computer basics

Time This lesson takes approximately 30 minutes to complete.

Goals Describe a computer’s basic hardware components

Distinguish normal from abnormal computer operation

5a

1

This lesson covers the most basic physical components of a computer

system and the basic elements of the operating system. It also provides an

introduction to what happens when a computer starts up, so that you

can troubleshoot a computer that isn’t starting up properly. Though

you may already be familiar with this material, even if you only use it

as a refresher, this lesson will help you discuss Macintosh support

questions with your customers.

Before you can isolate or resolve trouble in an Apple product, you must

be able to distinguish normal from abnormal operation. By familiarizing

yourself with normal operation, you will be better able to recognize the

problems your customers try to describe.

If you think you already know this material, start with the Lesson

Review. If you complete the review without error or consulting the

text, you can skip to the next lesson.

Lesson 5a

Basic Computer Theory and Terms

Basic Hardware ComponentsWe’re going to take a look at the internal components of a Macintosh computer,

and understand how they work individually and together.

At the simplest level, a computer system consists of:

� input devices such as keyboards and mice

� output devices such as monitors and speakers

� a “box” containing the computer’s processor(s), also known as central

processing unit (CPU), memory (RAM), disk drives, external ports,

and video circuitry

Within each of these components are numerous subcomponents that must

work together to enable the computer system to work correctly.

While this isn’t a detailed comprehensive look at the inside of the computer, we

will cover all of the major pieces. The components discussed in this lesson are:

� Processor: The brain of the computer is located on the main logic board

(MLB). This is where the operating system (OS) works, games render

images, and spreadsheets calculate. Most Apple computers use one of

four types of processors: PowerPC G4, PowerPC G5, Intel Xeon, or Intel

Core Duo.

� RAM: This is where the processor keeps information on which it works.

� Cache: This is a section of RAM that is assigned a specific function.

� Drives: These store all of the information you process and make on a

Macintosh. There are two basic types of disk drives, magnetic and optical;

we’ll take a look at both.

� USB: One of the interconnect technologies used on the Macintosh to con-

nect peripherals, Universal Serial Bus (USB) is intended for slower, less

demanding peripherals, such as keyboards and mice, although it can be

used to connect disk drives and cameras.

2 Basic Computer Theory and Terms

� FireWire: This high-speed counterpart to USB is also known as IEEE 1394

and iLink.

� Expansion slots: No one’s ever satisfied with their computer, right? Always

wanting to add things, like a graphics card for another display. You can

add cards in these slots to support additional functionality. We’ll examine

both types of slots used today: Peripheral Component Interconnect (PCI)

and Accelerated Graphics Port (AGP).

Once we have all the pieces down, we’ll then look at how they work together to

make your computer do what you want it to (well, most of the time anyway)

in the startup process.

Processors

Processors are silicon wafers made up of tens of thousands of tiny transistors.

These transistors have two states: on and off. This is reflected in the use of

binary code to communicate inside the processor and with other components

of the computer. A clock providing timing signals (called cycles) synchronizes

the processor signals. The speed of the clock is measured in megahertz (MHz)

or gigahertz (GHz), which means millions or billions of cycles per second.

A lot happens in a processor during one clock cycle. A processor works with

instructions, which are commands from the software. It may take several

instructions to complete a task. The G4 processors, for example, can issue up

to 20 instructions per cycle thanks to parallel processing, or working on more

than one instruction at a time.

Basic Hardware Components 3

We should pause here and note the difference between an instruction and data.

An instruction is a command issued by the processor. This instruction is made

up of, and will produce, data. A processor’s performance is measured by both

the number of instructions it can process and the amount of data it can move.

To gain even more efficiency, today’s processors are usually composed of mul-

tiple execution units that operate independently and simultaneously, but on

different instruction types. Execution units are built onto a specific physical

area of the processor chip, have specific strengths, and work only on a certain

type of instruction. Depending on the nature of the instruction, it will be

routed to and processed by the appropriate execution unit.

One of the execution units is called the integer unit. Integer math is the most

common type of calculation used by software. Another execution unit is the

floating-point unit. Floating-point calculations are common in graphical and

mathematical software.

PowerPC G4 Processor

The PowerPC G4 processor introduced a new execution unit called the vector-

processing unit. Apple called this unit the Velocity Engine; Motorola referred

to it as AltiVec. This unit could process 128 bits of data in one cycle instead of

the standard 32 or 64 bits common in other processors. This enabled the unit

to perform demanding tasks such as speech recognition and compression or

real-time encoding of video or sound. The only catch was that software had to

be rewritten to take advantage of the Velocity Engine.


As complicated and advanced as the processor was, its efficiency depended

heavily upon the instructions fed to it by software. The operating system and

applications must be well written to take maximum advantage of processors.

PowerPC G5 Processor

The Power Mac G5 marked the arrival of 64-bit computing to the personal

computer market. The development of the PowerPC G5 built on previous

PowerPC designs, combining an optimized Velocity Engine that supports up

to 215 simultaneous in-flight instructions.

Intel Xeon and Core Duo Processors

All new Macintosh computers now use either Intel Xeon or Intel Core Duo

processors, which have brought significant increases in performance while

reducing heat output. In subsequent lessons, we will examine the service and

troubleshooting consequences of this latest transition.


RAM

The memory used by processors in computers today is known as dynamic

random-access memory (DRAM, or just RAM). Random access means that

any of the data contained in this memory can be accessed directly, very similar

to the way you would access a particular song on a CD. Accessing a song on a

cassette tape would be an example of linear access, because you have to wind

through the tape to get to a particular song.

The contents of RAM are present only as long as the computer is powered.

Shut down the computer and all of the RAM content is lost.

There are different configurations of RAM, and this can be confusing, especially

when deciding what RAM goes in your Macintosh. In addition, some Macintosh

computers need RAM installed in DIMM pairs. RAM changes every time the

processor changes and sometimes more often. This change is necessary so that

RAM can keep up with the continually advancing processors. If the RAM did

not change, you would likely not see as much of a performance increase from

processor to processor.

Here are the different types of RAM that will work with Macintosh computers:

� DIMM (dual inline memory module): larger capacity and faster than

SIMMs (single inline memory module)


� SO-DIMM (small outline dual inline memory module): more expensive

due to smaller packaging (about half the size of a DIMM)

� SDRAM (synchronous dynamic RAM): internal clock synchronized with

processor clock for better performance

� FB-DIMM (fully-buffered dual inline memory module): this is a memory

design from Intel that uses serial communication between the FB-DIMM

and the memory controller. Unlike other designs, it uses different paths

for transmission and reception of data.

The Apple Specifications website (www.apple.com/support/specs) contains

information on the RAM type used by a specific Macintosh system.

MORE INFO � The following Apple Knowledge Base documents list

which RAM is compatible with which computers: 20434, “Power

Macintosh: Memory Configurations”; 58007, “iMac (All Models):

Memory Specifications and Upgrades”; 14870, “Memory Configurations:

Portable, PowerBook, iBook”; and 86414, “Power Mac G5 Memory

Specifications and Requirements.”

Video Memory

Video cards in newer Apple computers—iMac (Flat Panel), PowerBook G4,

Power Mac G4—incorporate DDR RAM (double data rate RAM). Here are

some additional RAM-related definitions:

� VRAM (video RAM): Same as DIMMs, but dedicated to video output and

processing.

� SGRAM (synchronous graphics RAM): Synchronizes with the graphics

processor for better performance. Same as SDRAM.

� DDR-SDRAM (double data rate synchronous DRAM): Doubles the memory

chip’s data throughput. Consumes less power. Also called SDRAM II.


Cache

Cache is closely related to RAM and it greatly affects processor performance.

In computer terms, cache is RAM or hard drive space used to store frequently

used bits of code or data. Today cache exists in many different places in a com-

puter system. Some hard drives have it. CD recording drives have it. Processors

have it at one or more levels. Cache is used primarily to speed up the system.

Let’s look at processors for a moment. Processors are incredibly fast—much

faster than anything else on the logic board, including RAM. Quite often, the

processor is waiting on information from another source to complete its tasks.

To minimize the wait time associated with accessing data from main memory,

most processors have a small amount of RAM built into the processor that is

used to store bits of frequently used code, increasing processor efficiency and

throughput. This RAM is called Level 1 (L1) cache and ranges in size from

32 KB to 256 KB on modern processors. With applications and operating

systems becoming more complex, a larger cache would be helpful. However,

processors are getting smaller and more energy conscious, so there isn’t much

room for a larger Level 1 cache. Enter the Level 2 (L2) cache.

L2 cache is not on the processor, but is located very close to it and has a higher

speed connection than is available to other components. Level 2 cache is often

larger than Level 1 cache, ranging from 256 KB to 1 MB or larger. In addition

to the 256 KB L2 cache, some PowerPC G4 microprocessor configurations also

had Level 3 (L3) cache. The Power Mac G5 processor further enhanced the L1

and L2 caches.

Another cache used frequently in computers is called disk cache. This works

the same way as other caches, but sets aside a bit of RAM to store frequently

used data from the hard drive. Accessing RAM is much faster than accessing

the hard drive, so performance is increased. You can see this for yourself. Next


time you start up a Mac, open the hard disk icon on the Finder desktop. The

first time you do this, you’ll hear the hard drive being accessed. Once the win-

dow opens, close it and open it again. The window will open instantly and the

hard drive is not accessed. This is the disk cache in operation.

Drives

Your Macintosh needs some place to store the operating system, applications,

and the files you create when they are not in use or the power is off. RAM

loses power along with the rest of the computer, so you can’t leave information

in there. You need something more permanent.

Disk drives are the answer. These are drives that contain platters that spin.

Information is written to the platter in a series of 1s and 0s. Since the information

is written to the drive in a “permanent” fashion, the data is retained even

though the computer is shut down. Permanent is a relative term, and here

means compared to the rest of the computer. It is still possible to lose data on

a disk drive through negligence, accident, abuse, or environmental situations.

There are two basic types of disk drives: magnetic and optical. Which one you

use depends on several different factors. Let’s look at both types and some

examples of each. We’ll also discuss the pros and cons and describe the best

use of each type.

Magnetic Drives

Hard drives, floppy drives, and Zip drives all have at least one thing in common:

They all store data on disks using magnetism. In this section we’ll focus on the

hard drive, but the principles are basically the same for all magnetic drives.


Hard drives contain one or more disks or platters that spin around at several

thousand revolutions per minute. Typical speeds for hard drives range from

5,400 to 10,000 rpm. Usually the faster the platter spins, the faster data can be

retrieved off of the drive. These platters are made of a material that can be

magnetized.

Positioned closely over the surface of the platter is an electromagnetic coil

known as the drive head. By switching the electrical current to this head, the

head can affect the particles on the platter. The particles in the area of the plat-

ter affected will be magnetized and have a north and south pole. An area with

a north pole in one direction will be a 1 and an area oriented in the opposite

direction will be a 0. Reversing the current of the head changes how the parti-

cles on the platter are affected.

Reading the particles happens in the reverse. As the heads pass over the parti-

cles, a current is generated in the coil. A current in one direction is a 1, the

other a 0.

Most hard drives also contain a cache. This cache is used to store frequently

requested data. When a call comes for data from the hard drive, the cache is

checked first. Considerable time can be saved if the data can be sent from

there instead of accessing the platters.

Most hard drives today contain multiple platters and multiple heads. The

heads are all connected and move at the same time. The platters are also all

connected and spin at the same speeds.

Formatting a disk prepares it to contain data. There are two types of format-

ting on any disk: physical and logical.

Physical formatting refers to what is actually done to the surface of the disk.

Concentric rings, called tracks, are created by strongly magnetizing particles to

create boundaries. These tracks are very similar to the tracks on a vinyl record.

The tracks are then divided into sectors.

Logical formatting refers to keeping track of the data within the physical for-

matted boundaries. Blocks of data are created using sectors. Blocks are not

physical, but instead are notations of which sectors contain the data. Blocks


are the smallest amount of data that is moved on or off a platter. Blocks may

cover several sectors and will never contain partial sectors.

Partitions are created using software, but are physically determined on the

platter. Strongly magnetized boundaries are created marking the beginning

or end of a partition. Partitioning a large drive into smaller drives can

increase system performance since it cuts down on the area to search when

retrieving data.

Optical Drives

Optical drives use light to read and write information to and from discs. While

the principle of operation is similar to magnetic drives, there are some crucial

differences.

CDs and DVDs are made up of a recording layer, usually aluminum, sand-

wiched between a protective plastic covering. When data is recorded onto the

discs, it is done in a series of pits and lands. Pits absorb the light from the

laser while lands reflect it. So pits are 0s and lands are 1s.

Another difference from magnetic drives is the way the data is laid onto the

discs. Instead of tracks, the data is recorded onto the disc in a single spiral

track beginning at the center of the disk. Because of this, CDs will spin at a

variable rate depending on the location of the laser. The CD will slow down as


the head moves toward the outer edge. By doing this, the head maintains the

same velocity over the data.

CD-RW, DVD-R, and DVD-RAM drives have yet another subtle difference.

Media used in these drives are made of crystalline material that loses its struc-

ture when heated by the laser of the drive. When the structure is lost, that area

of the drive loses its reflectivity. So instead of pits and lands on this media, you

have bright spots and dark spots. CDs have a capacity of 650–700 MB; DVDs

have a capacity of 4.7–17 GB.

MORE INFO � For more information on DVD technology, refer to Knowledge

Base document 24451, “DVD Technology: Overview.”

USB

You can attach peripherals to your Macintosh through either of two buses,

USB and FireWire. USB is generally used for slower devices like keyboards

and mice; FireWire is used for high-speed devices such as hard drives and

digital camcorders. Both of these are built in to all Macintosh computers

shipping today.

USB is capable of supporting 127 devices on one bus. Most of the Macintosh

computers today have two USB buses, giving you the option of a total of

254 devices connected to one computer.


To connect that many devices, you need USB hubs. Hubs give you multiple

USB ports. Some devices, such as the USB keyboard that comes with iMac and

Power Mac G4 models, have built in hubs, which enable you to connect another

USB device to the available port on the keyboard.

USB can supply a small amount of power to devices. The mouse, for instance,

is powered by USB. As long as the device does not need more than 500 mA at

5 volts, it can draw power from USB. Any peripheral that requires greater than

500 mA at 5 V, such as a printer or scanner, would need external power to be

supplied.

USB is a hot-pluggable bus, meaning the computer does not need to shut

down or restart to connect peripherals. The Macintosh will recognize that a

device has been connected right away and will look for drivers to communi-

cate with it.

USB transfers data at either 1.5 megabits per second (Mbit/s) or 12 Mbit/s. It

can transfer both speeds at the same time, as in the case when you have a key-

board (which uses the 1.5 Mbit/s speed) and a camera (using 12 Mbit/s) con-

nected. USB 2.0 devices can transfer data at a rate of 480 Mbit/s.

We have the USB specifications, but how does USB work? The Mac OS keeps

track of USB devices in the USB Manager. This software identifies and assigns

addresses to and monitors priority of USB devices. Priority determines the

type of data flow to and from the device. Isochronous transfer is the highest

priority, permitting a continuous stream of data without interruption. A digi-

tal speaker is one such device that would require isochronous transfer.

Devices are connected using a two-pair (four-wire) cord. One pair is used for

data and control signals and the other pair is used for power. The two wires in

the data pair are called Data+ and Data–. When a device is connected to USB,

it causes a change in voltage in one of these two wires. A signal on Data+ indi-

cates the device is high speed, while a signal on Data– indicates a low-speed

device.


Finally, drivers allow the OS and applications to communicate with the USB

device. Some drivers are known as Class drivers. These drivers work with a

variety of devices. Apple includes two Class drivers, one for keyboards and

mice, the other for hard drives. Other devices, such as printers, may require

specific drivers.

You’ll learn more about USB and USB 2.0 in Lesson 5b, “Underlying Tech-

nologies,” on this book’s companion website, www.peachpit.com/ats.deskport3.

FireWire

So what if you need more speed than USB provides? Transferring large quanti-

ties of data at 12 Mbit/s can take a while. Enter FireWire.

FireWire is a serial bus just like USB. You can connect up to 63 devices on one

port or bus. Yet FireWire has a more complex communication protocol than

USB. FireWire cable uses a three-pair cord. Two pairs of wires transferring

data and faster signaling helps FireWire achieve faster transfer rates than USB.

You’ll learn more about FireWire and FireWire 800 in Lesson 5b.

Expansion SlotsSome desktop Macintosh computers have expansion slots built in. These slots

let you add more memory, a second hard drive, or an AirPort Extreme Card

quickly and easily.

There are two basic types of busses that provide communication between slots

and the logic board: PCI and AGP.


PCI

Peripheral Component Interconnect (PCI) is one of the main busses of the

computer. It handles communication between the processor, all expansion

slots, and the USB, Bluetooth, and AirPort ports through intermediary bus

bridge electronics. These electronics on the logic board and software in the

Mac OS help facilitate the flow of data between all of the components.

When a Macintosh starts up, software called Open Firmware in the PCI card’s

ROM contacts software in the Name Registry on the Macintosh. The configu-

ration and location of the card are stored in the Macintosh RAM. Open

Firmware then checks to see if it’s in a Macintosh or PC.

Some cards, however, don’t need to be loaded at startup. A network card, for

example, doesn’t load until its driver, an extension located in the Mac OS,

loads as the operating system loads.

There are several different versions of PCI. Understanding their differences will

enable you to resolve compatibility issues when installing peripheral cards:

� The original PCI standard allows for up to 66 MHz clock speed and a

maximum transfer rate of 133 MB/s.

� PCI-X allows for up to 133 MHz clock speed and a maximum transfer rate

of 533 MB/s.

� PCI Express has a maximum transfer rate of 4000 MB/s.

You’ll learn more about PCI technologies in Lesson 5b.

AGP

Some Macintosh computers have an Accelerated Graphics Port (AGP) slot,

which is actually just an enhanced PCI slot. It’s built on the same protocol, but

under certain circumstances can transfer data at a faster rate. The AGP slot

also has a faster bus to the Macintosh computer’s main RAM.


Users are demanding more and more performance out of their computers, and

one area under the most demand is graphics. Whether it’s the latest games, 3D

rendering, or video editing, faster graphics are required.

The AGP slot does not multiplex addresses and data, but keeps them separate.

Because of this, the AGP bus can process multiple addresses at the same time,

improving performance.

The UniNorth chip acts as the AGP controller chip. One of its functions is to

remap data in the Macintosh computer’s main RAM to make it more readily

accessible to the AGP bus. This speeds up access to large chunks of data, the

kind of data you would see with video or 3D images.

Now that you have a good grasp of the components that make up a Macintosh

and a how they communicate, it’s time to take a look at the software that tells

the components what to do.

Basic Software ComponentsA computer needs instructions in order to run. It gets these instructions in the

form of firmware and software.

FirmwareFirmware is a combination of software and hardware: a computer chip that

has data and/or software instructions recorded on it. These chips commonly

include the following:

� ROM (read-only memory)

� PROM (programmable read-only memory)

� EPROM (erasable programmable read-only memory)

Many Apple products contain firmware for various functions, including help-

ing the computer start up and remembering various system settings when

the computer is shut down. Firmware is designed to be updated, if necessary,

through a downloadable firmware update.


MORE INFO � To learn more, read the following Knowledge Base docu-

ments: 93772, “What is Firmware?”; 58492, “Differences Between the

Mac OS ROM and bootROM”; 86117, “Mac OS X: Available firmware

updates”; 303364, “About firmware updates for Intel-based Macs”; 303880,

“Mac OS X: Firmware Updates for Intel-based Macs”; and 303725, “About

the SMC Firmware Updates.”

Software Software is data (information), made up of instructions used to accomplish a

task. We associate software most often as being stored on media, such as a disk

(hard disk, CD-ROM, DVD). However, software can be stored on any record-

able medium.

We most often associate software as being used by computers. But software is

used in many situations where complex tasks need to be carried out—for

example, handling emissions controls in an automobile.

Software can be divided into two primary categories: system software and

application software.

System software manages computer hardware. It also provides a graphical user

interface (GUI) to display items on the screen. System software includes the

operating system (Mac OS), software drivers (for example, to display video or

Basic Software Components 17

read a CD-ROM), and software needed to interact with the user (for example,

the software that understands function key assignments). The terms system

software and operating system are interchangeable for most users.

Apple releases system software online or through retail outlets for existing Apple

hardware. Apple also releases system software bundled (included) with new

computers.

Application software is a program that processes data for a user. An application

can be any number of things, like a word processor or multimedia program.

Application software generally relies on the operating system for compatibility

with hardware.

Like system software, application software is released individually or bundled

with computers. For example, iDVD is bundled with computers; DVD Studio

Pro is released individually.

The process of continually improving software results in new versions of the

software becoming available. When this happens, Apple releases these changes

through a reference release, software upgrade, or software update.

The term “reference release” means that the software is distributed as a stand-

alone system software package that can be installed regardless of the version of

Mac OS currently installed. When Apple uses the term “software upgrade,” it

means a major, standalone version of a software product. Such products are

usually purchased in a box or shrink-wrapped package.

An update is generally smaller than an upgrade It is usually something you

can download, unlike a major software upgrade. It’s wise to install the latest

updates available for a software product. You can use an update only if there is

a prior version of the software installed on your computer. Mac OS upgrades

are sometimes also called maintenance releases.

Version numbers are used to describe changes in software—sort of like age is

to a person. The version number can be defined as “reference.upgrade.update,”

though this numbering is often not followed. The idea is that there are fewer

changes between a 10.4.1 and 10.4.2 release as there would be between a 10.3

and 10.4 release.


MORE INFO � Consider reading these three Knowledge Base documents

about the different kinds of software release: 58070, “Mac OS: What is

a Reference Release?”; 25784, “What’s a ‘computer-specific Mac OS X

release’?”; and 25811, “Software update, upgrade—what’s the difference?’

Let’s review some of the other terms we’ll be using in this book:

� File: an item that contains information

� Application: a file that performs a task or program

� Document: a file that is created by an application

� File system: the mechanism used by the operating system to retrieve and

store files

� Icon: a graphical representation of a file

Computer OperationsYou need to know what the computer looks and sounds like when it’s operat-

ing normally so you have clues if it operates abnormally. Here we’ll talk about

three fundamental states of operation: startup and shutdown, sleep, and kernel

panic.

Startup and ShutdownDuring the startup process, the Macintosh looks for resources and reads those

resources with the goal of presenting a GUI. The GUI is the visual environment

users interact with to make the computer perform tasks.

NOTE � The word boot, short for bootstrap, is sometimes used to

refer to the process the computer uses to reach a running state. The

use of the word boot comes from the phrase “pull yourself up by your

bootstraps.”

Computer Operations 19

Startup Sequence Stage Cue

You may hear a click, fans or hard

disks spinning, or CRT crackling

Black screen, power LED on

Boot chimeBootROM—EFI� Metallic Apple: Found boot.efi.� Circle with slash: Could not load

boot.efi, or some other issue.

� Three beeps: No good memory banks.� Four beeps: No good boot images in

the boot ROM.� Five beeps: Processor is not usable.� Power LED flashes once per second =� Bad RAM, no RAM� Power LED continuously repeats a

series of three flashes and a pause =

Marginal RAM

BootROM—POST: POST runs diagnos-

tic on memory and processor

POST or BootROM failure� One beep: No RAM installed.� Two beeps: Incompatible RAM types.

Power On, Boot-ROM/RAM check

is initialized


Startup Sequence Stage Cue

Boot chime

Kernel Gray screen with Metallic Apple

and spinning gear

launchd Blue screen

loginwindow Login window appears.

User Environment Setup The text “Logging In” appears in

login window along with a progress

bar upon successful login. Desktop

and Dock appear.

Shutdown Process

In comparison to starting up, the process of logging out or shutting down is

simple. After a user selects Log Out, Restart, or Shut Down and confirms the

action, loginwindow quits all of the user’s applications and, if appropriate,

resets hardware and restarts or shuts down the computer.

BootROM—EFI� Flashing globe: Looking for

booter/kernel on NetBoot server.� Metallic Apple with spinning earth:

Found booter/kernel on NetBoot

server. � Folder with blinking question mark:

No bootable device has been found.


Startup Cues and Troubleshooting

Why do you care about the startup and shutdown processes? Because knowing

how the computer is supposed to start up, and what happens when it shuts down

gracefully, helps you when you need to locate and fix trouble (troubleshoot).

For example, suppose a customer complains that his PowerPC computer is

“freezing.” You have the customer restart the computer (to reset hardware as

appropriate) and describe what he sees and hears during startup. He describes

all the above cues including the desktop and Dock. He goes on to describe a

software application not responding when he launches it. From this informa-

tion you can isolate your initial troubleshooting to possibly user error or soft-

ware, eliminating OS and hardware.

In another example, suppose a customer complains because she wants to eject

a DVD at startup (she read that was possible), but she can’t get the computer

to respond as advertised. You have the customer step through the process and

notice that she doesn’t hold down the mouse button until after the spinning

gear appears. Why is this a problem? (Review the tables above to arrive at the

answer.)

NOTE � Although we’ve included some startup cues that show errors, if

you’re troubleshooting a computer that won’t start up properly, your best

bet is to check the service manual for the cues for that computer. Startup

error tones, beeps, etc., can change from model to model.

SleepHere is what happens when a computer goes to sleep.

On all computers:

� The microprocessor goes into a low-power mode.

� Video output is turned off, and the connected display may turn off or

enter its own idle state.

� Apple-supplied hard disks spin down.

� Third-party hard disks may spin down.


On PowerBook, iBook, MacBook, and MacBook Pro models:

� The Ethernet port turns off.

� Expansion card slots (such as PCMCIA, or Personal Computer Memory

Card International Association) turn off.

� The built-in modem (if present) turns off.

� An AirPort card, if present, turns off.

� The USB connection responds only to the power key on an external

keyboard.

� The optical media drive spins down.

� Audio input and output turns off.

� Keyboard illumination, if a feature of your portable computer, turns off.

Understanding how sleep operates will enable you to successfully troubleshoot

customer issues.

MORE INFO � For a more detailed description of how sleep operates,

refer to Knowledge Base document 25801, “Energy Saver: About sleep and

idle modes in Mac OS X.”

Kernel PanicUNIX-style operating systems, such as Mac OS X, may experience a type of

error called a “kernel panic,” which may provide information useful for soft-

ware developers.

A kernel panic is a type of error that occurs when the core (kernel) of an oper-

ating system receives an instruction in an unexpected format, or one that it fails

to handle properly. This error may also follow when the operating system is not

able to recover from a different type of error. A kernel panic can be caused by

damaged or incompatible software or, more rarely, damaged or incompatible

hardware.


In Mac OS a kernel panic should not be confused with an application freeze.

Instead of just one application no longer functioning, the entire system is no

longer operable.

Here is the onscreen dialog that a Macintosh system running Mac OS X 10.2

or later displays:

MORE INFO � For more detailed information on kernel panics, refer to

Knowledge Base document 106227, “What’s a ‘kernel panic’? (Mac OS X)”.

Cementing Key TermsReview the terms shown here and refer to Knowledge Base document 51908,

“Apple Glossary,” for any terms you do not understand.

ADC Administrator AGP AirPort-ready

AppleTalk Aqua Backup Baud

Bit Bitmap Boot/BootROM boot variable

bps Bus Byte Cache memory

Carbon Card CD-ROM CD-RW

Client Clock rate Cocoa Combo drive

Command Console CPU Crash or freeze


Cursor Daisy-chaining Darwin Data

Database Default Disk Driver

DVD-RAM DVD-ROM DVI Dynamic IP

Encoding Ethernet Extension FireWire

Font Footprint Fragmentation Frameworks

ftp Gigabyte (GB) Gigahertz (GHz) Graphics

accelerator

Hard disk/drive HFS HFS+ HTML

Initializing Installer IP address Kernel

Kernel panic Kilobit (Kb) Launch Log in

Logic board Math coprocessor Megabit (Mb) Megabyte (MB)

Megahertz (MHz) Memory Memory paging Modem

Monitor or display Mouse MPEG Multitasking

Nanosecond Network Open Firmware/EFI OpenGL

Operating system Partition PCI, EIDE, IDE PCMCIA or

PC Card

PDF Peripheral Pixel PostScript

PRAM Protocol Quartz QuickTime

RAM Reset switch RGB ROM

SCSI Startup device SuperDrive TCP/IP

Terabyte Terminal UDF UFS

URL Velocity Engine VGA and SVGA Video RAM

Virtual memory XML


Lesson Review1. Which three of the following constitute a basic computer system?

a. USB printer

b. Monitor

c. Processor

d. FireWire hard drive

e. Slots

f. Keyboard and mouse or trackpad

2. What is the “brain” of the computer called? Where is located?

3. To which form of memory must you save your work before the computer

is turned off?

4. Which form of memory loses information when the computer is

turned off?

5. Name and define the seven types of RAM that work with Macintosh

computers.

6. What is the basic difference between system software and application

software?

7. Describe the two ways in which Apple distributes software to customers.

8. Describe the three types of releases in which Apple distributes changes to

software.

9. What do we mean when we say a computer is booting?

10. What is the first resource used when a computer is powered on?

11. What is POST?

12. If you get a series of beeps at start up of an iMac G5 running Mac OS X

10.4 Tiger, which of the following has failed?

a. Power On

b. BootROM—POST

c. BootROM—Open Firmware

d. BootX


e. Kernel

f. launchd

g. loginwindow

h. User environment setup

13. If the computer stops responding with the spinning gear visible, where is

the computer in the startup sequence?

a. Power On

b. BootROM—POST

c. BootROM—Open Firmware

d. BootX

e. Kernel

f. launchd

g. loginwindow

h. User environment setup

14. What is visible when a Macintosh G5 or Intel-based system has started up

successfully?

a. A black screen

b. Flashing lights and LEDs

c. A metallic Apple

d. A gray screen with Apple logo and spinning gear

e. A blue screen

f. Login window

g. The desktop and Dock

15. When can you release the C key and still have a PowerPC-based

Macintosh start up from a CD?

a. A black screen

b. Flashing lights and LEDs

c. A metallic Apple

Cementing Key Terms 27

d. A gray screen with Apple logo and spinning gear

e. A blue screen

f. Login window

g. The desktop and Dock

16. Using the Apple Glossary (Knowledge Base document 51908) and the

material in this course, supply a definition and describe the troubleshoot-

ing relevance of each of the terms listed here:

Term Definition Relevance

Startup device

RAM

L2 cache

MHz

Frameworks

BootROM

Processor

17. Using the Apple Glossary (Knowledge Base document 51908) and the

material in this course, define the following terms:

Term Definition

Firmware

FireWire

Open Firmware

Kernel panic

Terminal

Combo drive


Term Definition

PC card

AirPort-ready

Dynamic IP

18. Here is an excerpt from a System Profiler report. What is the name of the

startup hard disk?

—————————————————————————-

System Profile

—————————————————————————-

Software Overview:

+———————————————————————————————————+

| |

| System version : Mac OS X 10.2.6 (6L60) |

| Boot volume : Macintosh HD |

| Kernel version : Darwin Kernel Version 6.6: Thu May 1 21:48:54 PDT 2003;

root:xnu/xnu-344.34.obj~1/RELEASE_PPC |

| User name : Elizabeth Gharity (elgy) |

| |

+———————————————————————————————————+

Hardware Overview:

+———————————————————————————————————+

| |

Lesson Review 29

| Machine speed : 800 MHz |

| Bus speed : 100 MHz |

| Number of processors : 1 |

| L2 cache size : 256K |

| Machine model : PowerMac4,5 (version = 2.1) |

| Boot ROM info : 4.4.5f3 |

| Customer serial number : QT23493E-N0S-ff12 |

| Sales order number : Not available |

| |

+———————————————————————————————————+

Memory Overview:

Location Type Size

DIMM0/J22 empty

DIMM1/J20 SDRAM 256 MB

Mac OS X

Macintosh HD

Darwin

elgy

Answer Key

1. b, c, f; 2. Processor, main logic board; 3. Memory that doesn’t require power,

for example, a magnetic drive or an optical drive; 4. Memory that requires

power, for example, RAM like SO-DIMM or SDRAM;


5.

RAM Type Definition

DIMM (dual inline memory module) Larger capacity and faster than

SIMM (single inline memory module)

More expensive due to smaller

packaging

SDRAM (synchronous dynamic RAM) Internal clock synchronized

with processor clock for better

performance

VRAM (video RAM) Same as DIMM but dedicated to

video output and processing

SGRAM (synchronous graphics RAM) Synchronizes with the graphics

processor for better performance;

same as SDRAM

Doubles the memory chip’s data

throughput, consumes less power;

also called SDRAM II

Memory design from Intel that uses

serial communication between the

FB-DIMM and the memory controller

6. System software is used to start up the computer environment and provide

the GUI for the user. Application software is used to start up a program envi-

ronment and is most commonly associated with tasks a user wants to accom-

plish, such as making a DVD; 7. Software is released in a standalone package

or bundled with a computer. Standalone software can be distributed online

(as a download) or in a box through retail channels. Bundled software is dis-

tributed with a computer and is usually preinstalled (installed at the factory);

FB-DIMM (fully-buffered dual

inline memory module)

DDR-SDRAM (double data rate

synchronous DRAM)

SO-DIMM (small outline dual

inline memory module)

Lesson Review 31

8. Software is released as a reference release, independent from previous

versions; as an upgrade, which delivers new features; and as an update, which

delivers software improvements and bug fixes. Most of the time, we can use

version numbers to determine whether the software is significantly different

from another version; 9. Although the computer science definition of boot-

ing is pretty technical, for our purposes, when we talk about booting, we’re

talking about the Macintosh startup process that starts from pressing the

power button and ends (when it’s successful) with the display of the desktop

and Dock; 10. When a computer is first powered on, it accesses the BootROM;

11. Power On Self Test (POST) is a diagnostic run when the computer is first

powered on to make sure the computer processor and memory are function-

ing properly. If everything checks out OK, the computer will chime and the

startup process will continue. If POST fails, the startup process ends with an

error tone and/or power LED flashes; 12. b; 13. e; 14. g; 15. d;

16.


Startup device You must be able to

identify the startup

device to troubleshoot

OS-related problems

RAM Random-access memory A common source of

poor performance or

other troubleshooting

issues

L2 cache A common metric of

performance and

source of customer

questions

Fast RAM on separate

chips located on the same

board as the processor and

connected directly to the

processor through its own

high-speed bus

The device, typically a

hard disk, that contains

the valid OS



MHz A common metric of

performance and

source of customer

questions

BootROM Useful for trouble-

shooting startup

problems

Frameworks An integral part of

Mac OS X that is

very different from

Mac OS 9 and earlier

Processor A common metric of

performance and

source of customer

questions

17.

Term Definition

Firmware Software (programs or data) that has been written

onto read-only memory (ROM); a combination of

software and hardware

Central processing unit

(CPU); in current Power

Mac, Mac Pro, Mac mini,

iMac, PowerBook,

MacBook Pro, MacBook,

and iBook computers, the

processor is a PowerPC

G4, G5, or Intel chip

Types of bundle that pack-

ages a dynamic shared

library with the resources

that the library requires,

including header files and

reference documentation;

used by Mac OS X

Read-only memory

(ROM) that contains

system command sets

Abbreviation for megahertz;

the speed of microprocessors

Lesson Review 33

Term Definition

FireWire Apple’s cross-platform implementation of a high-

speed serial data bus (defined by IEEE Standard

1394-1995) that can transfer large amounts of

data between computers and peripheral devices

Open Firmware A cross-platform firmware standard for

controlling hardware; used by all PCI-based

Mac OS computers

Kernel panic Type of error that occurs when the core (kernel)

of an operating system receives an instruction

in an unexpected format or one that it fails to

handle properly

Terminal A Mac OS X application that lets you use a

command-line interface and BSD (a version of

UNIX developed at UC Berkeley) utility programs

Combo drive An optical drive that writes CD-R discs, writes

CD-RW discs, reads DVD-ROM discs, and reads

CD-ROM discs

PC card Short for PCMCIA (Personal Computer Memory

Card International Association) card, a small,

credit card-sized device originally designed for

adding memory to portable computers

AirPort-ready A Macintosh computer with AirPort antennae

installed and a slot that accepts an AirPort Card

Dynamic IP Enables a device to have a different IP address

every time it connects to the network

18. Macintosh HD


computer basics

Documents

macintosh computer

basic computer theory

computer system

processors processors

abnormal computer operation

basic physical components

types of processors

basic elements