Bus Slots In Computer
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.
An expansion bus is an assortment of wires that allows for computer expansion with the use of an expansion board, a printed circuit board inserted into an expansion slot on the motherboard or backplane that provides additional features to a computer system. A Bus in a computing system is somewhat like a bus on which you travel. Of course, it’s not a pun, a BUS in a computer works in a collection of wires through which all the data can be transmitted from any part of the computer to another. In other words, it is a connection between many computer parts to enable you operates your system efficiently.
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.
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
Bus Slots In Computer Game
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.
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).
| Standard | Bus width (bits) | Bus speed (MHz) | Bandwidth (MB/sec) |
|---|---|---|---|
| ISA 8-bit | 8 | 8.3 | 7.9 |
| ISA 16-bit | 16 | 8.3 | 15.9 |
| EISA | 32 | 8.3 | 31.8 |
| VLB | 32 | 33 | 127.2 |
| PCI 32-bit | 32 | 33 | 127.2 |
| PCI 64-bit 2.1 | 64 | 66 | 508.6 |
| AGP | 32 | 66 | 254.3 |
| AGP (x2 Mode) | 32 | 66x2 | 528 |
| AGP (x4 Mode) | 32 | 66x4 | 1056 |
| AGP (x8 Mode) | 32 | 66x8 | 2112 |
| ATA33 | 16 | 33 | 33 |
| ATA100 | 16 | 50 | 100 |
| ATA133 | 16 | 66 | 133 |
| Serial ATA (S-ATA) | 1 | 180 | |
| Serial ATA II (S-ATA2) | 2 | 380 | |
| USB | 1 | 1.5 | |
| USB 2.0 | 1 | 60 | |
| FireWire | 1 | 100 | |
| FireWire 2 | 1 | 200 | |
| SCSI-1 | 8 | 4.77 | 5 |
| SCSI-2 - Fast | 8 | 10 | 10 |
| SCSI-2 - Wide | 16 | 10 | 20 |
| SCSI-2 - Fast Wide 32 bits | 32 | 10 | 40 |
| SCSI-3 - Ultra | 8 | 20 | 20 |
| SCSI-3 - Ultra Wide | 16 | 20 | 40 |
| SCSI-3 - Ultra 2 | 8 | 40 | 40 |
| SCSI-3 - Ultra 2 Wide | 16 | 40 | 80 |
| SCSI-3 - Ultra 160 (Ultra 3) | 16 | 80 | 160 |
| SCSI-3 - Ultra 320 (Ultra 4) | 16 | 80 DDR | 320 |
| SCSI-3 - Ultra 640 (Ultra 5) | 16 | 80 QDR | 640 |
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What is Computer Bus: The electrically conducting path along which data is transmitted inside any digital electronic device. A Computer bus consists of a set of parallel conductors, which may be conventional wires, copper tracks on a PRINTED CIRCUIT BOARD, or microscopic aluminum trails on the surface of a silicon chip. Each wire carries just one bit, so the number of wires determines the largest data WORD the bus can transmit: a bus with eight wires can carry only 8-bit data words, and hence defines the device as an 8-bit device.
A computer bus normally has a single word memorycircuit called a LATCH attached to either end, which briefly stores the word being transmitted and ensures that each bit has settled to its intended state before its value is transmitted.
The Computer bus helps the various parts of the PC communicate. If there was no bus, you would have an unwieldy number of wires connecting every part to every other part. It would be like having separate wiring for every light bulb and socket in your house.
We’ll be covering the following topics in this tutorial:
Types of Computer Bus
There are a variety of buses found inside the computer.
Data Bus: The data bus allows data to travel back and forth between the microprocessor (CPU) and memory (RAM).
Address Bus: The address bus carries information about the location of data in memory.
Control Bus: The control bus carries the control signals that make sure everything is flowing smoothly from place to place.
Expansion Bus: If your computer has expansion slots, there’s an expansion bus. Messages and information pass between your computer and the add-in boards you plug in over the expansion bus.
Although this is a bit confusing, these different buses are sometimes together called simply “the bus.” A user can think of the computer’s “bus” as one unit made up of three parts: data, address, and control, even though the three electrical pathways do not run along each other (and therefore don’t really form a single “unit”) within the computer.
There are different sizes, or widths of data buses found in computers today. A data bus’ width is measured by the number of bits that can travel on it at once. The speed at which its bus can transmit words, that is, its bus BANDWIDTH, crucially determines the speed of any digital device. One way to make a bus faster is to increase its width;
for example a 16-bit bus can transmit two 8-bit words at once, ‘side-by-side’, and so carries 8-bit data twice as fast as an 8-bit bus can. A computer’s CPU will typically contain several buses, often of differing widths, that connect its various subunits. It is common for modern CPUs to use on-chip buses that are wider than the bus they use to communicate with external devices such as memory, and the speed difference between on- and off-chip operations must then be bridged by keeping a reservoir of temporary data in a CACHE. For example many of the Pentium class of processors use 256 bits for their fastest on-chip buses, but only 64 bits for external links.
An 8-bit bus carries data along 8 parallel lines. A 16-bit bus, also called ISA (Industry Standard Architecture), carries data along 16 lines. A 32-bit bus, classified as EISA (Enhanced Industry Standard Architecture) or MCA (Micro Channel Architecture), can carry data along 32 lines.
The speed at which buses conduct signals is measured in megahertz (Mhz). Typical PCs today run at speeds between 20 and 65Mhz. Also see CPU, Expansion Card, Memory, Motherboard, RAM, ROM, and System Unit.
How Does Computer Bus Work?
A bus transfers electrical signals from one place to another. An actual bus appears as an endless amount of etched copper circuits on the motherboard’s surface. The bus is connected to the CPU through the Bus Interface Unit.
Data travels between the CPU and memory along the data bus. The location (address) of that data is carried along the address bus. A clock signal which keeps everything in synch travels along the control bus.
The clock acts like a traffic light for all the PC’s components; the “green light” goes on with each clock tick. A PC’s clock can “tick” anywhere from 20 to 65 million times per second, which makes it seem like a computer is really fast. But since each task (such as saving a file) is made up of several programmed instructions, and each of those instructions takes several clock cycles to carry out, a person sometimes has to sit and wait for the computer to catch up.