DATA FORMATS
In
selecting the number representation the following factors should be taken into
account:
1. TYPES of NUMBERS to be represented e.g., integers,
real numbers, complex numbers
2. The RANGE of VALUES to be encountered
3. The PRECISION of the NUMBER
4. THE COST of HARDWARE required to store and process
the numbers
INSTRUCTION FORMATS
In
selecting the instruction format(s) the following factors should be considered.
1. The number of instructions to be represented.
2. The addressability and addressing modes.
3. The ease of decoding.
4. Type of instruction field (fixed or variable)
5. The cost of hardware required to decode and
execute instructions.
Instruction formats
Instruction
code is a group of bits that instruct the computer to
perform a specific operation. It is usually divided into parts, each having its
own particular interpretation. The most basic part of an instruction code is
its operation code operation part.
Instructions Types
Computers may have
instructions of several different lengths containing varying number of
addresses. The number of address fields in the instruction format of a computer
depends on the internal organization of its registers. Most computers fall into
one of three types of CPU organizations:
1. General register organization.
2. Single accumulator organization.
3. Stack organization.
Addressing Modes
The most common fields
found in instruction formats are:
Computers use addressing mode techniques for the purpose of
accommodating one or both of the following provisions:
1. To give programming versatility to the user by providing such
facilities as pointers to memory,counters for loop control, indexing of data,
and program relocation.
2. To reduce the number of bits in the addressing field of the
instruction.
- The mode field is used to locate the operands needed for the
operation.
(i.e.A mode field that specifies
the way the operand or the effective address) .
- Operands residing in processor registers are specified with a register
address