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The CPU is connected to the rest of the system through system bus. Through system bus, data or information gets
transferred between the CPU and the other component of the system. The system bus may have three components:
Data Bus
Data bus is used to transfer the data between main memory and CPU.
Address Bus: Address bus is used to access a particular memory location by putting the address of the memory location. Control Bus:
Control bus is used to provide the different control signal generated by CPU to different part of the system. As for example, memory read is a signal generated by CPU to indicate that a memory read operation has to be performed. Through control bus this signal is transferred to memory module to indicate the required operation. There are three basic components of CPU: register bank, ALU and Control Unit. There are several data movements between these units and for that an internal CPU bus is used. Internal CPU bus is needed to transfer data between the various registers and the ALU, because the ALU in fact operates only on data in the internal CPU memory.
Register Organization
A computer system employs a memory hierarchy. At the highest level of hierarchy, memory is faster, smaller and more expensive. Within the CPU, there is a set of registers which can be treated as a memory in the highest level of hierarchy. The registers in the CPU can be categorized into two groups:
● User-visible registers: These enables the machine - or assembly-language programmer to minimize main memory reference by optimizing use of registers.
● Control and status registers: These are used by the control unit to control the operation of the CPU. Operating system programs may also use these in privileged mode to control the execution of program.
User-visible Registers: The user-visible registars can be categorized as follows:
❍ General Purpose Registers
❍ Data Registers
❍ Address Registers
❍ Condition Codes
Data bus is used to transfer the data between main memory and CPU.
Address Bus: Address bus is used to access a particular memory location by putting the address of the memory location. Control Bus:
Control bus is used to provide the different control signal generated by CPU to different part of the system. As for example, memory read is a signal generated by CPU to indicate that a memory read operation has to be performed. Through control bus this signal is transferred to memory module to indicate the required operation. There are three basic components of CPU: register bank, ALU and Control Unit. There are several data movements between these units and for that an internal CPU bus is used. Internal CPU bus is needed to transfer data between the various registers and the ALU, because the ALU in fact operates only on data in the internal CPU memory.
Register Organization
A computer system employs a memory hierarchy. At the highest level of hierarchy, memory is faster, smaller and more expensive. Within the CPU, there is a set of registers which can be treated as a memory in the highest level of hierarchy. The registers in the CPU can be categorized into two groups:
● User-visible registers: These enables the machine - or assembly-language programmer to minimize main memory reference by optimizing use of registers.
● Control and status registers: These are used by the control unit to control the operation of the CPU. Operating system programs may also use these in privileged mode to control the execution of program.
User-visible Registers: The user-visible registars can be categorized as follows:
❍ General Purpose Registers
❍ Data Registers
❍ Address Registers
❍ Condition Codes
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