Bus Slots In Computer

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In computing, a bus is defined as a set of physical connections (for example, cables, printed circuits, etc.) that can be shared by multiple hardware components in order to communicate with one another. The purpose of buses is <boldWto reduce the number of pathways needed for communication</bold> between the components, by carrying out all communications over a single data channel. This is why the metaphor of a data highway is sometimes used.

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The 220-700 series A+ exam has been retired! See my new CompTIA A+ videos: An important consideration of the very first IBM personal. Alternatively referred to as a bus slot or expansion port, an expansion slot is connection or port located inside a computer on the motherboard or riser board that allows a.




Characteristics

If only two hardware components communicate over the line, it is called a hardware port, (such as a port or parallel port).

There are different types of computer buses. A bus is characterized by the amount of information that can be transmitted at once. This amount, expressed in bits, corresponds to the number of physical lines over which data is sent simultaneously. A 32-wire ribbon cable can transmit 32 bits in parallel. The term width is used to refer to the number of bits that a bus can transmit at once.

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Additionally, the bus speed is defined by its frequency (expressed in Hertz), the number of data packets sent or received per second. Each time that data is sent or received is called a cycle.

It is possible to find the maximum transfer speed of the bus, or the amount of data that it can transport per unit of time, by multiplying its width by its frequency. For example, a bus with a width of 16 bits and a frequency of 133 MHz has a transfer speed equal to:

Architecture

In reality, each bus is generally constituted of 50 to 100 distinct physical lines, divided into three subassemblies:

  • The address bus: sometimes called the memory bus, it transports memory addresses that the processor wants to access in order to read or write data. It is a unidirectional bus.
  • The data bus: it transfers instructions coming from or going to the processor. It is a bidirectional bus.
  • The control bus, or the command bus: it transports orders and synchronization signals coming from the control unit and traveling to all other hardware components. It is a bidirectional bus, as it also transmits response signals from the hardware.

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The Primary Buses

There are generally two buses within a computer.

  • The internal bus: sometimes called the front-side bus, or FSB for short, it allows the processor to communicate with the system's central memory (the RAM).
  • The expansion bus: sometimes called the input/output bus, it allows various motherboard components (namely, USB, serial, and [contents/415-serial-port-and-parallel-port parallel ports], cards inserted in PCI connectors, hard drives, CD-ROM and CD-RW drives, etc.) to communicate with one another. However, it is mainly used to add new devices using what it’s called expansion slots connected to the input/output bus.

Motherboard Chipset

What is “chipset”? A chipset is the component that routes data between the computer's buses, so that all the components that make up the computer can communicate with each other. The chipset originally was made up of a large number of electronic chips, hence the name.

It generally has two components. The first is the NorthBridge (also called the memory controller) that is in charge of controlling transfers between the processor and the RAM; this is the reason why it is located physically near the processor. It is sometimes called the GMCH, for Graphic and Memory Controller Hub.

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The second is the SouthBridge (also called the input/output controller or expansion controller) that handles communications between peripheral devices. It is also called the ICH (I/O Controller Hub). The term bridge is generally used to designate a component that connects two buses:


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It is noteworthy that, in order to communicate, two buses must have the same width. This explains why RAM modules sometimes have to be installed in pairs (for example, early Pentium chips, whose processor buses were 64-bit, required two memory modules each 32 bits wide).

Here is a table that gives the specifications for the most commonly used buses:
StandardBus width (bits)Bus speed (MHz)Bandwidth (MB/sec)
ISA 8-bit88.37.9
ISA 16-bit168.315.9
EISA328.331.8
VLB3233127.2
PCI 32-bit3233127.2
PCI 64-bit 2.16466508.6
AGP3266254.3
AGP (x2 Mode)3266x2528
AGP (x4 Mode)3266x41056
AGP (x8 Mode)3266x82112
ATA33163333
ATA1001650100
ATA1331666133
Serial ATA (S-ATA)1180
Serial ATA II (S-ATA2)2380
USB11.5
USB 2.0160
FireWire1100
FireWire 21200
SCSI-184.775
SCSI-2 - Fast81010
SCSI-2 - Wide161020
SCSI-2 - Fast Wide 32 bits321040
SCSI-3 - Ultra82020
SCSI-3 - Ultra Wide162040
SCSI-3 - Ultra 284040
SCSI-3 - Ultra 2 Wide164080
SCSI-3 - Ultra 160 (Ultra 3)1680160
SCSI-3 - Ultra 320 (Ultra 4)1680 DDR320
SCSI-3 - Ultra 640 (Ultra 5)1680 QDR640

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The PCI expansion slot was introduced by Intel, but can be found in both PC's and Macs. It displaced previous computer buses (VESA Local Bus and ISA). PCI was then succeeded by the PCI-E or (PCI Express slot), but PCI is still found in most computers because many expansion devices don't need PCI-E capabilities.

It is also possible to get a PCI card that had more PCI expansion slots on it. This would be helpful for a computer that did not have enough PCI expansion slots for further expansions, although most computers would have an ample amount of slots.

When choosing a computer case, it is a good idea to choose a case that will allow for a bigger enough case so as to have a suitable amount of PCI expansion slots. This can be very useful if you want to add some cards later, such as a wireless card, or some more USB slots, or a TV tuner?

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PCI Express
PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe, is a high-speed serialcomputerexpansion bus standard designed to replace the older PCI, PCI-X, and AGP bus standards. PCIe has numerous improvements over the older standards, including higher maximum system bus throughput, lower I/O pin count and smaller physical footprint, better performance scaling for bus devices, a more detailed error detection and reporting mechanism (Advanced Error Reporting, AER[1]), and native hot-plug functionality. More recent revisions of the PCIe standard provide hardware support for I/O virtualization.


PCI EXPRESS X 16

PCI Express x16 (graphics): PCI Express x16 slots are used mostly for graphics cards, though they can be used with any PCI Express card. Confusion may arise, however, because not all PCIe x16 slots are true PCIe x16. Occasionaly, you'll see PCIe x16 connectors that are physical slots for accommodating graphics cards, but are actually eight-lane (x8) or even four-lane (x4) electrically.

On some boards, even slots that support true 16-lane PCI Express for graphics may revert to eight lanes if you install a second graphics card into a second PCIe x16 slot on the motherboard. The P67 chipset, for instance, has only 16 total PCIe lanes for graphics. So if you drop in two graphics cards to run in dual GPU mode, each card will have just eight lanes available to it. This situation isn't as bad as it sounds, though, since even eight lanes in a PCIe 2.0- or 3.0-based system delivers plenty of bandwidth for most games


Bus Slots In Computer