- Computer Instructions:
- Computer Instruction = instruction/command that a computer will execute
- The Instruction Execution unit of
a computer:
- Central Processing Unit (CPU) =
the component inside
a computer that
execute
computer instructions
Schematic representation of a computer:
The CPU (Central Processing Unit) is depicted on the left hand side
- Central Processing Unit (CPU) =
the component inside
a computer that
execute
computer instructions
- Register:
- Register = a memory device (= data storage) inside the CPU used to store operands and results of computer instructions
Every CPU will have a number registers that hold operands of computer instructions and to store results of computer instructions (e.g., add)
- A computer can execute
3 basic "kinds" (categories)
of computer instructions:
- Data copying operations:
- Some data is
transfered (copied) from
a source location to
a destination location
There are 2 kind of data transfer:
- Load data: the data is copied from a memory location to a register inside the CPU
- Store data: the data is copied from a register inside the CPU to a memory location
- Some data is
transfered (copied) from
a source location to
a destination location
- Arithmetic/logical operations:
- Values from 1 or 2 source registers (inside the CPU) are combined (e.g., negation, add, subtract, multiply, etc) and the result of operation is stored in a destination register
- Branch (with or without linking)
operations:
- A branch operation make the program jump to a different part of the program and continues execution at the branch location
- Data copying operations:
- Comment:
- Some computers has
instructions that
combine
2 (or more) kinds of
basic instructions
Example:
- Intel processors can
execute arithmetic operations
on a value stored in
memory
This kind of instruction is performed by using these basic operations:
- First, the CPU transfer the data from memory into a scratch register(s) inside the ALU
- Then, the CPU performs the Arithmetic/logic operation using values in the scratch register(s) and store the result in (another) register
- Finally, the CPU transfer the result in the register to the memory using another data copying operation
- Intel processors can
execute arithmetic operations
on a value stored in
memory
- Some computers has
instructions that
combine
2 (or more) kinds of
basic instructions