WARNING: This site is intended for online use only; mass-downloading of pages degrades the server and is prohibited.
If you attempt to use tools to mass-download the site, you may be blocked permanently by automated software.
If you want to read this CertiGuide offline, please use one of the links on the left to purchase a convenient PDF copy. Thank you.

Like this CertiGuide? Get it in PDF format!
Click Here!

Custom Search






Table Of Contents  CertiGuide to A+ (A+ 4 Real)
 9  Chapter 7: History, Installing and Use of the MacOS
      9  You are Booted Up, Now What?

Previous Topic/Section
You are Booted Up, Now What?
Previous Page
Pages in Current Topic/Section
1
Next Page
Context Switching
Next Topic/Section

Multitasking and the Mac

To understand fully the concepts behind cooperative multitasking, pre-emptive multitasking and protected memory, we have to go back to comprehend the birth of multitasking. We will explore things that we all take now for granted and could not imagine spending a day without. First, we will look at the history and the cooperative multitasking used in Mac OS 9.

Way back when Macs were new, operating systems were made to be operated by one user working with one program. Obviously, this is no longer the case. Today, we want our computers to do more, faster, and with less work on our part. In order to understand these changes to task implementation, we have to explore a little more history.

Computer programs are a series of instructions stored in memory, and these instructions need data stored either in the microprocessor or in the RAM. These instructions are usually designed to carry out very specific tasks, like moving information from one location to another, compare the information and switch to subroutines depending upon the results of the comparisons. When these instructions are run by the microprocessor, it will keep track of where it is using a program instruction pointer.

At some level, such programs have total control over the computer at the time it’s running. At that time, the only code being executed is the code pointed to by the instruction pointer.

Those of us that can remember the 80s might remember programs that utilized a “main event loop”. This was code that ran hundreds of times a second, and the a command, specifically the “GetNextEvent” would interact with the rest of the OS, stopping the current program and passing control of the computer to the operating system. At this point, the OS saves the microprocessor state and the program counter. As soon as the OS is done, it reports to the program what activities were performed, and then the program can make any appropriate changes and move on.


Previous Topic/Section
You are Booted Up, Now What?
Previous Page
Pages in Current Topic/Section
1
Next Page
Context Switching
Next Topic/Section

If you find CertiGuide.com useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider buying an inexpensive PDF equivalent of the CertiGuide to A+ (A+ 4 Real) from StudyExam4Less.com. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

CertiGuide to A+ (A+ 4 Real) (http://www.CertiGuide.com/apfr/) on CertiGuide.com
Version 1.0 - Version Date: March 29, 2005

Adapted with permission from a work created by Tcat Houser et al.
CertiGuide.com Version Copyright 2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.