CS-350 TERM PROJECT

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CS-350 TERM PROJECT COMPUTER BUSES By
AJIT UMRANI
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What is a Bus ?
A bus is a data communications connection between
two or more communicating devices.
What Does a Bus carry?

1. Electrical Power.
2. Control Signals.
3. Memory Address.
4. Data.

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Different Buses
Buses that work in sync with CPU and system clock
are called the local buses or system buses.
Buses that work asynchronously with the CPU are
called the expansion buses. Ex. The memory bus
is a local bus while the ISA bus is an expansion
bus.
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Bus Evolution
Bus Released Bus Speed (MHz)
ISA (8 Bit) 1982 4.77
ISA (8 Bit) 1984 8.33
MCA 1987 10
EISA 1988 8.33
VL-bus v1.0 1992 33
VL-bus v2.0 1994 50
PCI v1.0 1993 33
PCI v2.0 1994 66 
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ISA (8 Bit) Buses

• used in the first 4.77-MHz PCs introduced in
  1982.
• 62 - Pin Bus.
• 8 Data Lines (allowing for 8 bits of data to be
  transferred at a time).
• 20 address lines (1 Mbytes of addressing ).

ISA (16 Bit) Buses

• 8.33-MHz Bus introduced in 1984.
• 62 36 - Pin Bus.
• Eight more data lines (allowing for 16-bit data
  transfers).
• Four more address lines (allowing 16 Mbytes of
  addressing).

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MCA Buses Micro Channel Architecture Buses

• The 32-bit bus. Introduced in 1987.
• It runs at 10 MHz.
• The theoretical maximum data transfer rate is
  40 Mbytes/s.
• support for video and audio.

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EISA Extended Industry Standard Architecture

• Developed by the "Gang of Nine" (nine non-IBM
  manufacturers of IBM-compatible PCs, led by
  Compaq) in 1988.
• 32 Bit Bus.
• Runs at 8.33 MHz.
• The theoretical maximum transfer speed is 33
  Mbytes/s.
• A main advantage over MCA is that ISA boards can
  be plugged into the EISA bus.

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VESA Video Electronics Standards Association

• Introduced in 1992 as a Standard for 32-Bit
  Local Buses.
• It runs at 33 MHz.
• It uses a 32 Bit Expansion slot.
• Has been replaced by the PCI buses.

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PCI Buses Peripheral Component Interconnect Buses

• 32 or 64-bit wide bus implementations.
• It Runs at 33 MHz. Newer versions Run at 66 MHz.
• Maximum Theoretical transfer rate is 264
  Mbytes/s.
• Designed to support ISA and EISA buses.
• It interfaces the expansion bus and the memory
  bus.

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Relatively New Buses
USB ( Universal Serial Bus ) Allows 2 speeds
1.5 Mbit/s and 12 Mbit/s. Replacing the slow
serial and parallel ports. FireWire Bus Data
Speeds as high as 400 Mbit/s. Replacing the High
speed, High volume peripheral devices like
network cards, DVD etc. AGP ( Accelerated
Graphical Port ) Has 32 Bit Data path and Run
at Memory Bus Speed. Designed to provide fast
access to video. Has replaced VESA PCI Buses
for Video output.
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Bus Speed and Overall Performance
Bus or Device Typical Values
CPU 500 MHz, fastest ones are 1.7 GHz
Memory Bus Speed 66 MHz, Some claim up speeds to 200MHz
PCI Bus 33 MHz, Generally is Half the Memory Bus Speed
ISA Bus 8.77 MHz