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Lecture Notes on Computer Systems | CMSC 412, Study notes of Operating Systems

University of Maryland Operating Systems

Prof. Jeffrey K. Hollingsworth

Material Type: Notes; Professor: Hollingsworth; Class: Operating Systems; Subject: Computer Science; University: University of Maryland; Term: Unknown 1989;

Typology: Study notes

Pre 2010

Uploaded on 02/13/2009

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CMSC 412 - S96 (lect 02))

Announcements

●Programming assignment #1 was handed out

●Reading for next week:

– Chapter 3 (sections 3.2 to 3.9)

●Classroom

– class will meet in Chemisty 115

●Programming Assignment #0

– object file available on the web page

Discover Study notes of Operating Systems University of Maryland

Partial preview of the text

Download Lecture Notes on Computer Systems | CMSC 412 and more Study notes Operating Systems in PDF only on Docsity!

Announcements

Programming assignment #1 was handed out

Reading for next week:– Chapter 3 (sections 3.2 to 3.9)

Classroom– class will meet in Chemisty 115

Programming Assignment #0– object file available on the web page

Why Study Operating Systems?

They are large and complex programs– good software engineering examples

There is no perfect OS– too many types of users

real-time, desktop, server, etc...
- many different models and abstractions are possible
  - OS researchers have been termed abstraction merchants

Many levels of abstraction– hardware details: where the bits really go and when– high level concepts: deadlock, synchronization

Computer Systems

Computers have many different devices– I/O Devices– Memory

volatile storage
- Processor(s)

Processor

Memory Mem. Controller

I/O Bus Controller

Memory Bus

I/O Bus

Display Adapter

SCSI Adapter

SCSI Bus

Disk Drives

Tape Drive

Optical Drive

Network Adapter

Network

I/O Systems

Many different types of devices– disks– networks– displays– mouse– keyboard– tapes

Each have a different expectation for performance– bandwidth

rate at which data can be moved
- latency
  - time from request to first data back

Issues In Busses

Performance– increase the data bus width– have separate address and data busses– block transfers

move multiple words in a single request

Who controls the bus?– one or more bus masters

a bus master is a device that can initiate a bus request
- need to arbitrate who is the bus master
  - assign priority to different devices• use a protocol to select the highest priority item
    - daisy chained– central control

Disks

Several types:– Hard Disks - rigid surface with magnetic coating– Floppy disks - flexible surface with magnetic coating– Optical (read only, write once, multi-write)

Hard Disk Drives:– collection of platters– platters contain concentric rings called tracks– tracks are divided into fixed sized units called sectors– a cylinder is a collection of all tracks equal distant from the

center of disk

Current Performance:
- capacity: megabytes to tens of gigabytes• throughput: sustained < 10 megabytes/sec• latency: mili-seconds

I/O Interrupts

Interrupt defined– indication of an event– can be caused by hardware devices

indicates data present or hardware free
- can be caused by software
  - system call (or trap)
    - CPU stops what it is doing and executes a handler function
      - saves state about what was happening• returns where it left off when the interrupt is done

Need to know what device interrupted– could ask each device (slow!)– instead use an interrupt vector

array of pointers to functions to handle a specific interrupt

I/O Operations

Synchronous I/O– program traps into the OS– request is made to the device– processor waits for the device– request is completed– processor returns to application process

Asynchronous I/O– request is made to the device– processor records request– processor continues program

could be a different one
- request is completed and device interrupts– processor records that request is done– program execution continues

Lecture Notes on Computer Systems | CMSC 412, Study notes of Operating Systems

Related documents

Partial preview of the text

Download Lecture Notes on Computer Systems | CMSC 412 and more Study notes Operating Systems in PDF only on Docsity!

Announcements

Programming assignment #1 was handed out

Reading for next week:– Chapter 3 (sections 3.2 to 3.9)

Classroom– class will meet in Chemisty 115

Programming Assignment #0– object file available on the web page

Why Study Operating Systems?

They are large and complex programs– good software engineering examples

There is no perfect OS– too many types of users

Many levels of abstraction– hardware details: where the bits really go and when– high level concepts: deadlock, synchronization

Computer Systems

Computers have many different devices– I/O Devices– Memory

I/O Systems

Many different types of devices– disks– networks– displays– mouse– keyboard– tapes

Each have a different expectation for performance– bandwidth

Issues In Busses

Performance– increase the data bus width– have separate address and data busses– block transfers

Who controls the bus?– one or more bus masters

Disks

Several types:– Hard Disks - rigid surface with magnetic coating– Floppy disks - flexible surface with magnetic coating– Optical (read only, write once, multi-write)

Hard Disk Drives:– collection of platters– platters contain concentric rings called tracks– tracks are divided into fixed sized units called sectors– a cylinder is a collection of all tracks equal distant from the

I/O Interrupts

Interrupt defined– indication of an event– can be caused by hardware devices

Need to know what device interrupted– could ask each device (slow!)– instead use an interrupt vector

I/O Operations

Synchronous I/O– program traps into the OS– request is made to the device– processor waits for the device– request is completed– processor returns to application process

Asynchronous I/O– request is made to the device– processor records request– processor continues program