marie:an introduction to a simple computer michael dougherty 4.1 - 4.5 september 17, 2009
TRANSCRIPT
MARIE:An Introduction to a Simple Computer
Michael Dougherty
4.1 - 4.5
September 17, 2009
Central Processing Unit
CPUFetches Program InstructionsDecode Each InstructionPerform Operation
Divided into two partsDatapathControl Unit
Datapath
Registers
ALUs
Buses
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Registers
D Flip-Flops can be used as registersA clock pulse controls access to the data
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Registers
Registers have a fixed “word” size
Number of registers are usually a power of 2Special Purpose
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ALU
Performs the operations such as comparisons, adding, and multiplying
Generally has two data inputs and one data output
These operations often affect bits in the status register
A Simple ALU circuit
Control Unit
Sequences operations
Ensures data is at the correct place at the correct time
The BUS
The wires that connect the CPU to other components
Only one item at a time can use the bus
Speed is affected by length and number of devices sharing it.
Point-to-point bus
Point-to-point bus connects two specific devices
Common pathway
Common pathway connects a number of devices
“Multipoint” bus
Bus Protocol
Data bus
Control lines
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Address lines
Power lines
Data Bus
Data bus - the actual information to move from one location to another
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Control lines
Control lines - tell which device has permission to use the bus and for what.
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Address lines
Address lines - the location in memory that the data should be read from or written to.
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Power lines
Power lines - provides the power to the circuitry.
Bus Types
Processor-memory Buses I/O Buses Backplane Bus Personal Computer Buses
Internal Bus (System Bus) External Bus Local Bus
Just Some Wires?
Synchronous buses
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Asynchronous buses
Handshaking ProtocolReqREADReadyDATAACK
Bus arbitration
Daisy Chain Arbitration
Centralized Parallel Arbitration
Distributed Arbitration using self-selection
Distributed arbitration using collision detection
Clocks
Speed
Clock cycles
Clock Frequencies (MHz or GHz)
Clock Cycle TimeBus clocks
Overclocking
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Speed vs. Performance
Same clock speed ≠ same performance Intel 286
PentiumQuickTime™ and a
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Overclocking
Pushes manufacturer’s time constraints
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The I/O Subsystem
Most familiar items of computer
Not connected directly to the CPUMemory-mapped I/O
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Instruction-based I/O
No memory use
Limited CPUs can use devices