Buy Pink Computer
Computer Buses
Interfacing to the Personal ComputerIntroduction to Interface Buses found on the personal computer. What makes up a PC interface, with descriptions of each of the common buses found on a modern PC. Links are included to provide more technical information and signal assignments [pin-outs] if additional detail is required.The text also identifies which buses or interfaces are new and which interfaces are older or should be replaced. Also what to look for when purchasing a new computer and which interfaces to avoid.
Introduction
There are three general classes of interfaces used with a Personal Computer. Cable Buses which are found on the out-side of the computer case. Expansion Buses which are located inside the PC case. Motherboard Buses which are local to the motherboard itself are the third type of computer bus.The user accessible connectors at the rear of the PC case are color coded to differentiate the many functions or interfaces available . Except for the audio output jacks which provide left and right speaker connections, all the different interfaces use a completely unique style of connector making it all but impossible to connect the wrong peripheral device into the incorrect mating connector. By default most of the user accessible connections at the rear of the PC accommodate cable interfaces, note the different colored rear panel connectors in the graphic of the PC chassis below.
Cable Buses
![]() |
| PC Rear Panel |
Serial Port
Although not part of this computer [to the left], the most common serial interface used![]() |
| RS232 |
Parallel Port
The primary function of the parallel port was as a printer port. The printer port is visible in both the computer back panel [above] and mother board [shown below] as the long red connector.![]() |
| DB25 Cable |
COM Port
![]() |
| RJ-45 Connector |
Universal Serial Bus
| USB Thumb Drive |
![]() |
| USB Floppy |
Video Interfaces
![]() |
| HD Graphics and TV Tuner Card[1] |
![]() |
| DVI Connector Styles |
PS2 Ports
The PS2 ports on a PC are found as two circular DIN connectors on the rear I/O panel of the PC. There are normally two side-by-side connectors. One connector is used to interface the keyboard and one connector used to interface to a mouse. Both of these connectors are color coded because they are so similar. The keyboard![]() |
| Serial DIN Ports |
connector is color coded purple and the mouse connector is color coded green. The cables coming off either the keyboard or mouse are also color coded using the same scheme. As noted, many new devices may utilize USB interfaces, so the key board or mouse may have USB connectors at the end of the cable and not use either of the two PS-2 connectors, although they still may reside on the PC cut-out. [PS2 Graphic[2]]
Signal Assingments: Keyboard pin out, and Mouse Pinout.
Audio Interfaces
There are a number of audio interfaces on a personal computer, but three main types. The Mic/Line In, Speakers, and in some cases an S/PDIF interface. Each interface is color coded to insure that the correct cable is input to![]() |
| PC Sound Card |
An S/PDIF connection is very common on many PCs to trasmit digital audio and may be found as either an electrical connection [RCA cable] or an optical connection [TOSLINK]. Because S/PDIF is a single line [electrical or optical] there is no pinout for this interface.
Hard Drive Interface
![]() |
| IDE Cable Diagram |
As reference a graph of Google search trends is provided showing the decline in 'IDE' searches between 2004
and 2010. The last version of the IDE standard was released in 2005, while the SATA interface standard was released in 2001. Unfortunately the term IDE is short so other phrases may be using the same three letters to signify something other than a hard drive bus.Expansion Buses
PC Expansion Bus, as the term implies, is a bus that expands the Personal Computer's internal interface bus. The PC Expansion buses are used to add addition PC cards to the system. These interfaces reside on the motherboard and appear as card slots.The common reference to a PC Expansion bus refers to expanding to, or adding functionality to the normal internal computer bus. So the term PC Expansion Bus refers to the additional expansion bus slot residing on the PC's Motherboard.
Most motherboards produced will contain Expansion slots, or connectors to accept additional cards to enhance the computers functionality. However, the type of expansion slot will vary depending on the age or function of the motherboard. Check the product specifications to determine the type and number of expansion slots.
Computer motherboards produced in 2005 have a combination of PC Expansion buses, with 1 or 2 connector slots using PCIe for Video cards, and 2 to 4 slots for a PCI Boards. The PCI interface has been around for a number of years and has a larger base than PCIe. There are many PCI cards that have been developed to provide a number of functions, while low end PCIe cards are just now coming out [because the motherboards don't have PCIe 1x slots].
![]() |
| Personal Computer Mother-Board |
PCI Interface
The Peripheral Component Interface [PCI] slot is used as a general purpose expansion slot used on almost all motherboards produced in the last ten years. Four PCI expansion slots are shown in the computer motherboard picture to the left, as four vertical white connectors. The PCI expansion slot can still be found next to the more current PCIe slot on motherboards currently be shipped.AGP Interface
The Accelerated Graphics Port [AGP] slot is used to accept a Video card. The AGP expansion slot is an enhanced version of a PCI bus developed specifically as a video interface. The single brown connector in the center of the motherboard graphic is an AGP interface. Most new PCs shipped no longer contain an AGP slot which have now been replaced by the PCIe interface [below]. However; AGP cards are still widely used in the up-grade market. The latest revision of the AGP interface is revision 3.0 or AGP 8x [as of 2002]. Note that rev 3.0 will be the last and final upgrade to the AGP specification. The AGP standard is out-dated.PCIe Interface
![]() |
| PCIe Expansion Slot |
![]() |
| DIMM Module |
Motherboard Buses
![]() |
| AMD Phenom Quad-Core uP Die |
The Front-side bus is the main electrical interface into the micro-processor via the Northbridge. The Northbridge also interfaces to the video expansion slot
![]() |
| AMD 64 FX Processor |
There have been three companies that produce uP's for personal computers; Intel, AMD and IBM. Up until a few years ago Apple computers used an IBM processor, now Apple Computer uses an Intel processor. IBM compatible PCs will use either an AMD or Intel processor.
Bus Upgrades
![]() |
| Disk Drive Transfer Rates by Year of Standard Release |
More importantly the USB interface is currently under going a revision upgrade, from revision 2.0 to 3.0. The original USB interface was released in 1994, and revision 2.0 being released in 2000. However the newest version of the standard was released just last year. So if possible a new computer purchased should include revision 3.0 of the USB bus, even though there are only a few products that currently support the new standard. Another year from now there will be a great number or products on the market that will support rev 3 of the USB standard. It's just like waiting for the next MS OS to be released, instead of paying another ninety dollars a few months later for the upgrade.
Of course these comments only apply to the time frame immediately surrounding the date a specification is in revision. As a general rule many of these interface standards are being updated about every three or four years. But when you account for the number of different standards and the fact that they are unrelated and do not get updated relative to one another than on any given year there could be at least one computer related specification coming out with a new revision.
Insuring that the latest bus specification is purchased does not incur the same increase in cost as purchasing the next generation CPU. The newest processor might come with a severe premium of several hundred dollars over the cost of a processor that was released just a few months prior. Normally a chip set for an interface bus costs little more than the previous generation of the interface.
Yet another new standard about to be released is the Universal Flash Storage [UFS] card. The specification is not due out until the end of 2010, and products wouldn't be available until 2011 at a minimum. Still it's a new interface that would be found on computers with Card Reader modules; however the specification is really aimed at embedded storage for cameras and cell phones [just like an SD Card].
Acronyms not defined in text: AMD; Advanced Micro Devices
DIN; Deutsches Institut fr Normung. A German national standards organization
IBM; International Business Machines
LPT; Line Print Terminal
RCA; Radio Corporation of America
S/PDIF; Sony/Philips Digital Interface
TOSLINK; TOShiba-LINK, a registered trademark of Toshiba Corporation
Many more Engineering Related Electronic Acronyms. This link is off-site..
Additional Knols related to computers;Description of Solid State Drives. [What is an SSD and do I want one] Interfacing to a Secure Digital Card. [SD Card Issues]Adding Permanent Memory via a USB Stick. [USB ReadyBoost implementation]The RS232 Interface. [RS232 Tutorial and its continuing usage decline]Generation of PC Standards. [Who controls the definition of a PC]
Helpful Links;Companies that produce Computers.Companies that produce Laptop PCs.Companies that manufacturer and sell PC Monitors.
Editor note; this text uses two graphics of AMD processors, but that does not imply support for PC's using AMD devices. It just happens that there were AMD graphics available for use in the article. Some years AMD has faster processors, while other years Intel has faster processors, it really changes every other year.
25 Days of Christmas Crafts: Computer Keyboard Notebook (NERD ALERT II)
Breaking the Fast at Ramadan
Next page: Nickelodeon Moon Shoes















.jpg)







