A control unit is the part of a CPU or other device that directs its operation. The outputs of the unit control the activity of the rest of the device. A control unit can be thought of as a finite state machine.
The control unit is the circuitry that controls the flow of data through the processor, and coordinates the activities of the other units within it. In a way, it is the "brain within the brain", as it controls what happens inside the processor, which in turn controls the rest of the PC.
A few examples of devices that need a control unit are CPUs, Graphics Cards, Network Interfaces, Hard Drives, Bus Controllers (USB, PCI, Firewire, etc. ). The modern information age would not be possible without complex control unit designs.
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Hardwired Control
At one time control units for CPUs were ad-hoc logic, and they were difficult to design. This can be identified as the main part of the computer and the main device that helps the computer to function in an appropriate manner.
Microprogram Control
Now they are often implemented as a microprogram that is stored in a control store. Microprogramming (ie writing microcode) is a method that can be employed to implement Machine instructions in a CPU relatively easily often using less Microprogramming (ie writing microcode) is a method that can be employed to implement Machine instructions in a CPU relatively easily often using less A control store is the part of a CPU's Control unit that stores the CPU's Microprogram. Words of the microprogram are selected by a microsequencer and the bits from those words directly control the different parts of the device, including the registers, arithmetic and logic units, instruction registers, buses, and off-chip input/output. In Computer architecture and Engineering, a sequencer or microsequencer is a part of the Control unit of a CPU. In Computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage In Computing, an arithmetic logic unit ( ALU) is a Digital circuit that performs Arithmetic and Logical operations In Computing, an instruction register is the part of a CPU 's Control unit that stores the instruction currently being executed In Computer architecture, a bus is a subsystem that transfers data between computer components inside a Computer or between computers In Computing, input/output, or I/O, refers to the communication between an Information processing system (such as a Computer) and the outside In modern computers, each of these subsystems may have its own subsidiary controller, with the control unit acting as a supervisor.
Functions of the Control Unit
The functions performed by the control unit vary greatly by the internal architecture of the CPU, since the control unit really implements this architecture. On a regular processor that executes x86 instructions natively the control unit performs the tasks of fetching, decoding, managing execution and then storing results. On a processor with a RISC core the control unit has significantly more work to do. It manages the translation of x86 instructions to RISC micro-instructions, manages scheduling the micro-instructions between the various execution units, and juggles the output from these units to make sure they end up where they are supposed to go. On one of these processors the control unit may be broken into other units (such as a scheduling unit to handle scheduling and a retirement unit to deal with results coming from the pipeline) due to the complexity of the job it must perform.
See also
CPU design is the Design engineering task of creating a Central processing unit (CPU a component of Computer hardware. In Computer engineering, computer architecture is the conceptual design and fundamental operational structure of a Computer system The Richard’s Controller is a method of implementing a Finite state machine using simple integrated circuits and combinational logicDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic