1. System Case

2. Introduction The metal and plastic box or outer shell that houses the main components of the computer Sometimes called the chassis or enclosure The case actually performs several important functions for your PC system.. Lets discuss some of these::

3. Aesthetics The system case is what people see when they look at your computer. For some people it's essential that their machine look good, or at least fit somewhat into their decor. In an office environment for example, PCs that all look different can give a work center a "hodge-podge" appearance that some consider unprofessional.

4. Structure The motherboard mounts into the case, and all the other internal components mount into either the motherboard or the case itself. The case must provide a solid structural framework for these components to ensure that everything fits together and works well.

5. Organization The case is key to a physical system organization that makes sense. This determines where things can be installed on the case and makes accessibility easier It also provides for ease of removal or addition if the need arises

6. Components Accessibility To remove, change or check a device in the computer, it’s important to access that device without too much difficulty. It’d be way easier not to have to remove the ribbon cables and expansion cards just to install another DIMM, or replace a battery and 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, there are 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.

7. Status Display The case contains lights that give the user information about what is going on inside the box Some of these are built into the case and others are part of the devices that are mounted into the case, we’ll discuss these shortly

8. Upgradability A user may decide to add something to their PC such as a Zip Drive, a second Hard Drive, Floppy or 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 and therefore a poorly designed case would limit expansion options If there are empty external bays, then 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.

9. Upgradability (ctd.) Any device added to the PC requires power, and the available PSU has to supply the required power. A 150 or 200-watt power supply, the system may be limited to the amount of devices that can be added. Note:: Most cases come with a power supply.

10. Protection A good case can protect the internal components from dust, vibration, foreign objects, ESD and EMI There are cheap cases that fit together so poorly 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 smoothly The stability of the case makes a big difference.

11. Protection (ctd.) Some of the case frames are left unfinished, resulting in sharp edges, burrs and metal slivers Ribbon cables and wires (and your fingers) can get cut by these sharp edges just by removing or replacing the outside cover

12. Protection (ctd.) The case protects the inside of your system from the outside world, and vice-versa. With a good case, the inside of your computer is protected from physical damage, foreign objects and electrical interference. Everything outside of your computer is protected from noise created by the components inside the box, and electrical interference as well. In particular, the PSU, due to how it works, generates a good deal of radio-frequency (RF) interference, which without a case could wreak havoc on other electronic devices nearby

13. 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. Airflow is needed to cool down the components and devices inside the case. The cooler that your computer operates, the longer it will last. Components that run cool last longer and give much less trouble to their owner. Unfortunately, cooling problems aren’t very easy to detect, one will just get random like lockups on the system. Also peripherals and drives failing long before expected Making sure the system is cooled properly is one good way to save time, trouble and money.

14. Longevity (ctd.) 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.

15. Longevity (ctd.) 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 heat sink. A spacious, well laid-out case is a critical part of proper system cooling. Small cases require components to be packed close together, which worsens cooling in two ways. First, air flow through the case is reduced because it is blocked by the components. Second, the parts are closer together so there is less space for heat to radiate away from the devices that are generating it.

16. Case Styles and Sizes Cases come in several different major styles. The two basic styles for the case are the tower case and the desktop case. The desktop is a rectangular case that is wider than it is tall and normally sits on the desk The tower is like a desktop flipped on its side and can sit on the floor or on the desk.

17. Case Styles and Sizes (ctd.) Despite the commonly-used names, there are no standards for case size or shape One company's full tower case can be very different in details from another. Some of the companies that make high-quality high-end cases incorporate very interesting features into their cases that stretch their capabilities for the same amount of space taken. As a result, one company's "mini-tower" may be able to hold more components, and cool them better, than another company's "mid-tower".

18. Case Styles and Sizes (ctd.) An assortment of different cases in the same series, showing an array of sizes and styles. From the left: a microATX "micro tower", a microATX mini tower, an ATX mid tower, an AT/ATX full tower, a microATX desktop (above), and an ATX desktop (below).

19. Mini Tower Case Popular style for new PCs the most popular of the stand-up style case It is roughly the same size as a desktop case, but due to its design is generally easier to use and often has more capacity. Also keeps components cooler than a desktop case. Since it is not nearly as large as a full tower case, many people put the mini tower on the desktop, next to the monitor. This is particularly preferable if you are using a larger monitor

20. Mid Tower Case This size seems to be all over the place; Some companies make mid tower cases that are no larger than others' mini towers. A mid tower is a good compromise for those that want more space than a mini tower offers, without going to the expense of a full tower case.

21. Full Tower Case A full tower case is the largest standard PC case available on the market. These units are big, heavy and at two to three feet in height, are intended to be installed on the floor. Most flexible, expandable cases, with many drive bays to support a large number of internal devices. They normally come with larger power supplies to support these devices (but not always) and since they are so roomy, they are the easiest to work in and the best at keeping components from overheating. This makes them the choice of many power users and homebuilders. Also the most expensive type of case.

22. Desktop System Case Was a standard for PC cases since the original IBM PC, XT and AT machines, which came in a desktop case only. Today's desktops are different than those ones were, both in size and construction, but the idea is the same: the box sits on the desk, and the monitor sits on the box. For those who don't want to (or cannot) put the case on the floor, the desktop actually saves space compared to a tower case, since the monitor won't sit on top of a tower case. A desktop doesn't, in general, let components cool as well as a similarly-sized tower, and the monitor sitting upon it can be part of the reason.

23. Desktop System Case (ctd.) A further disadvantage of the desktop case is that often, one or more of the internal drive bays is vertical. Hard disk drives can be mounted vertically Can be confusing to many users to use a 3.5" floppy disk mounted on its side, as it's hard to figure out which way the disk goes

24. Slimline Cases Also sometimes called "low profile" or even "pizza box", A smaller version of the desktop case. Invented in part as a cost-cutting measure but at least as much in order to reduce the amount of space the box takes up on the desk. For many people, this case is aesthetically pleasing because it takes up the least space on the desktop.

25. Slimline Cases (ctd.) Unfortunately, it has little capacity for additional drives, have the poorest expandability, are hard to work in, and have the worst cooling. Despite this, slimline PCs are still being sold simply because they are cheaper to build and people underestimate the performance and longevity drawbacks of tiny cases Most older slimline cases use the LPX form factor so much so that the terms "LPX" and "slimline" are sometimes used interchangeably Newer slimlines now generally use the NLX form factor, designed to replace LPX.

26. Proprietary Case Designs In addition to the standard case styles, there are some machines that use totally unique designs. Some Compaq and Apple models for example have the monitor and case in one large box. These machines are generally marketed to the home user or first-time buyer as a "home appliance" and the idea is supposed to be that this is "simpler" than having the monitor be in a separate box.

27. Proprietary Case Designs (ctd.) The main disadvantage of this design is in upgrading as follows:: To upgrade your PC you lose your monitor, and similarly, If a user decides to get a larger monitor, you have a problem because your PC is in the same box. Such integrated units are therefore inflexible and strongly recommend against

28. Proprietary Case Designs (ctd.) Special cases much larger than the standard full towers are available for servers and other high-end machines These large cases often incorporate special features such as locking front covers, slide-out drive bays and wheels (since they are heavy). They can cost as much as an entire regular PC by themselves. In addition to server-oriented full-sized cases, there are special enclosures for such things as RAID (disk) arrays available from major case manufacturers.

29. Comparison of Case Styles The table below compares and summarizes the different case styles and their advantages and disadvantages. The number of bays depends on the case, but the numbers given are typical ranges For external bays, the first number is how many 3.5" bays the case typically will have, and the second is how many 5.25" bays. Internal bays are usually 3.5“ Power supply ratings are measured in watts (W) and are just what is typical for the style. Getting a full tower case is no guarantee of a 300 watt power supply, but it's much more likely to find one in a full tower than a mini tower

30. Comparison of Case Styles (ctd.) Case StyleSizeExternal BaysInternal BaysCoolingPower SupplyCost Full TowerLarge2 + 4 or more3 to 5 or moreBest250 to 375 +High Mid TowerMed2 + 32 to 4Better200 to 300Med "Midi" Tower Small to Med 2 + 2 or 2 + 3 2 to 4Good170 to 300Low to Med Mini TowerSmall2 + 22 or 3Good170 to 250Low DesktopSmall2 + 21 or 2OK150 to 230Low SlimlineVery Small1 + 21 or 2Worse90 to 200Low

31. Case Location In choosing a style of case, there is one decision to consider: where to put it. Generally two choices: on the desk or on the floor. A tower case is generally recommended for a floor location, for stability. A desktop case can also be put on the floor, on its side, as long as it is properly secured, you don't want the box falling over If you do go with a desktop on the floor, there are brackets intended to support desktops put on their side Putting the case on the floor gets it off your desk, saving desk space.

32. Case Location (ctd.) However, major drawbacks of a case on the floor are as follows: The power and reset buttons, the indicator LEDs, and the drives, are less accessible to your fingers, and more accessible to accidents involving your feet such as kicking or knocking over the case, or hitting the power switch Need cable extenders for the keyboard, mouse or monitor, depending on the setup. Also, the size of the monitor, say 15", means it may need something to put under it so that it is at a comfortable reading level Larger monitors usually work better on the desktop directly

33. Case Location (ctd.) A desktop case is of course better for putting the machine on the desk; A tower case can be put on top of the desk but then takes twice as much room since the monitor cannot sit on top of the tower case. There are apparently some types of cases that can be "converted" from desktop to tower and back again by changing the front panel. Additional hardware may be purchased in order to make the change however One final consideration is the orientation of your drives, in particular CD-ROM drives, DVD drives, and other removable media. Many of these drives will not tolerate being mounted on their side, which means you need to consider how the system will be oriented in advance. Most modern hard drives operate just fine mounted either vertically or horizontally.

34. Parts of the System Case A system case should normally come with a number of physical components. This will vary widely from system to system, depending to some extent on the form factor and overall design of the case. If you buy a case by itself for use in building your own machine, you should be able to check for all of these items. For a pre-built system, many of these components are probably already inside the case when it was assembled The slides that follow describe the various components found with a typical, good-quality case.

35. Parts of the System Case (ctd.) Internal rear view of a mid-tower case, showing major parts.

37. Frame and Cover The physical frame of the case, and its cover, are usually made of sheet metal The cover slides off the frame when the screws that hold it to the frame are removed although some cases use no screws at all to secure the cover, Increasingly, designs use removable panels instead of an integrated cover The quality of the frame and cover is the very important and the following considerations should be made when assessing the quality of the frame and cover of the case:

38. Frame and Cover (ctd.) Rigidity: Many of the components in your PC have little tolerance for being flexed or bent; this is especially true of the motherboard A very high quality case is made of solid, heavy gauge steel (16 to 18 gauge) while slightly cheaper ones use lighter (20) gauge steel. All-steel cases have very good rigidity, feel "solid", and will keep your system from flexing. The next step down from all-steel is aluminum reinforced with steel. The cheapest cases use punched aluminum that you can literally bend with your hands.

39. Frame and Cover (ctd.) Fit: Quality cases have a good fit between their components. The cover fits securely on the frame, and any plastic panels fit without rattling or leaving large gaps. Proper fit also reduces spurious RF emissions from the PC, and helps enable the PC to be FCC certified.

40. Frame and Cover (ctd.) Finish: Good cases have their metal properly finished and trimmed, Cheaper cases often leave very sharp edges that can be hazardous to those who work within them

41. Frame and Cover (ctd.) There are so many different configurations of cases and their covers that it would be impossible to list them all. Many companies seem to pride themselves in their ability to come up with interesting new case designs with screws in the strangest of places, it seems. The following general categories seem to cover a good chunk of what is out there, however, from the earliest machines to the latest designs:

42. Frame and Cover: Conventional Desktop Describes the large cases seen with early PC/XT and AT systems, as well as many Baby AT and ATX desktops. The cover is like an upside-down letter "U", with the sides shorter than the middle (top). The cover is secured to the back of the case using usually five screws, but sometimes fewer Care must be taken when sliding the cover off the frame, not to jar any drive faceplates On some cases, the front cover slides all the way off the front of the case. On others it will slide forward a few inches and stop, and then must be lifted off the frame.

43. Frame and Cover: Conventional Tower Classic design Usually in full-sized Baby AT or ATX form factor systems. Cover is also "U-shaped", but the sides are longer than the top. There are normally three to six screws holding the cover to the back of the frame. These covers are large and can be unwieldy, and sometimes have a plastic "vanity plate" that snaps onto the back of the case to improve appearance.

44. Frame and Cover: Front-Screw Desktop An odd design found on some slimline, LPX and proprietary systems This case has the screws that hold the cover on the front of the case, and in a very hard to find spot. The screws are hidden behind small sliding plastic doors on both sides of the case, at the bottom, in front. Lifting the doors reveals small screws, which are removed to allow the cover to slide forward off the case. Sometimes there are additional screws at the back of the case as well

45. Frame and Cover: Front-Screw Tower There are some tower cases that have screws on the front of the case holding the top cover on There may be a front panel that snaps on to the front of the case, hiding the screws from sight.

46. Frame and Cover: Single-Screw Tower or Desktop Popular design amongst many brand-name PC manufacturers, (although the fully screwless design is now replacing it – see next slide) There is a single screw at the top of the back of the case, which is oversized and designed so that it can be loosened with your fingers Sometimes there are clips holding the cover to the case as well. Some of these systems have a cover that lifts straight up and off the frame instead of sliding off.

47. Frame and Cover: Screwless Tower or Desktop There are many different screwless designs No single, integrated cover; The cover comprises of several individual panels Usually the front panel pulls off first, and then the side panels slide off, followed by the top, which is often lifted straight up While these covers are a great invention, all the interlocking pieces can make it harder to access the system with a case of this type than one with a conventional cover, even if you do need a screwdriver in the latter instance

48. Frame and Cover: Flip-Top Desktop Here, a top cover simply flips up after you loosen it by pressing a button or two

49. Frame and Cover: Motherboard Tray Another innovation in case design is the removable, rotatable, or slidable motherboard panel or motherboard tray Many newer, higher-quality cases are designed to allow the part of the frame where the motherboard is mounted to be removed from the case or shifted for easier access This makes it much easier to work within the system, and can make even a small case seem much larger especially when building a PC, or replacing a motherboard in an existing system

50. Frame and Cover: Feet Attached to the bottom of the case These provide traction, especially on slippery desks. Some new cases come with their plastic feet not yet attached. Remember to install them as soon as possible when assembling the case, as it may not be possible to put them in once the motherboard and other components have been installed. Larger tower cases, especially server models, are designed to live on the floor and often come with wheels, as they can weigh in excess of 100 pounds with their components installed.

51. Front Panel and Door Most PC cases have a plastic front panel, sometimes also called a bezel, which hides the metal frame from the user and also serves to make the PC more visually pleasing. Initially, PC cases had the front panel permanently installed. Over time the marketing people decided to make them fancy and there are now available hundreds of different front panel designs Case manufacturers have responded to the desire of PC makers to differentiate their offerings, by designing modular cases with removable and interchangeable front panels. Many cases now come with a removable front panel to allow style changes. PCs are now apparently subject to the whims of fashion. For example, you will notice many new PC cases coming on the market that make use of transparent pastel colors, undoubtedly trying to ride on the coat-tails of the popular iMac in this regard!

52. Front Panel and Door Many larger cases, especially those designed for use in server machines, have gone beyond a simple front panel. These cases include one or more doors that are used for both the practical and the aesthetic. The door, which can be lockable, prevents casual access to the power switch, reset button and drives by the unauthorized. One doesn't want just anyone resetting a server, or hitting the power button by accident. It also makes the front of the case look more streamlined and professional.

53. Front Panel and Door Front view of a server case showing front panel doors. One door hides the removable hard disk drives, and the other covers everything else. The lock prevents casual access but should not be considered high security

54. System Drive Bays Drive bays are the spaces in the system case where one mounts the hard disk, floppy, CD-ROM, tape and other drives. They come in two general types, external and internal, and two sizes: 5.25" and 3.5". These bays can be 3.5 inches or 5.25 inches wide. There are internal and external bays. The external bays are seen by looking at the front of your case. Devices like floppy drives and CD-ROMs slide into external bays and can be seen (and accessed) from the front of your system case. Any unused bays should have a plastic faceplate over them. 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.

55. External Drive Bays This is a bit of a misnomer, since external means "outside" and these drive bays are certainly inside the case. However, they are called "external" because they allow access to the device from the outside. Any drive that uses removable media or has controls that must be operated manually must go in an external drive bay. Examples are floppy disk, CD-ROM, DVD, tape and removable-storage drives.

56. Internal Drive Bays These bays are entirely within the case and are not accessible from the outside. If a device does not require any access from the outside it is preferable to use an internal bay, and save the case's external bays for drives that need them. In practical terms, this means that internal drive bays are usually used for hard disk drives, which do not require any access by the user.

57. System Case Drive Bays This tower case has three 5.25" drive bays, all external. It also has three 3.5" drive bays. The top two are external; the bottom one internal. You can see that the bottom drive bay does not line up with a faceplate in the front panel

58. I/O Template or Connector Ports I/O peripherals, these include the monitor, keyboard, mouse, printer. The cables from these devices actually connect to the motherboard either by direct mounting or via internal cables from ports mounted to the case Therefore holes are provided in the case to permit access to the ports that attach to the motherboard. There are two different ways that this is done, depending primarily on the form factor of the system.

59. I/O Template or Connector Ports On older XT, AT, Baby AT and LPX cases, there are a number of discrete holes in the case itself, in the shapes necessary to accomodate the round keyboard connector, and "D-shaped" serial and parallel connectors. On XT, AT and Baby AT systems, ports were installed to these holes, with the connector facing out from the hole, and cables running from the inside of the port to the motherboard. Since some systems included more parallel ports than others, since some serial ports were 9-pin and others 25-pin, and since it was desirable to leave room for expansion, many of these older cases included more holes in the case than some motherboards required. Therefore, to keep out dirt and ensure proper air circulation in the case, most manufacturers covered unused I/O port holes. Some cases had discrete port covers that screwed in place, while other case makers just manufactured the back panel of the case with sheet metal punchouts where the ports would go, and the installer would remove the appropriate ones. On LPX systems the holes were placed to line up with one of the standard configurations of I/O ports installed directly to the LPX motherboard, instead of mounting ports to the case itself.

60. I/O Template or Connector Ports Newer form factors, including ATX (and its variants), NLX, and WTX, specify that the I/O ports be mounted directly onto the motherboard in either a single or double row. A wide variety of configurations is possible, to provide motherboard manufacturers the flexibility to design solutions for various PC requirements. To accommodate this flexibility, cases designed for these form factors did away with the rigidly-placed I/O port holes in favor of interchangeable plates with different configurations and patterns of holes. These removable metal plates are called I/O templates, or sometimes I/O shields. Often, a case will come with templates that correspond to one or more of the most popular motherboard designs used with that case, but these may not match up well with every motherboard.

61. I/O Template or Connector Ports Close up of I/O port holes (one keyboard, two 9-pin serial, and two 25-pin serial/parallel) on the back of a typical Baby AT form factor tower case. Note that the sheet metal "punchouts" are still in place in the serial and parallel port holes. The black keyboard connector on the motherboard is visible through the case's keyboard hole. A set of ATX I/O templates showing hole patterns corresponding to different motherboard I/O port configurations. From left, a single-row I/O port template; a double-row template; and a template with just a keyboard connector hole. The last template could be used to allow installation of an AT form factor motherboard in a combo AT/ATX case. Serial and parallel port holes would of course need to be elsewhere on the back of the case for the AT motherboard.

62. Power Supply The power supply often comes with the case, even though it isn't really part of the case. PSUs come with an integrated fan, secured to the back of the case in AT form factor supplies, or the front for most ATX PSUs. The power switch for AT and earlier form factor cases is really part of the power supply; for ATX, NLX and WTX form factor cases it is a separate component attached to the case. The switch on most modern PCs is mounted just behind a plastic button that is accessible from the exterior of the case. Most cases also come with a standard power cord, usually black, to plug the power supply into the wall. Not all cases come with a power supply. Don't assume that a more expensive case will have a power supply included and a cheaper one won't. (Those who care about getting a good power supply, an important but oft-ignored component, often prefer to purchase it separately.)

63. Power Supply A microATX/SFX power supply

64. LEDs, Speaker and Connecting Wires A standard PC speaker is usually mounted somewhere inside the case, but may be loose in a new case. There are special wires for all the LEDs and for the speaker, to be connected to the motherboard or drives.

65. Mounting Hardware It’s important to have the appropriate mounting hardware or your system assembly will stall in pretty short order! A new case should come with mounting hardware. These pieces normally come with the case, not the motherboard. Some cases actually come with their mounting hardware fixed into position and not movable. Theoretically, this is a time saver, but it may reduce flexibility to upgrade. The exact hardware included varies greatly and depends on manufacturer decisions, but will generally find some combination of the following:

66. Mounting Hardware: Plastic Standoffs Also called "spacers", "sliders", these are generally made of white plastic and are used for mounting the motherboard to system cases that have large eyelet holes. They have a collapsible point on one end and a round disk on the other. They were originally created to make motherboard installation "easier" since they do not require screws A plastic standoff (or spacer), commonly used to mount motherboards to cases that use standard mounting holes

67. Mounting Hardware: Metal Standoffs Again also called "spacers“, these are 3/16" hexagonal nuts with a threaded screw on the end. They are usually made of brass, sometimes steel, and they are used for mounting to threaded holes in the system case. Other cases have done away with standoffs in favor of metal "dimples" that stick up from the case to support the motherboard.

68. Mounting Hardware: Screws These are used to screw the motherboard to the brass standoffs mentioned above.

69. Mounting Hardware: Washers Generally made of plastic or paper, these go under the screws to keep the screw head away from the circuitry on the top surface of the motherboard. Now being omitted in new system cases because they are less necessary now than they once were because nowadays motherboards tend to keep the circuitry farther away from the screwholes than they once did

70. Faceplates Sometimes called bezels Provided for drive bays that are not in use. Some cases come with these pre-installed but it’s important to keep all open bays covered, to keep foreign materials out of the computer. Tower case with three 5.25" bezels and two 3.5" bezels in place. At rear, seven expansion slots have their inserts installed

71. Expansion Slot Inserts Metal expansion slot inserts to cover the space used by slots that don't have cards in them. Once punched out they can't be put it back in so if there are any changes a card's slot, inserts that screw into place are needed to cover the hole. Some of the cases with stamped metal slot covers also come with real ones you can screw in place later if you need them Leaving expansion slots open adversely affects air flow in the case, and thus cooling, and also increases the chances of system contamination.

72. Keylock Keys Some system cases have a keylock used to lock out the keyboard. The system case should come with keys for this keylock; make sure you keep them in a safe place. Cases with locking front panel door(s) also will come with keys to lock the front of the case. There are usually two of each type of key. People tend to keep them together so that they can lose both at the same time

73. Case Switches Most cases have either two or three switches on the outside of the box, and they are usually the same. Case switches are used to control the operation of the PC at its most basic level. Some cases also have a keylock that you can use to prevent operation of the computer.

74. Case Switches Power, turbo and reset switches (with LEDs) on the front of a tower case.

75. Power On/Off Switch The power on/off switch for modern PCs is on the front of the case. Older PCs, using the PC/XT or AT desktop form factors, have no power switch on the case at all; the case is designed so that the on/off switch of the power supply is accessible directly through a hole in the case, usually at the rear. On most Baby AT form factor cases, the power button doesn't in fact do anything other than mechanically transfer the "push" of your finger to the real metal or plastic power supply switch that is behind it. The remote switch is in fact part of the power supply, and so is discussed in when we talk abt the PSU. Newer form factors, including the ATX family, NLX and WTX, have a true power switch on the case, which is connected to the motherboard. The motherboards on these systems turn on and off the PC, not the power supply directly.

76. Reset Button The reset button is a simple normally-open switch that is connected to two pins on the motherboard. When the button is pressed, the switch is closed. When it is released, the system performs a hardware reset. Most newer cases have the reset switch recessed to prevent it from being pressed by accident (or by small, curious fingers.) Some put the reset switch on the back of the system, which is even safer, but can also be very inconvenient. Strangely, there are some cases on the market that do not have a reset switch at all. This sort of design would also increase the chances of accidental system corruption: since the only alternative to the reset button when a PC is hung up is to turn the PC off and then on again, which can occasionally cause system problems.

77. Turbo Button A leftover from old machines of five to ten years ago, the turbo switch still remains on many cases, even though it really serves no purpose any more. In the early days of the PC, there was only IBM, and there were only a handful of different speeds a PC could run at. Early software was written by programmers who believed they were writing it to run on a machine of a specific speed. When newer, faster machines would come out, some of this software (especially games) would stop working properly because it would run too fast. Turning off the "turbo" function of the PC (which meant anything that made it run faster than an IBM of a particular era) would make the machine run slower so this software would work. In essence, it was a "compatibility mode" feature, to slow down the machine for older software. Now, there are dozens of different combinations of processor types and speeds. Software cannot rely on knowing what the speed of the machine is, so most programs use speed-detection algorithms to determine how fast the machine is. The turbo button no longer serves any useful purpose, and in fact on many motherboards there either isn't anywhere to connect it, or there is a place but the motherboard does nothing when you press the button. The best use for this button is to never touch it, or use it for some other purpose. Some older machines will still slow down when the button is pressed, and if you press it by accident your machine will lose performance; it can be surprisingly hard to track down the problem, since it seems that the front of the machine is the last place anyone appears to notice anything. :^) You can correct this problem if you find yourself doing this frequently.correct this problem Fortunately, the turbo button has all but disappeared from modern system cases, especially newer NLX, ATX-family, and WTX form factor systems.

78. Keylock Some cases have keylocks, which when locked, essentially lock out the keyboard. The system detects this condition and puts an error message on the screen, effectively disabling access to the computer. This can be useful in an office setting to prevent casual access to a computer that is normally kept off. It can also effectively prevent your kids (or parents! :^) ) from booting your PC when you are not around. The keylock should be considered a minimal security device. The keylock prevents the system from booting, but this doesn't prevent someone from opening up the box and disabling it. I can get around a keylock with three minutes and a screwdriver--but I can't do that when people are around, as it would be very noticeable. This gives you a good idea of how much to trust this device. If you really need security for your PC, there are numerous hardware and software products on the market that can be used to give you some peace of mind (although a locked office is probably best and simplest in many cases). See this section in the Optimization Guide for more ideas.this section in the Optimization Guide

79. Keylock The keylock from one of my PCs, an old Gateway 486 tower model that has been upgraded so many times that all that's left of the original is the case and power supply

80. Keylock The main problem with keylocks, of course, is that if you lose the keys you will have to get new ones somehow or get a technician to disable the keylock switch from the inside. To make matters worse, many cases that come with keylocks are interchangeable--the companies aren't bothering making different locks. So if you have an office and buy 10 of the same type of PC or case, any key may unlock any PC, depending on the model. I personally don't use keylocks on individual PCs and usually recommend that people just take the keys, put them somewhere safe--and forget about them. The only major exception to this general suggestion would be for a server in an area where many people have physical access to the machine; the keylock will at least prevent casual tampering (though a locked door is still a better idea.)

81. System Case LEDs "LED" stands for light-emitting diode, a low- power component that emits light when supplied with electricity. Most cases have at least two LEDs, to indicate power and hard disk activity. Some have several more LEDs to indicate turbo status or other functions (though "turbo" is now outdated and not generally seen on new PCs.) Most cases have the following LEDs on the front panel, which vary greatly in style, shape and color but usually work the same way.

82. System Case LEDs LEDs on the front of a typical tower case; this model has them along the very top edge of the case, but they can appear anywhere the designers choose. These LEDs use the classic colors of green for power, red for hard disk activity, and yellow for turbo. All three LEDs are lit (the power LED tends to get "washed out" by the lighting used for these pictures.)

83. Power LED The power LED is usually green and pretty simple: it comes on when the power is on. The wires from this LED are often combined with the keylock wires

84. HDD Activity LED The most important indicator on the case, this LED normally flickers on when the hard disk is being accessed. It is important in that it gives you a visual indication of how active your system is, and can help ensure that you don't shut off your system while the hard disk is active (which you should never do). Originally, when PCs had only one hard disk, this LED was connected directly to the hard disk. Newer systems have this LED connected to the motherboard, or the disk controller card (if the motherboard does not have integrated disk controllers, or if an add-in hard disk interface card is being used). This is preferred because if you have more than one hard disk, the system can activate the light whenever any of them are accessed. Larger cases, especially those designed for use as server PCs, will often have multiple hard disk activity LEDs, to allow separate connection of a number of drives.

85. Turbo LED The turbo LED is often yellow in color. It will obviously only mean something if your system has a turbo button that is connected and working.turbo button Many systems have this LED set permanently on regardless of the position of the turbo switch. If the turbo switch is functional on the PC, the LED should reflect its status (on or off). Many newer cases skip the turbo LED entirely, and you won't find it on newer retail PCs.

86. Speed Indicator LEDs Some older PCs have a digital LED readout that shows the "speed" of the processor, usually comprised of several LEDs that taken together can form different combinations of numbers, like a digital wristwatch. These are obsolete today but they were quite popular for many years, especially in systems that used the turbo button--the speed indicator would change the system "speed" when the turbo button was changed. Why do I keep putting the word "speed" in quotes? Well, these speed indicators don't really measure anything. They are not connected to the processor or the motherboard at all. These indicators are programmed in hardware (using jumpers inside the case that you can change) to show whatever value the person who assembled the case wanted them to say. There are usually two different values that can be displayed, one when the turbo button is pressed in and one when it is out. A reputable system vendor will make sure these values match those of the real processor inside the box. And a disreputable one? Well... Also, if you upgrade your processor to a faster model, these numbers will remain the same unless you change them yourself.