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Digital Computer Organization - Discussion
ALU: Arithmetic Logical Unit

A most generic computer system is composed of a unit to do arithmetic, shift and logical micro-operations commonly know as ALU of CPU.
General Purpose Registers: R1, R2, R3.
As the name General Purpose Registers, suggests that the registers are involved in operations like load inputs, store intermediate results of arithmetic, logical and shift micro-operations. The initial inputs are loaded into registers from memory and final results are later moved into memory.

ACC: Accumulator
This block acts as the default temporary storage register location for all mathematical operations in ALU.
Timing and Control unit:
This block manages the sequencing of events on a timeline between various components of a CPU. All the blocks are controlled in a manner to optimize the computational power of the unit by minimizing the failures.

Flags are also registers or bits inside registers which are set or cleared for a particular condition on an arithmetic operation. some of the most common flags are:
Sign - Is used to identify the set/reset of most significant bit of the result.
Carry - Is used to identify, a carry during addition, or borrow during subtraction/comparison.
Parity - set if the parity is even. Refer parity from here.
Zero - to identify when the result is equal to zero.
Bus sub-system.
All the data transfers in-between memory and CPU registers including instruction fetches are carried over bus.
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Instruction Register IR and Decoder:
After instruction is fetched from the memory its stored in Instruction Register. The instruction is then decode by the decoder.

Stack Pointer (SP):
Stack Pointer is involved in managing the Stack transfers during and program execution. Refer details on stack organization from here.
We will discuss the Digital Computer Organization in details on this page. Main components covered are ALU, Program Counter (PC), Registers, Stack Pointer (SP), stack, timing control unit and flags.

Block diagram of CPU is discussed on previous page.
Program counter:
This keeps track of the instruction address in memory from where the next instruction needs to be fetched. The instructions are stored in memory in an order decided by programmer.
Detailed discussion on computer. ALU operations can be accessed from here.
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