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Inside the Computer's Case

 

Overview:
Keep in mind that this is one of the most basic computers. It has all of the necessary components needed for basic operation (many integrated into the motherboard) but it isn't anything special. Other computers will have many more components inside of them.

Overall Side View:
The following image shows the side of the computer with the left side cover removed. As you can see, it's mostly empty space. If you look at the top left (with the white sticker on it), that's the power supply. All of those yellow, red, black and orange wires originate in the power supply. It converts the household mains voltage (120 volts AC in the US) to ±12v, ±5v, and +3.3v (all DC voltages). Virtually all power supplies have fans. This is many times the source of the noise you hear when the computer is on. I will go into more detail on variations in power supplies on a page later in the tutorial.


Expansion Slots:
As I said before, many components are integrated into this motherboard. Some of the components that are integrated are the LAN card, the video card and the sound card. Many times, those components are not part of the motherboard. If those components were not included with the motherboard, we would have to have some place in which to connect the LAN, video and sound cards. This is accomplished by using the brown, green and white slots on the MB. The green slot is an AGP slot. It's used exclusively for video cards. For the LAN and Sound cards, we would have 2 options on this MB. The brown, CNR (Communications Network Riser) slot can be used for 'low end' sound cards and LAN cards (also known as NICs - Network Interface Cards). For high end sound cards and LAN cards, we could use the PCI slots (white). If you look at the back (left) side of the computer case, you can see a series of metal slots (covered at this time). If you were to use one of these slots, you would remove the corresponding panel from the rear of the computer and install the card. The cards are fixed to the case of the computer with one screw (you can see the holes adjacent to each cover).


The Hard Drive:
I've heard many people call the computer (the entire case that holds all of the components), the 'hard drive'. In reality, the hard drive is just this little device that you see below. We showed you the insides of an older hard drive earlier in the tutorial. This is a 40GB (forty gigabyte) hard drive which makes it one of the smallest (in capacity) available. In a few years, I doubt that anyone will be making 40G drives. Even though this drive has very little capacity, it is no smaller, physically, than a 300GB drive. Larger drives simply have more capacity per platter and maybe more platters (I'm not sure if this drive has more than one platter - I doubt that it does). If you look at the back of the drive (to the left), you can see the wide, gray IDE cable. A little closer to the camera, you can see a series of copper/gold pins. These pins are jumpered to configure the drive. You set the jumpers to make the drive act as the master drive, as the slave drive (you need two hard drives to use it like that) or to allow the cable connection to determine whether it's the master or the slave.


Memory:
In the next image you can see the memory (in the yellow slot). For the most part, all memory sticks essentially look the same. Some may have larger chips or the number of chips may vary slightly but there is little other physical difference for the type of memory used. This is a stick of 256MB (megabyte) DDR (double data rate) RAM. If it were a stick of 512MB RAM, it would essentially look the same (if it were DDR RAM). If you have the wrong type, it won't fit into the slot (except for some older memory in older systems). This is due to the 'key' that's molded into the memory slot. If the key doesn't match up with the notch in the memory stick, it will not be able to be seated in the slot. The most common memory is 184 pin unbuffered memory without error checking. That's what's in this computer.


PWM Regulator:
As was mentioned earlier, the power supply produces the voltages needed by the computer. Well, there is another voltage conversion needed. It's for the CPU. The CPU runs on very low voltage. This particular one runs on 1.65 volts. Some run on 1.4 volts. The lower voltage allows more efficiency (less energy turned to heat) at the high operating frequency used in the CPU. To get from the 3.3 volt to 1.65 volts, the computer uses a switching voltage regulator. In the following picture, you can see 4 black squares (3 legs each) soldered onto some silver areas of the circuit board. Those are transistors. The transistors in conjunction with two of the coils (wrapped on green cores) and a few filter capacitors regulate the voltage down to 1.65 volts.


Heatsink and Fan:
I couldn't get a good picture of the heatsink and fan so I took the following picture of a similar heatsink and fan (HSF for short). As you can see it's simply a fan mounted to the heatsink. The heatsink is then mounted so that it makes contact with the core of the CPU. The heatsink soaks up heat from the CPU. If there were no heatsink, the processor would fail (if there were no thermal protection built in - thermal protection is getting more common). You probably noticed the copper plate on the bottom of the HS. Since copper is a better thermal conductor than aluminum, the copper plate is used to make the heatsink more efficient. An all copper heatsink would work a little better but would cost a lot more. Although you can't see it, there is a 'thermal paste' between the copper and the aluminum. This is needed to make the thermal transfer more efficient. The thermal paste fills tiny voids between the two pieces of metal (where there would otherwise be only air).

In the image above, you will notice that the fan has 3 wires. It only needs two to operate. The 3rd wire is the 'tach' (tachometer) wire. It allows the motherboard to monitor the rotational speed of the fan. If the option is available, the motherboard can sound an alarm if it sees that the fan has stopped. It may even be able to shut the computer down to prevent damage 'before' the CPU overheats. I don't know if I mentioned it before but there are color codes for the power supply and wiring but fans are different.

Power Supply Wiring Color Codes:

  • Red: +5v
  • Yellow: +12v
  • Orange: +3.3v
  • Black: Ground

Fan Wiring Color Codes:

  • Red: +12v
  • Yellow or Blue: Tach
  • Black: Ground


Power Supply:
The following images are of a generic power supply. It is rated to produce 350 watts. If you look at the label, you can see the various maximum current ratings for the various output voltages. This is a mid-line supply. Some are rated at 600+ watts. Others as low as 180 watts. A minimal computer similar to what I'm using in the tutorial won't need anything larger than a 250 watt supply but it's always good to have more power than you need. A supply rated to produce significantly more power than you need will run cooler and live longer than one that's continually being pushed to its limits.

Power Supply Plugs:
In the next image, you can see the various power supply plugs. The following is a list of their function:

  • 4-pin Molex: Used for hard drives and optical drives (CD/DVD drives)
  • Small 4-pin (in-line pins): Floppy drive or card reader
  • Square 4-pin: Auxiliary 12v output for high-end processors that draw lots of power
  • 20-pin: Main power supply to motherboard
  • 6-pin: Auxiliary power - typically for older boards

 
 
 
 
 
 
 

The following computer is a little more complex than the one above but they both serve the same purpose.

 

 
 
 
 
 
 

If you have any suggestions for this page or for the computer pages in general, please Email me.
If you're interested in electronics or car audio, you may be interested in my car audio site. It has lots of graphics and covers virtually everything associated with car audio.
If you're interested in macro photography basics or want to see lots of close-ups of insects and spiders, you may be interested in my macro-photography site.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Perry Babin 2005
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