Description of Addressing Architecture

1. Memory Addressing
Prof. Neeraj Bhargava
Kapil Chauhan
Department of Computer Science
School of Engineering & Systems Sciences
MDS University, Ajmer

2. Computer Architecture Concepts
• Machine language: binary language
• Assembly language: symbolic language
• In the past, architecture, organization and hardware
are used to descript a computer.
• Due to the higher and higher performance of
computer, the relationships among architecture,
organization and hardware become intertwined.
• Instruction set architecture (ISA) is then used to
encompass the whole of computer.

3. Computer Architecture Concepts
Program Counter (PC) keeps track of the instructions
in the program stored in memory.

4. Addressing Architecture
Memory-to-memory
PC is the only register
21 accesses to memory needed in the previous example
(includes accesses of address, data, instruction)
instruction count is low, but the execution time is
potentially high

5. Addressing Architecture
Register-to-register
allow only one memory address
restrict its use to load and store type
needs sizable register file
see the program on the top of page 522 in textbook
only 18 memory accesses are needed

6. Addressing Architecture
• Register-memory type
– ADD R1, A R1 R1+M[A]←
– program lengths and number of memory accesses tend
to be intermediate between the previous two
architectures
• Single-accumulator architecture
– no register file
– significant additional memory accesses would be
needed for complex programs
– inefficient, is restricted to use in CPUs for simple, low-
cost applications

7. PUSH A
PUSH B
ADD
PUSH C
MUL
PUSH D
PUSH E
MUL
ADD

8. Addressing Mode
Addressing mode: The rule for interpreting or
modifying the address field of an instruction.
Effective address: The address of operand
produced by the application of the rule for
interpreting or modifying the address field of
the instruction before the operand is actually
referenced.

9. Addressing Mode
Implied mode: needs no address field, the operand
is specified implicitly in the definition of the opcode.
For example, ADD in a stack computer.
Immediate mode: an instruction has an operand
field rather than an address field.

10. Addressing Mode
Indirect addressing mode: the address field of
the instruction gives the address at which the
effective address is stored in memory
Relative addressing mode: Effective address=
address part of the instruction + contents of PC
(signed number)

11. Addressing Mode
Indexed addressing mode: the content of an
indexed register is added to the address part of the
instruction to obtain the effective address.
The indexed register may be a special register in CPU or
simply a register in register file.
In the application of array, the distance between the
beginning address and the address of the operand is the
index value stored in the register.

12. Stack instructions (push/pop)
 Reside in memory
 Due to the negative effects on performance,
a stack typically handles only state
information related to procedure
calls/returns/interrupts.
 A register holds the address for the stack is
called stack pointer (SP).