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Q. With appropriate diagrams explain the bus structure of a computer system?


BUS structure : A group of lines that serves as a connecting path for several devices is called bus.In addition to the lines that carry the data, the bus must have lines for address and control purposes.

In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers

A computer bus structure is provided which permits replacement of removable modules during operation of a computer wherein means are provided to precharge signal output lines to within a predetermined range prior to the usage of the signal output lines to carry signals, and further, wherein means are provided to minimize arcing to pins designed to carry the power and signals of a connector. In a specific embodiment, pin length, i.e., separation between male and female components of the connector, are subdivided into long pin length and short pin length. Ground connections and power connections for each voltage level are assigned to the long pin lengths. Signal connections and a second power connection for each voltage level is assigned to the short pin lengths. The precharge/prebias circuit comprises a resistor divider coupled between a power source and ground with a high impedance tap coupled to a designated signal pin, across which is coupled a charging capacitor or equivalent representing the capacitance of the signal line. Bias is applied to the precharge/prebias circuit for a sufficient length of time to precharge the signal line to a desired neutral signal level between expected high and low signal values prior to connection of the short pin to its mate..

Early computer buses were literally parallel electrical buses with multiple connections, but the term is now used for any physical arrangement that provides the same logical functionality as a parallel electrical bus. Modern computer buses can use both parallel and bit-serial connections, and can be wired in either a multidrop (electrical parallel) or daisy chain topology, or connected by switched hubs, as in the case of USB.

 

Description of BUS :

At one time, "bus" meant an electrically parallel system, with electrical conductors similar or identical to the pins on the CPU. This is no longer the case, and modern systems are blurring the lines between buses and networks.

Buses can be parallel buses, which carry data words in parallel on multiple wires, or serial buses, which carry data in bit-serial form. The addition of extra power and control connections, differential drivers, and data connections in each direction usually means that most serial buses have more conductors than the minimum of one used in the 1-Wire and UNI/O serial buses. As data rates increase, the problems of timing skew, power consumption, electromagnetic interference and crosstalk across parallel buses become more and more difficult to circumvent. One partial solution to this problem has been to double pump the bus. Often, a serial bus can actually be operated at higher overall data rates than a parallel bus, despite having fewer electrical connections, because a serial bus inherently has no timing skew or crosstalk. USB, FireWire, and Serial ATA are examples of this. Multidrop connections do not work well for fast serial buses, so most modern serial buses use daisy-chain or hub designs.

Most computers have both internal and external buses. An internal bus connects all the internal components of a computer to the motherboard (and thus, the CPU and internal memory). These types of buses are also referred to as a local bus, because they are intended to connect to local devices, not to those in other machines or external to the computer. An external bus connects external peripherals to the motherboard.

Network connections such as Ethernet are not generally regarded as buses, although the difference is largely conceptual rather than practical. The arrival of technologies such as InfiniBand and HyperTransport is further blurring the boundaries between networks and buses. Even the lines between internal and external are sometimes fuzzy, I²C can be used as both an internal bus, or an external bus (where it is known as ACCESS.bus), and InfiniBand is intended to replace both internal buses like PCI as well as external ones like Fibre Channel. In the typical desktop application, USB serves as a peripheral bus, but it also sees some use as a networking utility and for connectivity between different computers, again blurring the conceptual distinction.

 

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