How Computers Work – Course Information



HS Computer Hardware Outline Week #7

Computer Cases

Expandability

Getting Your Hands in There

Protection

Longevity

Switches

Power

Reset

Keylock

LEDs

Power

Hard Drive

Case Styles

Desktop

Slimline

Tower

Full Tower

Mid Tower

Mini Tower

Form Factor

AT

ATX

Mini ATX

Micro ATX

ESD – Electrostatic Discharge

How Much is Too Much

ESD and Your Computer

ESD Damage

Immediate Failures

Latent Failures

Antistatic Wrist Straps

Antistatic Mats

What Else?

Online – Your Computer’s Case

ESD – Electrostatic Discharge

Homework - Online Case and ESD Quizzes

Your Computer’s Case

Your computer's case plays a large part in the overall expandability, protection, cooling and lifetime of your system.

Expandability

At one time or another you may decide to add something to your computer, such as a DVD Player, a second Hard Drive, a Memory Card Reader, or a Tape Drive. These fit on shelves in your computer called Bays. If there are no extra bays, then there’s no place for these devices to go. These bays can be 3.5 inches or 5.25 inches wide. There are internal and external bays. You can notice the external bays by looking at the front of your case.

Devices like Memory Card Readers and DVD drives slide into external bays and can be seen (and accessed) from the front of your system case. If you have unused bays, they will have a plastic faceplate over them (or at least they should have). If you see that you have empty external bays, then you know that at least there's room to add another of this type of device. Remember however, that hard drives are sometimes hidden behind these faceplates, so a look inside the case will tell you for sure. Hard drives are generally situated in internal bays because there is no need for physical outside access. You must look inside the case to see if you have any free internal expansion bays.

Any device added to your system requires power, and your power supply has to have enough juice to supply that power. If you have a 150 or 200-watt power supply, your system may be limited to the amount of devices that can be added. Most cases come with a power supply, but make sure.

Getting Your Hands in There

You may at one time or another, have to remove, change or check a device in your computer. You want to be able to access that device without too much difficulty. It would be nice if you didn't have to remove the ribbon cables and expansion cards just to install another memory module, or replace a battery. Or, if you're the type that likes to just jam his hand in amongst all that stuff, it would be nice to be able to remove it without accidentally loosening or removing other connections.

On some cases you can loosen a single screw, and completely remove the drive bays for easy access to the drives and their mounting screws. Others have access ports for the screws on the back plate of the case. However, I’ve seen some drive bays that are spot-welded in place without access ports, and you just about have to remove the motherboard to access the screws for the drives. Think about what you want to put inside and make sure there's enough room for access.

Protection

A good, rigid, well built case can protect the internal components from dust, vibration, foreign objects, ESD (Electro Static Discharge) and EMI. Electromagnetic interference is not always an easy one to nail down. My computer has a good solid case, but when you watch TV, you can tell if the computer is on or not.

You can find cheap cases that fit together so poorly, or are so flimsy, that they actually rattle when the computer is turned on. One thing that can be bad for your system are vibrations caused by outside sources; whether it’s a panel or cover that rattles, a desk drawer being closed, or a printer that doesn’t operate the smoothest. The stability of the case makes a big difference.

Some of the case frames are left unfinished, resulting in sharp edges, burrs and metal slivers. Ribbon cables and wires (and your fingers) can be nicked or cut by these sharp edges just by removing or replacing the outside cover. Companies that actually put some research and development into their product will address these issues. You should think about them when you purchase. As with just about everything, you usually get what you pay for.

Longevity

Heat shortens the life of electronic components. The different devices and components inside your case need room to breathe and release heat build-up. Sometimes, things are packed so tightly inside your system case that you can’t even get your hand in to remove a cable or an expansion card, let alone allow for any kind of air flow. Air flow is needed to cool down the components and devices inside the case.

The cooler that your computer operates, the longer it will last. The fan on the power supply is made to help cool the power supply as it operates. The way the case is built should allow the intake of cooler air through vents, draw it over the different components inside to help cool them, and push the heated air out. Some cases come with auxiliary fans that fit over the intake vents to add to the airflow inside.

It’s important not to interrupt this flow. Don’t pack things around the case or obstruct the intake vents. Keep the intake vents clean and clear of grime and dust balls. Also, by leaving the expansion slot inserts off the back of the case, or the faceplate off unused external bays, you could possibly be changing the way the air flows through your case and reducing cooling efficiency.

If you have a system that seems to run fine, then just shuts itself off after a half hour or so, check out the operating temperature of the CPU. See that the fans are working on the power supply and the CPU's heatsink.

Switches and LEDs

If you look at the front of your case you can see the devices that are installed in the external bays and get an idea as to how many unused bays you have. You will also notice one or more switches and LED lights.

Power switch

To start your computer, you have to turn on the power supply. At one time, the power switch for your computer was on the power supply itself, and you had to reach around to the back of your computer to turn it on and off. This was inconvenient, troublesome, and a real pain in the …neck. Most cases today have a remote power switch on the front of the case.

Reset switch

When you first start your computer, it goes through a series of self-tests (POST - Power-On Self Test) before it actually initializes itself and starts up the operating system. The reset switch performs the same function as a warm boot (ctrl+alt+del) which restarts your computer with an abbreviated version of POST, taking a little time off the startup process. With Win95/98’s restart option on the Start menu, today’s computer cases may or may not have a reset switch.

Keylock switch

Most new cases don’t have a Keylock switch. By inserting and turning a key in this lock, you could shut off access to the keyboard, thus denying unwanted users from accessing your computer or preventing an accidental keystroke from interfering or interrupting a currently active program. These are still found on network servers.

Power LED

This light tells you when the power is on to your computer.

Hard Drive LED

This light will go on, or flicker, every time your hard drive is written to or read from. It lets you know whenever the hard drive is being accessed.

Each device installed in a case’s external drive bay (floppy drive, CD-ROM, tape drive, etc.) will usually have its own indicator LED on the front bezel that will come on or flicker when that device is being accessed.

The back of your computer will have holes and slots cut into the frame. These holes allow for the back of expansion cards and any I/O ports that your external devices can plug into. Any slot or hole that is empty should have a cover on it. These are easy to distinguish from any venting holes that might be on the back of your case (venting holes should not be covered). The back of the power supply will also be exposed here showing you the power supply fan vent and the plug for the power cord.

Case Styles

Basically, there are two different styles of system cases today; The Desktop and the Tower.

The desktop case sits flat on the top of your desk with the monitor situated on top. This was the style of IBM's original PC, XT and AT models. These early desktops were fairly large and bulky, taking up a lot of real estate on the desk. The obvious trend was for manufacturers to make them smaller and more compact. Unfortunately, as you make the case smaller, things inside get a little crowded. Access to the different components becomes much more cramped, cooling is a lot less efficient, and there's less room for expansion. Desktops usually have two or three external drive bays and 1 or 2 internal bays. 

The slimline case is even smaller. It's shorter, narrower, and looks a lot less bulky on your desk. This is about the only appeal these machines may have. Slimline computers are very proprietary, not well cooled at all, and have about zero room for expansion. Slimlines usually have one or two external bays and one internal.

The tower case sits on end, taking up less square area space and offering a better variety of sizes than a desktop. It allows for a lot more choice as to location, depending of course on the particular size. It can sit on the desk beside the monitor, on a separate shelf, or on the floor beside the desk.  On the negative side, it should be mentioned that cases on the floor may be more prone to kicks and bumps and in some locations the cords may have to be extended. Tower cases have much better air flow, better accessibility to internal components, and (except for the micros and ultra low end  models) allow for more upgrade and expansion capability. 

Full Tower

-largest, up to 36" high

-sits on floor

-larger power supplies, 350 watts or more

-may have 2 X 3.5" and 4 or more 5.25" external bays

-may have 4 or more internal drive bays

-very roomy inside, better cooling

Mid Tower

-power supply - 200 - 300 watts

-quite popular size

-approx 17-20 inches in height

-2 X 3.5" and 3 X 5.25"external drive bays

-2 or 3 internal drive bays

-less room than a full tower to work inside

-still cools really well

-still room for expansion

Mini Tower

-very popular size

-smallest of the tower cases (...sub-mini and micro?)

-can be less than 14 inches high

-power supply 200 to 250 watts

-cools better than a desktop case (but not much)

-2 X 3.5" and 2 X 5.25" external drive bays

-1 or 2 internal drive bays

-a little cramped inside

Note: The sub-mini and micro size cases are actually smaller than the mini tower. These cases have 1 or 2 external drive bays and only 1 internal bay. The sub-mini and micro are targeted at the low end computer market and usually have very limited possibility for upgrade and no room for expansion.

Remember too, that there can be some pretty fine lines between the different case styles. One company's mid-tower might be another company's midi-tower. One might take out a single 5-1/4" bay, and call it a mini-tower, whereas the next manufacturer may still refer to it as a mid-tower.

Form Factors

Cases come in different sizes and styles, and so do motherboards. The size and shape of the circuit board, the position of the components, the position of the screw holes, and the technology incorporated make up a motherboard’s form factor. If you buy a new computer, it’s not really a problem because the system board is already in the case. But, if you're building a computer, or buying a new case for a computer, then you have to be sure the case will accommodate the motherboard’s form factor. The case gets its form factor name based on the form factor of the motherboard that it will accommodate.

ATX - The ATX motherboard has the different I/O connectors, serial, parallel, and USB ports hardwired directly to the motherboard in a small cluster at the back of the computer. The power switch on the ATX case is connected to the motherboard, not directly to the power supply, and there is power to the board at all times. The cases come in all the regular sizes and styles. The ATX is currently the most popular form factor out there.

There is a slightly smaller version of the ATX called the Mini ATX. Although the motherboard is slightly more compact, it uses the same case and power supply. I mention it here, only to differentiate between it, and the Micro ATX.

The more compact version of the ATX is called the Micro ATX, and it's targeted toward the low end computer market. The cases generally have about 1 X 5-1/4" bay, 1 X 3.5", and 1 internal bay. The Micro ATX power supply is also smaller, and usually has just enough power for what's already in the computer. There is very little (zero) room for expansion. I think the Micro ATX probably came about as a result of manufacturers competing for that first 'under $1000' computer.

ESD - Electrostatic Discharge

    ESD is simply the discharge of built up static electricity. Electrostatic discharge however, should not be taken lightly when working with computers. ESD has the capability of causing enough damage to the components inside your computer to render it completely inoperable. It's important to use an anti-static strap and/or a grounding mat whenever working on the inside of your computer. Being aware of ESD precautions can significantly reduce the chance of damage to your computer due to static electricity.

   Static electricity is a fact of Life. You're producing it and discharging it constantly. Moisture in the air can help it to dissipate, and raising the humidity in your workplace is another very good measure you can take to reduce the chance of damage caused by ESD. ESD is bad for computers and electronic components. If you are opening the case or working inside a computer, always take ESD precautions.

How Much is Too Much?

    Have you ever walked across a carpet on a dry winter day, touched somebody, and heard the snap of electricity as a small blue spark jumped from your fingertip to the edge of your victims ear?

    If the discharge was felt, it was probably more than 2000 volts. If you heard it, then it could have been between 3000 - 5000 volts. If you actually saw a small blue spark, it was more than likely in excess of 10,000 volts.

    So do I have to walk on a shag rug? Does it have to be a dry winter day? No! Your body is building up and discharging static electricity all the time. Just shifting in your chair can produce up to 150 - 200 volts! You can't completely eliminate this problem but it can be controlled.

ESD and Your Computer

    The ICs (Integrated Circuit chips) on the various circuit boards in your computer use between 2 - 5 volts. They can be damaged by less than 200 volts. Some may be damaged by as little as 30 volts. This means that ESD can cause damage to the various components inside your computer and you won't feel it, hear it, or see it. In fact, the discharge voltage could be 1000 times less than what the human body can feel!

     When they started replacing the tubes in radios with transistors, people were amazed at how small radios were getting. You could get a transistor radio that boasted 7 transistors and was about the size of a brick! …Today, some of the individual chips on your computer's circuit boards contain millions of transistors. Advancements in technology allowed for entire circuits to be etched onto a single chip. These are called Integrated Circuit Chips.

     One technology for producing ICs is called TTL (Transistor Transistor Logic). These chips are actually more tolerant of ESD and even faster than the newer technology. However, they're also larger, use more electricity or power, and their resistance causes them to run very hot. As computer technology advanced and the number of transistors in the chips increased, heat and power consumption became a huge problem.

     TTL ICs are still used in computers today, but the newer CMOS chips (Complimentary Metal-Oxide Semiconductor) have all but replaced them entirely. These chips have a semi-conductive metal oxide layer that allows for less resistance, reducing the power consumption and the generated heat.   Unfortunately, the very technology that makes these CMOS chips more efficient also makes them very susceptible to electrostatic discharge.

    Wait a minute! If you can discharge 10,000 volts of static electricity into somebody's ear, how come it doesn't kill them? Well, the amperage is very low. The human body is very tolerant of voltage, it's the amperage, or a current's strength, that will kill you. The chips inside your computer however, are highly sensitive to any kind of voltage, even at very low amperages.  ...By the way, all of today's CPUs (Central Processing Units) and system memory chips on your RAM modules are CMOS chips.

ESD Damage

    So what kind of damage can be caused by ESD? Anything from a simple system interruption, causing your computer to reboot with no further problems, to complete destruction of a chip that will make your system unusable until the chip is replaced. Also, you won't find any discoloration, burn mark or physical indication whatsoever as to which chip has been damaged.

    There are 2 types of damage that can occur:

Immediate Failures (Direct Failures, Catastrophic Failures) - These are failures that occur immediately after the chip has been damaged and usually aren't recoverable until the chip has been replaced. Say you open your computer (or worse yet, someone else's) to install more memory. Without using an anti-static strap or a grounding mat (you've done it lots of times before and never had a problem), you take a brand new RAM module from its anti-static packaging, install it, and now the computer won't even finish its boot sequence. Not a good situation, but you do know the computer worked before you installed the RAM, so you should have an idea where to start looking for the problem.

Latent Failures (Upset Failures, Delayed Failures) - Sometimes a chip can be damaged by electrostatic discharge and the results aren't immediately noticeable. Months later the chip could finally fail completely, or you may end up with intermittent failures that occur sporadically. These are usually difficult to attribute to any specific cause, and very hard to track down.

Although static buildup can’t be completely eliminated, there are precautions you can take to reduce the possibility of damaging components due to electrostatic discharge. You should always ground yourself to discharge any static buildup before touching anything inside your computer’s case.

Antistatic Wrist Straps   

An excellent way to prevent ESD damage to your computer is to use an anti-static wrist strap. It’s a conductive strap that fits on your wrist as you’re working. It has a wire attached to it with an alligator clip on the end to connect to your case or to an anti-static mat. Some can be plugged right into the wall socket. Only the ground receptacle makes contact. But make sure the cord is long enough, unless you have a receptacle right at table level. If you’re working inside a computer’s case, the most important tool you should have is an anti-static wrist strap.

At the very least, you should use an anti-static wrist strap connected to the bare, unpainted metal of your case’s frame. There are two schools of thought on this subject:

1.    One is to leave your computer plugged in. Any static buildup is discharged along your wrist strap to the computer's case, then through the power cord into the ground receptacle of your electrical outlet.

2.   The second is to unplug your computer. With the wrist strap attached, this should put you and your computer at the same potential charge and no transfer of electrons should take place.

    This becomes a decision you have to make for yourself. A lot of books will suggest that the computer remain plugged in, and in fact, the A+ Certification exam considers this the correct choice at this time (which is probably why these books suggest it). However, when you leave the computer plugged in, it’s a little too easy to turn it on when you’re working inside; or forget it’s on and plug in an expansion card or drop a screw onto the motherboard. Also, you have full AC power going to the remote power switch on the front of your computer. If there is a bared wire, or open contacts on the back of the switch, you could get quite a shock. Remember too, that today’s ATX motherboards have power to them even when the switch is off.

A very good alternative is to plug your wrist strap right into the ground receptacle of a wall socket, or into a grounded antistatic mat.

Antistatic Mats

    Antistatic mats provide a grounded surface on which to work or place components as you remove them. They also have a cord that can be plugged into a wall outlet to slowly remove any static charges. Some come with another cord and a clip that attaches to your computer’s case. The computer does not necessarily have to be on the anti-static mat when you’re working on it. If the mat is plugged into a wall socket then it’s grounded. Attach an alligator clip from the mat to the case, and now the case is grounded. Attach your wrist strap to the case, and now any static buildup can be safely discharged from your body. As you are working, any parts you remove or plan to install can be safely placed on the anti-static mat.

    If you find yourself in a situation where you don’t have a grounding mat or anti-static wrist strap, then you should keep one hand on a bare, unpainted portion of the chassis as you’re working inside the case. This method is not that reliable and you’ll soon find it to be a little awkward. The ten or twelve dollars spent on a good wrist strap is a wise investment.

What else?

    Don't work on a computer or components when they are cold. Allow them to warm up to room temperature first. Cold, dry conditions promote static electricity. In the winter, when it's very dry, static can build up very quickly. Raising the humidity in your workplace can help to dissipate this buildup. Humidity at 50% to 60% is ideal.

    Keep components and expansion cards inside their anti-static bags until you are ready to use them. Remember to handle them carefully, by their edges and as little as possible. Anti-static bags are treated to be conductive so that they draw static away from the components inside. It's always a good idea to keep a supply of anti-static bags to put expansion cards and components into when working on a computer.

    It's better to have a tile floor in your work area than rug or carpet, which promotes static buildup. Also, think about what you wear. You don't want to be working inside your computer while wearing a wool sweater or a nylon jacket.

    You may not be able to take every ESD precaution all of the time, but use your head and do what you can. The components and hardware inside your computer are subject to electrical fluctuations, spikes, surges, power losses, temperature extremes and, I suppose, even physical abuse. But, the number one cause of damage to internal components is Electrostatic Discharge.

System Case - Review

1. If you have a PC case that can be opened without the use of tools, then it is probably a ________ .

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[pic]screwless case

[pic]screwed case

[pic]SnapLok case

[pic]SnapTite case

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[pic]2. The areas in your computer's case where you would install drives are called internal and external ______ .

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[pic]compartments

[pic]trays

[pic]bays

[pic]bezels

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[pic]3. A/An ___________ format motherboard has power supplied to it

even when the computer is off.

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[pic]ATX

[pic]Baby AT

[pic]NLX

[pic]XT

4. Your computer's case doesn't just store the motherboard and CPU. It also has a lot to do with the _______________. (choose all that apply.)

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[pic]expandability of your system.

[pic]accessibility of different parts and devices.

[pic]protection of your system.

[pic]lifetime of your computer system.

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[pic]

5. The different expansion bays in your computer's case are normally

__________ and ________ inches in size.

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[pic]3.25, 5.5

[pic]5 1/2, 3 1/4

[pic]3.5, 5.25

[pic]6, 4

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[pic]

6. IBM's original PC and XT computers sat flat on your desktop with the monitor on top. This is an example of the early _______ style of case.

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[pic]tower

[pic]slimline

[pic]tabletop

[pic]desktop

7. A good, rigid, well built case can protect the internal components from ____________ .

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[pic]dust

[pic]vibration

[pic]electronic interference

[pic]all of the above

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[pic]8. A computer's case is supposed to be designed so that air flows over the different components inside to help cool them down.

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[pic]True

[pic]False

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[pic]9. This computer case is the largest of the tower style cases. It has lots of room for expansion and easy access to components.

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[pic]Full Tower

[pic]Mid Tower

[pic]Mini Tower

[pic]Slimline

10. This tower style case is one of the most popular. It cools better than a desktop style case but tends to be a little cramped inside with only 1 or 2 internal drive bays.

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[pic]Full Tower

[pic]Mid Tower

[pic]Mini Tower

[pic]SlimTower

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[pic]11. The size and shape of the circuit board, the position of the components, the position of the screw holes, and the technology incorporated, make up a motherboard's ____________.

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[pic]Configuration

[pic]factory specs

[pic]form factor

[pic]OEM factor

Electrostatic Discharge - Review

1. Shifting in your chair can produce up to _______ volts.

o Top of Form

o 2000

o 10,000

o 3000 – 5000

o 150 - 200

2. When servicing a PC, where would you attach the ground strap to prevent ESD? (Check all that apply.)

o Top of Form

o To the inside of the case

o To the static shielding bag that came with the computer

o To the ground mat

o To the PC's power supply

3. ESD is an acronym for:

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o Electronic Static Discharge

o Electrostatic Device

o Electrostatic Discharge

o Emergency Startup Device

4. Antistatic bags are treated to become ____________.

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o Non-conductive

o Conductive

o Corrosive

o Non-alergenic

5. Latent Failures are

o Catastrophic

o Failures that occur immediately

o Delayed failures

o Direct Failures

6. Which one of the following does not help prevent ESD?

o Antistatic Wrist Band

o Antistatic Mat

o Antistatic Bag

o Raising the humidity

o Making the room colder

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