Multilevel viewpoint of a machine

Micro-Architecture / Control unit

Level 1

Micro-Architecture / Control unit

• This is a collection of 8 to 32 registers for memory and ALU to perform arithmetic and logical operations.

• This level contains a micro program which fetches, decode and execute instructions.

• Resistors are connected to the ALU to form a data path, over which data flow.

• The operation of the data path may be controlled by a micro program, directly by hardware((hardware) i.e, is hardwired).

Computer Architecture is the combination of micro architecture and instruction set design.

Hardwired control:

• Hardwired control unit consists of hardware that directly executes machine instructions.

• The control logic is implemented Decoder, Gates, flip flops and other digital circuits.

• It can be optimised to produce a fast mode of operation.

• Making any change is quite difficult in this.

Microprogrammed control Unit:

Microprogrammed control unit is build around a storage unit called control memory where all control signals are stored in program like format.

• Control memory stores a set of micro program which are designed to implement instruction set.

• Each Instruction causes a set of microprogram to be fetched.

• And its control information is extracted in a manner that resembles the fetching and execution of program from main memory.

• Design can be changed easily by just updating the contents of the control memory.

• Basically a micro program is a program written in a low level language that is implemented by the hardware.

12- Multilevel Viewpoint Of A Machine- Micro Architecture


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