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the processor and main memory
chapter 4,chapter 4,Exploring the Digital DomainExploring the Digital Domain
The Development and Basic Organization of Computers
based on stored program design
Processor memory input/output system
– input/output devices
– secondary storage
Electronic Digital Computers
Processor
manages the instruction-execution cycle FETCH – DECODE – EXECUTE coordinates the activities of other devices
The Processor
(fast access) storage device for preserving binary data and instructions
memory is divided into units or words each is usually a standard size or fixed-
length each memory word has a unique address for
random access
Main Memory
Random Access Memory (RAM)– readable
– writable
– usually volatile (e.g., Dynamic RAM or DRAM)
– general storage
Read Only Memory (ROM)– readable
– permanent
– nonvolatile
– special-purpose storage for data and instructions
Main Memory
Temporary Holding Locations inside the Processor
Let us talk about temporary holding locations inside the processor
These locations can hold “address” or “data” or “instruction” while the same is being used
For example, when we want to read the value stored at a memory location, we use an address
This address is held in a processor register while it is being applied to the memory’s address decoding logic
The Processor and Main Memory
Some Registers
PC: Always holds the address of the next instruction to be executed
MAR: Always used by the processor when addressing the memory
MDR: Data from the memory arrives here first IR: Instruction is held here while it is decoded
and executed ACC: Scratch Register for ALU
Inside the Processor
memoryaddressregister
memoryaddressregister
Inside the Processor
memoryaddressregister
memoryaddressregister
memorydataregister
memorydataregister
Inside the Processor
memoryaddressregister
memoryaddressregister
memorydataregister
memorydataregister
programcounter
programcounter
Inside the Processor
memoryaddressregister
memoryaddressregister
instructionregister
instructionregister
memorydataregister
memorydataregister
programcounter
programcounter
Inside the Processor
memoryaddressregister
memoryaddressregister
instructionregister
instructionregister
memorydataregister
memorydataregister
programcounter
programcounter
arithmeticlogic unit
arithmeticlogic unit
Inside the Processor
memoryaddressregister
memoryaddressregister
instructionregister
instructionregister
memorydataregister
memorydataregister
programcounter
programcounter
accumulator(workregister)
accumulator(workregister)
arithmeticlogic unit
arithmeticlogic unit
Inside the Processor
memoryaddressregister
memoryaddressregister
instructionregister
instructionregister
memorydataregister
memorydataregister
programcounter
programcounter
accumulator(workregister)
accumulator(workregister)
arithmeticlogic unit
arithmeticlogic unitsystem
clocksystemclock
Inside the Processor
1. address of thenext instruction istransferred fromPC to MAR
2. the instruction islocated in memory
1. address of thenext instruction istransferred fromPC to MAR
2. the instruction islocated in memory
FETCH the instruction
3. instruction iscopied frommemory to MDR
3. instruction iscopied frommemory to MDR
FETCH the instruction
instruction istransferred to and decoded inthe IR
instruction istransferred to and decoded inthe IR
DECODE the instruction
control unitsends signalsto appropriatedevices to causeexecution of theinstruction
control unitsends signalsto appropriatedevices to causeexecution of theinstruction
EXECUTE the instruction
Execute the Instruction
The instruction is executed in the ALU
ALU is a 2-input single output unit that can accept one or two operands and produce a result
Data Movement Operations– moving data from
memory to the CPU
– moving data from memory to memory
– input and output
Arithmetic and Logical Operations– integer arithmetic
– comparing two quantities
– shifting, rotating bits in a quantity
– testing, comparing, and converting bits
Types of Processor Operations
Program Control– starting a program
– halting a program
– skipping to other instructions
– testing data to decide whether to skip over some instructions
Types of Processor Operations
