a simple essay


Behind a Motherboard

This month’s article is a continuation of my computer fundamentals series. This month I will continue with the Motherboard.

What is it? A motherboard

If you ever open up that black box sitting next to you, the first thing you will notice (besides all the wires and dust) is a green or yellow colored electronic board with all sorts of things sticking out of it and plugged into it. This is the motherboard, and it’s very intimidating. Some of the things that you will often find plugged to this board are cables, other smaller electronic boards, and a big fan on top of a heat sink (a brick looking object made of metal blades used to dissipate heat) which hides the CPU (they get very hot). If it takes up a lot of space in the box, it must do something important right? What does this board do?

The motherboard, or sometimes called the mainboard, of a computer is very much like the human body. It is made up of several different systems which interact and coordinate with one another so as to prevent the computer from freezing up every hour. This is a daunting task. The human body alone has several systems, including the central nervous system, the respiratory system, the cardiac system, and digestive system, which all have different functions and parts! Just looking at this list of components in the human body can give you an idea of how complex a motherboard can be. The motherboard is the nervous system that allows all the different components in a computer to work together. Because motherboards are so standardized, it is unlikely that you will care what type is in a computer you are thinking of buying.

What kind of systems can we see in a motherboard? Most of the important components go straight onto the motherboard: the CPU, RAM, Video, Hard Drives, and input devices like keyboards and mice. There are other components that can be connected to the motherboard, but for simplicity’s sake, I will leave those until later. The reason I have noted these important parts is because of the general computer model proposed by the famous computer scientist Von Neumann, who laid down the guidelines for most computational devices we see today. This guideline describes the general computer with 5 components: a computational unit, a control unit, a memory unit, and input and output units. All modern PCs boil down to these basics: the CPU does all the processing, computational, and control work; RAM and Hard Drives are the memory units that store information for short or long term use, and Monitors with keyboards and mice are the inputs and outputs of the system which let a user see and input data. From this perspective, the motherboard is responsible for getting information and data to and from all four parts.

How it works:

It is helpful to keep in mind that all communication that happens in a computer is no more than electrical signals, and that these signals only do any significant work because of the clever arrangement of circuits. So, while realistically a motherboard is just the electronic highways for the electronic currents to get from a component to another component. However, this does not do the motherboard and its parts justice. It is a very complex task to move signals in the right order, and in the right manner, to the right recipient. Also, to complete the job of connecting all these components together, the motherboard includes two special processors that work on controlling the communication of data to and from all the devices in the computer. These chips are called the northbridge (which can communicate with the CPU, RAM and usually Video) and the southbridge (which communicates with all other devices) because of their position on the motherboard (the northbridge is closer to the boards “top” while the south bridge is closer to the “bottom”). Although, not all motherboards work this way; some put the functionality of both chips into one.

These two processors work very much like two middlemen. Since every computer part has a specific way of communicating with the outside world, or what is commonly known as an interface, then these two chips need to know all these different interfaces. In essence, they have to translate one type of request from one component into something the prospective part will understand. To illustrate how this works, remember that processors are always asking for more instructions with which to work. All these requests for information are sent to the northbridge through the FSB, the channel that connects the two chips. The northbridge must now change the request from the processor to a request for memory. It has to do this sort of translation because of the different interfaces and channels by which the processor and memory use. A Pentium 4, for example, can send a request to the northbridge for some specific memory while the northbridge has to be more specific when it relays this request to RAM, specifying which chip, row, and column in the memory is needed (do not worry if you are unaware of what a column and row are when referring to RAM, just know that the northbridge has to be a little more specific).

Technologies: The Northbridge

Since the northbridge is the CPU’s connection to the rest of the computer, all devices which the CPU uses often (like memory), or which require quick access to memory or the CPU are the responsibility of the northbridge. As such, you will usually find the interfaces for the CPU, Memory, and video in the northbridge, though new computers have been adding more interfaces in this chip such as Gigabit Networking. I have already spoken a little about the interface of the northbridge to the CPU, the Front Side Bus, in my previous article, so I will only focus on memory and video below.

One of the newer developments in northbridge technology, specifically in RAM interfaces, is dual-channel memory. The difference between dual-channel and the traditional single-channel memory is the addition of an extra memory interface or channel. Typically, one interface can access up to 4 memory modules at a certain speed. Adding a second interface and as such another channel, allows for faster access to memory. Think of these channels as water canals flowing into a lake; two canals flowing into a lake will fill it quicker then a single canal.

3D games and video cards require fast access to the memory and CPU, and they are the reason why there is a dedicated video interface, the Accelerated Graphics Port (AGP), which is located in the northbridge. This does not mean that this is the only place to add a video card to a computer; video cards traditionally used the PCI interface that is found in the southbridge. Cheaper computers sometimes include the video processor in the northbridge. These included processors, called integrated video solutions, are not very complex and are barely capable of 3D graphics. Although the current standard for video is the AGP interface, within the next year a new interface based on PCI express will be replacing AGP. This new interface, PCI express for graphics or PCI express x16, will not provide any significant performance increases for the moment and is being brought out as a future-proof replacement.

Technologies: The Southbridge

Besides the interfaces for the hard drive, the southbridge also has general interfaces for “add-on” cards and may sometimes include the functionality of some add-ons. For example, just like sometimes computers will advertise integrated video, they might also advertise integrated audio that is found in the southbridge. Some technologies that have been associated with this chip include: PCI, ISA, USB and ATA. These technologies can be divided into motherboard connections, external connections, and hard drive connections.

PCI and ISA along with the new PCI-express (which is a little rare at the moment) are standards for “add-on” cards such as sound cards and networking cards which are plugged onto the motherboard. It is very much like adding to the capabilities of the system. There are many different types of “add-on” cards that you can find, from radio and TV tuners so you can hear the radio or watch TV, to expansion cards that will add extra hard drive or USB connections. PCI is the current standard which replaced ISA several years ago. PCI express is a new standard that was introduced this year and is meant to replace the popular, yet limited PCI.

External connections like USB or FireWire allow printers, scanners, cameras, camcorders and other input devices to hook up to a computer. There are currently two versions of USB which run at different speeds. USB 1.1, which was introduced in the mid 90’s, has a max speed of 12 Mbps. Keyboards and mice usually use USB 1.1 since they do not require a high speed access to the computer. Devices like digital camcorders, scanners, or memory sticks do require high speeds, and as such they typically use USB 2 or FireWire connections which have speeds up to 480 Mbps and 400 Mbps respectively.

Hard drives in current computers can connect through two interfaces, the new Serial ATA, and the previous ATA or Parallel ATA. Like the current phase out of the PCI interface, Serial ATA is meant to replace the now limiting Parallel ATA standard. Although the current defining feature between the two standards is speed (max speed of Parallel ATA is 133 Mbps, while Serial ATA has current speeds of 150 Mbps and 300 Mbps), there are other newer additions to Serial ATA that will drastically improve hard drive performance.

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