Physical Components of Computer Systems
Desktop System Boards
System board form factors
- Yes, I prefer to call them system boards rather than motherboards. If the boards had little baby boards that nursed off of them for awhile, then grew bigger and bigger, and eventually become motherboards, or fatherboards, themselves, I would call them motherboards. But they don't. The only boards that might possibly be considered to be "sucklings" upon a "motherboard," are usually, and inconsistently with the analogy, called expansion boards (a daughterboard is something else altogether), rather than "suckling boards," "offspring boards" or "child boards." These expansion boards suckle forever; and each expansion board remains plugged in at the same spot, called an expansion slot as opposed to being called a "nipple," until a technician, or a curious human child investigating its parent's computer, pulls it away. The expansion boards are never weaned; they never "grow up." So to me, system board or main system board seems more appropriate than "motherboard," for what the expansion boards plug into.
- Here is a link to detailed information about the ATX form factor. For the test, you ought to be able to distinguish between an ATX board and an AT board.
- The Power Supply.
- The ATX power supply, which is used with an ATX board, or related system board,
does not have an On-Off cable connecting it to an On-Off switch, as the older AT power supplies did. Instead of being managed through the power supply, computer on-off is managed through a cable from the system board to the on-off switch. The on-off cable comes from the same jack on the sytem board
that supplies power to the power LED, the reset button, and the hard drive LED.
- The maximum amount of power capable of being supplied (output) by the power supply, described in watts, or as wattage, is what you need to know when choosing a power supply. At any time, the wattage supplied by the power supply is less than the wattage consumed by the power supply. How much less is a function of the efficiency of the power supply. You need to determine whether the power supply will supply enough power for all the things you are going to connect to it. Power supply units usually described by their output wattage. This nominal wattage is the maximum wattage they are capable of supplying, as opposed to a wattage level at which they are alway running. The actual power that is supplied is a function of the number and kinds of things attached to the power supply; the maximum power that a power supply is capable of supplying, is a function of the power supply itself.
- The documentation for items that use a large amount of power, such as video cards, will generally have recommendations as to how large, in terms of (maximum possible) watts, a power supply you should have. Items such as disk drives will include information in their specification sheets, about how much power they consume. Theoretically, you need to add up all the watts, then pick a power supply that supplies that many watts, and then some. However choosing the right power supply may require some guesswork, as not all manufacturers of all items publish each item's power requirements. On the A+ tests, you won't be asked about too much detail. Just know that the power supply should supply the sum of the wattage requirements of everything plugged into it, plus a bit more for margin of safety. In real life: good luck picking a power supply.
- For the tests you'll need to know the several output voltages provided by ATX power supplies. This info is easy to find on the net. Lots of information about voltages and wattages are also listed on a label on each unit. All ATX power supplies generally have the same voltage outputs. The input voltage requirement must match the voltage that is supplied by the wall socket you are going to plug it into. This is 120 volts in the United States (and 60 cycles per second). Most power supplies have switchable input voltages. You should make sure you set the switch correctly before plugging it into an outlet.
- Unfortunately, you won't be asked about how wattage, voltage, and amperage are related mathematically. But you should know this. Look it up. Ohm's Law.
- You won't be asked about the different systems, built into a power supply's design, for adjusting the power supply's voltage, or about power level regulation, or about systems for voltage, current, or power protection — systems such as active Power Factor Correction (PFC) or Passive Power Factor Correction. But these are nice to know about when actually choosing a power supply. Power supplies that put out more voltage or current than they are supposed to, can damage what you have connected to them. People often are overly cheap when purchasing power supplies, buying one that has the highest (maximum) wattage rating for the money, thinking that if it stops working, then can always buy a cheap new one. For 2 units that provide the same power, a high-quality unit may cost more than twice as much as a cheap one. But what they may not realize is that if a power supply doesn't function correctly, it isn't necessarily just a matter of your needing to just buy a new power supply. This is usually the case with computer components; if something goes wrong with one component, it doesn't damage other components; but it isn't the case with power supplies. Depending upon what goes wrong with it, it can damage things powered by it, and so you may also have to buy new ones of those, too. That is the reason you should learn about voltage, current, and power protection, and why perhaps you should not skimp on a power supply.
- You may want to take power supply quietness, and efficiency, into consideration, too, when buying a power supply. Not likely to be on the test.
- Power supply manufacturers will tell you about fan size, or fan placement, and suggest that their configuration supplies better cooling than some other configuration. I don't think you really need to know too much about this when buying a power supply. As long as the fan provides for adequate cooling, you're ok. Perhaps you might want to be concerned about whether the power supply fan has ball or roller bearings, as opposed to sleeve bearing. I could be mistaken, but I tend to think probably your power supply transformer or electronics will fail, before the cheapest fan fails. Keeping the fan clean will help it last. Suck dust out with a small, non-static-producing, vacuum cleaner. Blowing dirt into the power supply is not a good idea. After most of the dust is is vacuumed out, you might want to blow away any dust that has accumulated around the fan bearings. Clogged bearings will slow down the fan, and cause the power supply to overheat, and fail, as well as cause the fan itself to overheat and fail.
- The System Board
- Open the case, look down on the system board,
and identify the front and the rear. However note that with a tower case, you
would need to lay the case flat to see the board this same way, when looking down on it.
- The rear is where any ports that are in expansion slots, would be accessible, and where the power cord plugs into the power supply, and where air from the power supply fan is exhausted.
- Now, for an AT case, the rear of
board is one of the short sides of the rectangular board. Memory and expansion slots are both
parallel with the board, lengthwise. The CPU is at front. Expansion cards are at
the left, memory cards at the right. Disk drive jacks at left front, power supply jacks
(usually 2) at right rear. Rear connectors require cables to the rear of
case, from jacks in system board. Power supply (at rear) is far from
- For an ATX case, rear of
board is at one of the long sides and expansion slots are parallel to
the width. Memory slots are parallel to the length of board, and are across the front.
CPU is at right, to the rear of the memory. Power supply jack right front
or mid-front. Disk drive jacks generally to the left of it. N bridge
and S bridge are both to the Left of the cpu. Rear connectors are soldered
directly to system board. Power supply (at right rear) is near cpu.
- On a tower, the length
of the board would extend from the bottom to the top of the tower; and on an ATX board, the cpu would be at the top.
The rear of the board would be at the left, and memory at the right. In other words, look at the front of the tower, tilt the tower case to the right and, and, in regards to the system board, you would have the configuration of a desktop case.
- Micro ATX is like ATX, but smaller.
- NLX: with this form factor, all expansion
cards plug into a riser. NLX is New LPX. LPX is a Low Profile board.
- There are a few other form factors you should know exist. BTX for example.
- And you should know that sometimes video is integrated onto the system board; sometimes it isn't and you need a separate card. Know the advantages and disadvantages of either. These should be fairly obvious. Sound is almost always integrated these day. But you can buy a separate sound card and use the computer setup utility to turn off the on-board sound or onboard video. Although you may be able to configure these from something you can select in the Control Panel instead, or in addition. Same goes for network interface.
System Board Configuration; Setup Utility
- CMOS, called PRAM
in Apple (Parameter RAM). Officially called computer setup or computer setup utlities. Press the correct key at the correct time during boot up, to take a look at this. To find the correct key, read the help files that come with your computer or system board, or read the documentation that you may be able to find at the web site of the manufacturer of the system board, or of the BIOS.
- Or, worse comes to worse, you could try holding down a bunch of keys at startup to generate a keyboard failure error. Then you may be prompted to "press F1 to enter CMOS setup." For some system boards this works, for others it doesn't.
- Nonvolatile RAM.
Both CMOS and flash memory are non-volatile. CMOS requires battery to
stay alive. EPROM – uses ultraviolet to erase, EEPROM uses electricity
to erase. Neither require a battery to keep their memory alive. CMOS was often used for computer Setup Utility. Easier to write to than
an eprom or eeprom.
- Portion of BIOS
where PnP info (plug and play) is stored is called Extended System Configuration
Data Area. ESCD area.
- The user password configured in the "CMOS", in the setup utility, prevents people from using the computer unless they know the password.
The supervisor password prevents them from accessing the setup utility.
- CPU socket, slot.
Pentium 4 uses socket called "478." Earlier boards may use a 423 socket. Pentium M, Celeron M socket
479. Xeon, socket 603. P4 or Pentium D dual-core, Socket T (LGA 775).
Pentium Pro socket 8. Pentium 2, 3, Celeron, slot 1. Pentium 2 Xeon,
3Xeon, Slot 2. SEC stands for “single edge connector” which puts
the processor on a circuit card that goes into a system board slot similar to the way an expansion card goes into a pci slot. This is instead of plugging the processor into a PGA (pin grid array), like is done with later processors. PGA (with
ZIF). PGA478 is being replaced by LGA775 Land Grid Array). Also called
socket T. My new P4, the HP DX2200, has an LGA 775. My older P4 computer,
The Compaq Evo, has PGA 478. My new gigabyte P45 board has LGA775. There
are also the 370, 423, and 478, which look similar. 478 has that many pins. 370
first used for P3. 478 for P4. These are mostly for Intel. AMD uses,
for example, 754, or 771.
- Internal cache,
external cache. In processor or system board. Also called level 1 and
level 2 respectively.
- In addition to CPU, the system
board has a chipset. Subset of chipset are northbridge
memory, video, highspeed video slots. Manages communication between
southbridge chipset and rest of computer Video circurity if onboard,
will be built in to northside chipset.
peripherals, ps2, parallel port, IDE, LAN audio, Firewire, usb, pci.
is supported by Pentium4 2.8 ghz processor but not Pentium4 2.4 ghz
- Your “chipset
drivers” are not really drivers. The “chipset software installation
utility” is an inf file. This is a text file with configuration data about the chipset.
- PCI bus is
132 MBps for 32 bit bus and 264 MBps for 64 bit bus. Compare to usb which
is only 60 mBps. Ultra ATA is the same as ATA/33, used for EIDE (PATA)
disk drives, has speed of 33 mBps. At this point an 80-wire cable is
needed. Connector is still 40 pin. They go up even further, to 133 mBps.
Ultra ATA/133. ATA-7. Transfer mode UDMA6 (as opposed to PIO)
- PCI connector is
124 pins. 4 interrupt lines. Not the same as IRQ hardware interrupts.
- Bus mastering
is the capability of devices on the PCI bus (other than the system chipset,
of course) to take control of the bus and perform transfers directly.
The PCI bus is the first bus to popularize bus mastering; probably in
part because for the first time there are operating systems and software
that are really capable of taking advantage of it.
- To have bus mastering
you must have a PCI bus (PCI bus would have PCI slots) which supports
it, and a PCI card which does bus mastering.
- Bus mastering is
supported, generally, by the pci slot closest to the keyboard connector.
But there may be more than one pci slot that supports bus mastering.
- PCI-X is different
than PCI-express (PCIe). Former is not often used anymore. Have “lanes”
of bandwidth which gives them numbers such as PCIe-16 which has 16 lanes.
Each lane is a Low Voltage Differential Signal pair of data lines. 5.5GBps.
Full duplex. For more info on PCI see this page.
- You can plug cards
with fewer lanes into slot with more lanes, but not vice-versa.
- AGP is modified
PCI. Not as good as PCIe.
- Some boards have
Audio Modem Risers.
- POST card can be
used for diagnosis. Plug into slot.
System Board Memory
- A memory bus is a "data
line" between the CPU and the system RAM. A memory bus can be 32 bit 64 bit. More like a road a bus travels on, than an actual bus. The actual vehicle for carrying the data, is electricity. Perhaps you should just note that you can have a CPU with 32 bit internal
registers and a 64 bit memory bus.
- Frontside bus is
for main memory. Backside bus for L2 cache. Northbridge chipset. Remember: Northbridge,
frontside. Southbridge, backside.