1. Computer Organization, Bus Structure
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2. Computer Organization, Bus Structure
A communication pathway connecting two or more devices
When a word of data is transferred between units all its bits are transferred in parallel
ie. The bits are transferred simultaneously over many lines, one bit per line.
A group of lines that serves as a connecting path for several devices is called a bus
A group of lines connected to different devices is called bus.
 Bus can carry data and control signals
 Single bus – simple way to interconnect functional units.
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3. Computer Organization, Bus Structure
Single Bus Structure
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4. Computer Organization, Bus Structure
All units are connected to this bus
Bus can used only for one transfer at a time
So only 2 units can actively use the bus at any given time.
Only one device at a time can successfully transmit.
Single bus – low cost and It is flexible for attaching diff devices
By using multiple bus simultaneously can transfer more than one data at a time
This leads to increase the performance of the system.
So the bus can carry several data at a time in parallel such as
Power
Instructions
Data
Addresses
Commands
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5. Computer Organization, Bus Structure
Multiple-Bus Organization
The following Figure shows a three-bus structure.
All registers are combined into a single block called register file with three ports: 2 outputs allowing 2 registers to be accessed simultaneously.
Buses A and B are used to transfer source operands to the A and B inputs of ALU, and result transferred to destination over bus C.
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6. Computer Organization, Bus Structure
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7. Computer Organization, Bus Structure
Diff units in a system having diff speed
Keyboard
Printer are relatively slow
some units are very fast all these devices communicate with each other over the same bus
in order to communicate all types of units smoothly include buffer registers with the devices to hold the data during transfer.
 eg transfer of data between processor and printer
Processor sent data over the bus to printer buffer
Once the buffer is loaded the printer can start printing With out the interaction of the processor
The bus and processor are now free to do another work.
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