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CompTIA A+ Certification All-in-One Exam Guide

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NOTE If you work with Windows long enough, you may encounter an

error message saying that Windows cannot boot because bootmgr is missing.

This message is generated when the boot sector code is unable to locate

bootmgr, which can be caused by file system corruption, a botched

installation, or viruses.

Once the operating system process takes over, it loads up all of the various

processes and systems that comprise Windows, the Windows logo comes up,

and you’re happily computing, completely oblivious to all of the complex

electronic communication that just took place inside your computer.

Applications, Processes, and Services

Back in Chapter 3, “CPUs,” you learned that CPUs run threads—bits of

programs that are fed into the CPU. Let’s see how all of this looks from

Windows’ point of view.

NOTE I’m simplifying things a little for the purposes of the CompTIA A+

220-1002 exam, but know that applications, processes, and services can get a

lot more complicated.

In Windows, programs are executable files waiting on a mass storage

device. When you start a program, Windows loads it into RAM as a process.

Once there, the CPU reads the process and the process tells the CPU which

chunks of code to run. Dealing with processes in their many forms is a big

part of understanding what’s happening “under the hood.”

Windows is a multitasking operating system, running lots of processes

simultaneously. Many of these processes appear in a window (or full screen)

when you open them and end when you close that window. These processes

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