developer's Manual, Volume 3: System Programming Guide, available in shared area. Don't print it - it's over 800 pages. Memory management is described in great detail in Chapter 3.
    • Better: excerpt from newest Tanenbaum OS text (see handout).
  • FreeBSD approach
• Files and File Systems
  • Disks and disk structures
    • disk is arranged into cylinders, divided into sectors, which contain blocks
    • this arrangement is the drive geometry
    • hard to determine the real values in modern disks
  • access: line up read/write head over desired block
  • access time
    • seek time - time to move the read/write head
    • rotational latency - time to get the correct block under the read/write head

Lecture Assignment

Due at the start of class, Thursday, November 9.

Turn in short answers to these questions. Please turn in a hard copy (typeset or handwritten are OK). We will discuss these questions during class, so no late submissions are accepted.

SG&G 9.10, 9.14, 9.15

The readings for next time are SG&G Chapter 10.