Figure 21-3: Computer case elements ©2004 Barry Press & Marcia Press Desktop PC cases come in a range of sizes, from small ones with limited expan- sion capability to floor-standing monsters able to hold multiple systems. It’s important to think through the expansion you might want to do before you buy a new case or new complete system because it’s going to require drastic measures if you want to exceed the space or cooling available in the case. The size of the case also affects how hard the system is to work inside because small cases are almost always cramped and hard to work with and tend to force haphazard cable layouts that themselves complicate access and service. Large cases are much easier to work with, have more expansion capability, and have better airflow to aid cooling, but aren’t as easy to fit into your office, home, or home theater. I/O Processor (under fan) 5.25-inch external drive bays Memory DVD writer Power supply PCI and AGP bus Video card (display) 3.5-inch external bays Disk drives 332 Part VII ✦ Integration Airflow and heat buildup Airflow cools nearly every desktop computer sold today and is created by fans in the case itself and in the power supply. How much air pressure the fans cre- ate and how much air resistance the components and the shape of the case create determines how effective the cooling will be. Very small cases with lim- ited airflow may be incapable of cooling faster processors, video cards, and disks that generate a lot of heat. We measured the power consumption and temperature rise in three different systems to see how effective their fans and cases were at removing heat. Table 21-1 shows the results of those measurements. System A was a full-size tower, System B a mini-tower, and System C a full-size tower with auxiliary fans to improve airflow. System D is the PC you’ll see how to build in Chapter 25. Degrees per watt (the right-hand column in the table) is the measure of how well a case cools the electronics inside, measuring how much the exhaust air temperature of the case will climb over the inlet temperature per watt of power dissipated inside the case. Table 21-1 Cooling Performance Comparison (In Degrees Centigrade) System Inlet Exhaust Rise Average Power Degrees Consumption (W) per Watt A 20.0 33.1 13.1 96.0 0.1366 B 21.9 30.7 8.8 46.8 0.1887 C 20.0 21.9 1.9 68.4 0.0276 D 18.6 30.8 12.2 149.4 0.0818 Systems A and D consume the most power and therefore generate the most heat. The airflow from the power supply fans is the only cooling Systems A and B have, while Systems C and D both have an auxiliary exhaust fan in addition to the power supply fan; System D controls the fan speeds based on measured temperatures. The temperature rise from the System C or D inlet to exhaust is less per watt than in Systems A and B because the cases are larger, with fewer restrictions on airflow, and because the auxiliary fan helps move more air. Cooling All PC processors should have cooling fans on the chip. A processor cooling fan assembly includes both a heat sink and a fan, as shown in Figure 21-4. The processor cooling fan gets power from either the motherboard or from a tap on a disk drive power connector. Heat created by the operation of the chip Chapter 21 ✦ Cases, Cooling, and Power 333 flows from the chip to the surrounding chip package. The heat sink (a finned structure clipped into close contact with the chip package) conducts heat from the chip package, removing heat from the chip and keeping it cooler. Cool air driven past the heat sink by the fan takes heat off the heat sink into the surrounding air. The fins on the heat sink increase the contact between the air and the heat sink, improving the rate of heat transfer. If the fan stops, however, little or no air moves, and the rate of heat transfer slows greatly. The chip will get hotter until its maximum ratings are exceeded. At that point it will fail, possibly permanently. Figure 21-4: The fan drives air past the fins on the heat sink, cooling the fins and heating the air. Heat sink Fin Processor chip Fan Heat flow Heat flow 334 Part VII ✦ Integration Checking Your Processor Fan Installation Here’s how to find out if your processor cooling fan is working right, and if it’s mounted on the chip properly. (Be careful about discharging static electricity; see Chapter 1 for the right techniques.) 1. Turn off the computer, open it up, and unplug the processor fan. 2. Power up the machine and keep a finger on the fan’s heat sink. If the chip and heat sink are in good contact, the heat sink will get very hot. 3. Quickly shut down the machine, reconnect the fan power, and start up again. Let the chip temperature stabilize by waiting a few minutes, and check the heat sink temperature with your finger again; you’ll see that it’s a lot cooler. Don’t leave the power on with the fan unplugged for more than a minute or so, or you’ll cook the chip. Also, this test may not work with every motherboard, because some boards detect low RPMs from the processor fan and refuse to boot in that case. Figure 21-5 is a close-up of the processor cooling heat sink and fan we used in the high performance PC you can see how to build in Chapter 25. It’s rated to cool even the 3.2 GHz Pentium 4 processor, and does so without creating a lot of fan noise because of the large copper heat sink. The overall assembly exceeds Intel specifications for maximum heat sink weight, however, so you’ll have to take precautions if you intend to ship the computer after assembly. Figure 21-5: Processor cooling heat sink and fan ©2004 Barry Press & Marcia Press If you look at the specifications for commercial-grade chips, you’ll find that they are commonly rated for a “free-air temperature” of up to 70 degrees Celsius (158 degrees Fahrenheit), far above the exhaust air temperatures in Table 21-1. The limited airflow created by weak fans in most computers lets heat pockets build up in the case, causing the air temperature in the vicinity of the pocket to go well over the maximum ambient rating. Figure 21-6 shows one way heat pockets come about. A stack of disk drives and other peripherals is common in most computers. Each drive includes both a drive mechanism and a board of electronics, both of which generate heat that gets trapped in the pockets between drives and boards. Stacking drives one on top of another tends to block the airflow, forcing most of the cooling air to flow around the sources of heat. This allows heat pockets to develop in the stack, as shown in the exploded view of the floppy drive and CD-ROM drive on Chapter 21 ✦ Cases, Cooling, and Power 335 the right of Figure 21-6. If the air temperature in the pockets exceeds maximum ratings, the drives will fail. The example in Figure 21-6 happens all the time. You can solve the problem by making sure the case you use has a metal cage surrounding the drives that conducts heat away (plastic ones can’t do that) and by making sure the sides of the drives have solid, metal-to-metal contact with the cage. If you mount 3.5- inch drives in 5.25-inch bays, make sure the spacer brackets you use are metal and themselves provide a good heat conduction path. Figure 21-6: Trapped air in the case can overheat chips and cause failures. Pockets of trapped heat can happen in a group of adapter cards plugged into the motherboard, too. Each card generates heat — graphics cards in particular — and the tight spaces between cards can impede good airflow. Figure 21-7 shows the normal airflow pattern in a tower or mini-tower case — the airflow runs from inlets on the front, past the motherboard and cards, and out through the power supply and vents in the back. A little air comes in from openings at the front of the drive bays and is drawn to the back, but not much unless you explicitly use a drive fan with front inlets. The horizontal position- ing of the adapter cards can trap heat too, so the relative position of cards is worth some thought — you should leave gaps between cards to keep hot cards away from each other if possible, and order cards to prevent having two hot cards in adjacent slots. Open space helps avoid blocked airflow. Bigger fans or more fans move more air through the case, lowering the internal case temperature, which helps to overcome blockages and heat pockets. Badly placed cables can block airflow. Hard disk Drive bay stack A i r f l o w Heat pockets Floppy drive CD-ROM drive Tape drive Hard disk Drive mechanism Drive electronics Drive mechanism Drive electronics 336 Part VII ✦ Integration Figure 21-7: Tower case airflow The ATX form factor The IBM PC/AT established a motherboard form factor that survived for over a decade. As component technology and system designs evolved, though, prob- lems with that design became more onerous. Four of the more significant prob- lems were as follows: ✦ Processor positioning — The processor on an AT motherboard typi- cally sits under the space reserved for some of the adapter cards. Processor cooling fans would intrude into the space for the cards, preventing full-length cards from being used in those slots. ✦ Lack of low voltage power — The chips used when the AT mother- board was designed all used 5 V power, and the AT power supplies were specified for that interface. The small line widths now in proces- sors and other chips require 3.3 V, 2.0 V, or less, because they can’t withstand the higher voltages without conversion. ✦ High voltage switching within the computer case — The PC/AT was a desktop unit that positioned the power switch inside the power supply, but on the side of the case at the back. That’s inconvenient for tower cases, which led designers to move the high voltage power switch to the front of the case. The presence of high voltage within the case can be a hazard. Drive bay #1 Drive bays Side view Front viewAdapter cards Airflow Motherboard Power supply Drive bay #2 Drive bay #3 Chapter 21 ✦ Cases, Cooling, and Power 337 ✦ I/O port cabling requirements — The PC/AT had no I/O ports built onto the motherboard. As the functions built onto motherboards expanded to include serial, parallel, sound, mouse, Universal Serial Bus (USB), and network ports, cables had to be built to route the sig- nals from the motherboard to the front or back of the case. The labor involved has led to the building and installing of those cables becom- ing a noticeable fraction of the system cost. The need to solve these problems in the AT motherboard form factor led to the definition of the ATX form factor incompatible with the older AT layout. The most apparent characteristic of an ATX case is the input/output (I/O) panel at the top of the motherboard (see Figure 21-8). Figure 21-8: The ATX form factor simplifies internal cabling and improves component layout. ©2004 Barry Press & Marcia Press The ATX form factor improved PC designs in several ways: ✦ Processor positioning — The processor in an ATX case is behind the I/O panel, out of line from the adapter cards. That repositioning pro- vides clearance for fans above the processors. The memory sockets have been relocated near the processor to simplify motherboard design. ✦ Lack of 3.3 V power — Initially, the power connector on an ATX motherboard included 3.3 V along with the usual ±5 V and ±12 V supplies. As processor power requirements increased, the interface expanded to include an auxiliary 3.3 V connector to provide addi- tional power. Current generation processors require more current than can reasonably be sourced directly from the power supply — the 3.2 GHz Pentium 4 Processor Extreme Edition can consume 71.5 A at 1.475 to 1.55 volts — and therefore use the modified ATX12V power supply specification, which adds a third motherboard connector sup- plying 12 V to be stepped down on the motherboard. 338 Part VII ✦ Integration ✦ High voltage switching within the computer case — The power sup- ply in an ATX system is more like an instant-on television than older computer designs. The power connector to an ATX motherboard also includes a low-voltage signal that gets routed to a power on/off button on the front of the case. That signal tells the power supply to turn the main supply lines on or off. As long as power is connected, though, the motherboard receives a limited 5 V supply to keep standby func- tions running. Standby power makes it even more important to disconnect an ATX supply from wall power whenever you’re working inside the case. ✦ I/O port cabling requirements — The I/O port connectors are built onto the ATX motherboard, terminating in a panel at the back. A standard layout for the panel exists, ensuring cutouts in the case will be in the right place. Demand has lead to designs for smaller desktop PCs. The NLX form factor, available in the late 1990s, made small boxes possible, but never caught on. Later designs from Shuttle and Soltek have been well received, but used moth- erboards and cases built to a proprietary form factor. The Intel BTX specifica- tion includes a profile for a relatively small PC, but it’s as yet unclear if it will supplant ATX and microATX. Choosing a case Although laptops and very small form factors leave few choices but proprietary designs, keep in mind that, despite all the competition in the PC industry, need- lessly proprietary designs remain a favorite tactic of companies hoping to lock you in for expensive upgrades once you’ve bought their product. Lots of companies use this tactic — a who’s who of the PC industry is full of the guilty. You can rely on paying more if you get caught by one of these, and on being at the mercy of the manufacturer when they decide to stop sup- porting that model. You may not find out about proprietary models until it’s too late, unless you ask about compliance with industry-standard form factors, interfaces, and software standards before you buy. Be sure to ask not only about memory and disk, but also about the motherboard and power supply. You’ve been warned. If you buy a complete computer from a manufacturer, your choices in cases are likely to be whether you want a tower, mini-tower, or desktop, or want it in blue. You might have an option for auxiliary fans available. If you integrate your own machine, you’re in the market for a case and have a wide range of options. Things that make for a great case include: ✦ Gobs of room inside — We’re far more interested in a machine that’s easy to work on, reliable, and upgradable than in its being tiny. Your needs may well favor small size, but you’ll pay the price in compro- mises. Having 10 external drive bays fits our definition of upgradabil- ity, for example, but having just one does not. Chapter 21 ✦ Cases, Cooling, and Power 339 ✦ Airflow to keep the electronics very cool — We like having lots of fans. Motherboards finally have working technology to control fan speed, meaning you don’t have to choose between cooling and noise. ✦ Attention to detail — For example, you should look for heavy sheet metal that provides good support, simple case opening mechanisms that give you access to everything inside, and a lack of sharp edges that could cut you and internal cables. Cases have evolved considerably from the plain beige or black boxes you’re used to. We show you how to build a very quiet, very high performance PC in Chapter 25, but if your tastes run more to the visually extreme, the products are available to open windows to the inside of your PC, paint or carve designs into the case, and light it to show off your work. Power Supplies The power supply converts power coming into your computer from the wall outlet to the forms usable by the electronics in the system. It changes incom- ing alternating current (AC) at 120 or 240 volts to direct current (DC) at 3.3, ±5 and ±12 V. A good power supply does more than power conversion — it cleans up the spikes, surges, and sags in the utility power. Motors, copiers, appliances, and other electrical devices create noise in the power at your wall outlet, as do lightning strikes and other effects farther away. If that noise gets through the power supply into the electronics in the computer, it causes trouble ranging from erratic operation to complete shutdown. A high-quality power supply will be more resistant to these problems, giving you more reliable operation from your computer. You need to know four electrical terms to understand and compare power supplies — voltage, current, power, and frequency. ✦ Voltage is the force pushing electricity through the wire. It’s like the water pressure in your garden hose: More voltage is like more water pressure. Voltage is measured in volts (abbreviated V). In North America, common wall-outlet power is at 120 V. European power is commonly 240 V. ✦ Current is the amount of electricity flowing through the wire and is like the flow of water through a hose. Current is measured in amperes (or amps, abbreviated A). ✦ Power is the product of voltage and current (voltage times current), and is measured in watts (abbreviated W). If your computer draws 3 amps at 120 V, it uses 360 W. ✦ Frequency is the rate at which the power alternates between positive and negative voltages. Frequency is measured in Hertz (abbreviated Hz); a Hertz is one cycle per second. North American power arrives at 60 Hz; European power is mostly 50 Hz. 340 Part VII ✦ Integration Selecting good power supplies A good power supply is easy to describe but very hard to design. It must be reliable, and must deliver clean, stable power. The circuits in your computer are terribly sensitive to variations in supply voltage, so the power supply has to keep the voltage stable, filtering out the ripples in the incoming AC power and compensating for load variations from the computer circuits. Good power supplies have a wide tolerance for both fast input power variations and for ones over several seconds. By specification, ATX12V supplies must keep all voltages but the –12 V supply within 5 percent of nominal, and must keep the –12 V supply within 10 percent. Some high-quality supplies can maintain their outputs within 1 percent. You do have a choice in how much power the supply can give the com- puter. Computers with faster processors, more memory, and more drives draw more power than smaller ones. You want to leave margin for adding new hardware in the future, too, want to run the power supply at about 50 percent total load, and have to be careful not to exceed the maximum rat- ing on any individual output (including the standby power outputs). In addition to extending power supply life (by letting it run cooler), running below maximum capacity helps extend the power supply’s hold-up time during short AC power dropouts. We commonly use power supplies of about 400 W capacity for high-performance desktop computers, such as the 380 W unit we use in Chapter 25. There’s no loss in using a larger sup- ply because the computer draws only what it needs — the power supply rating is the maximum, not a constant figure. Uninterruptible power supplies The best power supply won’t help much when the AC supply goes out. Admittedly, when you’re sitting there in the dark, the work you were doing might not be your first concern, but it’s likely to be something you worry about later. Nor is a widespread power failure the only threat. We’ve seen computers taken out by plugging a vacuum cleaner or coffee pot into the same circuit. You don’t have to put up with losing your work. Once found only in major computer installations or alongside mission-critical systems, an uninterruptible power supply (UPS) is now an inexpensive addition that can easily pay for itself by saving hours of work. A UPS consists of a power supply, a battery, and a reverse power supply. Figure 21-9 shows how this works. The incoming power supply — similar to what’s in your computer — creates the DC the battery needs whenever utility AC power is available. The outgoing power supply does the same thing in reverse: It converts battery DC to AC that your computer’s power supply can use. The source of the DC power the outgoing supply receives is the incoming AC supply (if it’s operating) or the battery. Either way, the AC output is stable, with no interruption in output power as the input AC comes and goes. Chapter 21 ✦ Cases, Cooling, and Power 341 [...]... that can handle up to 2GB of memory are available PC Card and PC CardBus The exception to proprietary components in laptop computers is a standard created specifically to allow modules to plug into laptops — the PC CardBus and PC Cards This standard was formerly known as PCMCIA (Personal Computer Memory Card International Association) As is noted in Chapter 5, PC Cards support read/write and read-only... interfaces to be standard, such as use of the PCI bus, but the physical form to be smaller than the desktop version of the standard The resulting designs often don’t conform to any widespread industry standard, so production volumes and sources of supply are less and upgrades are more expensive If you’re willing to pay the price in size, weight, power consumption, and cost, however, you can get desktop- equivalent... working with and helps you connect cables to the back of the system Laptops and Handheld Computers 22 C H A P T E R ✦ ✦ ✦ ✦ In This Chapter L aptops — and now tablet PCs — are a breed apart The added constraints of minimum size and extended battery operation change the design decisions engineers make for mobile PCs, and raise the cost The convenience of using the same computer for both desktop and portable... less expensive and give you more options You’re Going to Put That Where? 23 C H A P T E R ✦ ✦ ✦ ✦ In This Chapter What follows is the chapter “Home Surveillance with Internet Remote Access” from our book PC Toys: 14 Cool Projects for Home, Office, and Entertainment (Wiley 2003) Prior editions of the PC Upgrade and Repair Bible included descriptions of interesting uses people have for PCs, but those... reduced size and weight of a laptop, tablet, or handheld device ✦ Limited battery power and the limitations of rugged, small packaging constrain how fast your mobile computer can be and how much it can store ✦ Battery technology will continue to improve ✦ You should consider both physical and communications security with mobile computing devices ✦ Upgrades using standard interfaces, such as USB and PC Card,... connections The camera interface carries audio and video to the computer, and zoom, resolution, and image adjustment commands to the camera The TrackerPod interface carries position information to the camera and pan, tilt, and LED commands to the servo base Under control of the TrackerCam software, you can point the camera, record video and stills, upload to Web sites, and monitor or control the camera remotely... surface with a stylus Windows PCs have had software support for handwritten input for many years, but it’s been clumsy and not terribly useful The failings of handwritten input drove both PDAs and tablet PCs to add keyboards The Research in Motion Blackberry PDAs have had a keyboard from the beginning; Palm PDAs added them as third-party and later first-party accessories Tablet PCs added fold-away keyboards... batteries A wide range of options in handheld computing exists with greater or lesser compatibility and interoperability with PCs: ✦ Entertainment — You can get handheld music (MP3) and video players, storing songs and movies on a compact hard drive You’ll download content from your PC or, for some units, compress directly on the player from a video source ✦ E-mail, calendar, and communications — The stereotypical... thieves may not be able to do Using the NT File System (NTFS) and passwording your Windows account keeps attackers out of the PC Chapter 22 ✦ Laptops and Handheld Computers 357 and out of the file system unless they know how to either boot from a CD-ROM and use the NTFSDOS utility, or disassemble the computer and hook the drive to another PC ✦ Use secure communications protocols — Many ISPs offer secure... stock quotes, and street maps With e-mail software, you can connect to your Internet service provider and both send and receive messages A wireless cell phone or IEEE 80 2.11b interface lets you communicate on the go, while a GPS receiver lets you navigate from stored maps Devices you plug into the PC Card slot can consume a lot of power, and there’s little to be had The batteries in handheld devices . 20.0 33.1 13.1 96.0 0.1366 B 21.9 30.7 8. 8 46 .8 0. 188 7 C 20.0 21.9 1.9 68. 4 0.0276 D 18. 6 30 .8 12.2 149.4 0. 081 8 Systems A and D consume the most power and therefore generate the most heat. The. — the PC CardBus and PC Cards. This standard was formerly known as PCMCIA (Personal Computer Memory Card International Association). As is noted in Chapter 5, PC Cards support read/write and read-only. compliance with industry-standard form factors, interfaces, and software standards before you buy. Be sure to ask not only about memory and disk, but also about the motherboard and power supply. You’ve