Machine Language in Computer Architecture

Machine Language in Computer Architecture – Machine language is a collection of binary digits or bits that the computer reads and interprets. It is also referred to as machine code or object code and is the only language a computer is capable of understanding.

Since computers are digital devices, they only recognize binary data. Every program video, image, and character of text is represented in binary. This binary data, or machine code, is processed as input by the CPU. The resulting output is sent to the operating system or an application, which displays the data visually. For example, the ASCII value for the letter “A” is 01000001 in machine code, but this data is displayed as “A” on the screen. An image may have thousands or even millions of binary values that determine the color of each pixel.

A machine language instruction has two parts. The first part is the operation code, which tells the computer what function to perform, and the second part is the operand, which tells the computer where to find or store the data that is to be manipulated. A programmer needs to write numeric codes for the instruction and storage location of data. The table below shows the computer instructions that are frequently used in a program.

Hexadecimal Symbol	Hexadecimal Code	Description
AND	0 or 8	AND M to AC
ADD	1 or 9	Add M to AC, carry to E
LDA	2 or A	Load AC from M
STA	3 or B	Store AC in M
BUN	4 or C	Branch unconditionally to m
BSA	5 or D	Save return address in m and branch to m + 1
ISZ	6 or E	Increment M and skip if zero
CLA	7800	Clear AC
CLE	7400	Clear E
CMA	7200	Complement AC
CME	7100	Complement E
CIR	7080	Circulate right E and AC
CIL	7040	Circulate left E and AC
INC	7020	Increment AC
SPA	7010	Skip if AC is positive
SNA	7008	Skip if AC is negative
SZA	7004	Skip if AC is zero
SZE	7002	Skip if E is zero
HLT	7001	Half computer
INP	F800	Input information and clear flag
OUT	F400	Output information and clear flag
SKI	F200	Skip if input flag is on
SKO	F100	Skip if output flag is on
ION	F080	Turn interrupt on
IOF	F040	Turn the interrupt on

A program written for a computer may be in one of the following categories:

1. Binary code: This is a sequence of instructions and operands in binary that list the exact representation of instructions as they appear in computer memory.
2. Octal or hexadecimal code: This is an equivalent translation of the binary code to octal or hexadecimal representation.
3. Symbolic code: The user employs symbols (letters, numerals, or special characters for the operation part, the address part, and other parts of the instruction code. Each symbolic instruction can be translated into one binary-coded instruction. This translation is done by a special program called an assembler. Because an assembler translates the symbols, this type of symbolic program is referred to as an assembly language program.
4. High-level programming languages: These are special languages developed to reflect the procedures used in the solution of a problem rather than be concerned with the computer hardware behavior. An example of a high-level programming language is Fortran. It employs problem-oriented symbols and formats. The program is written in a sequence of statements in a form that people prefer to think in when solving a problem. However, each statement must be translated into a sequence of binary instructions before the program can be executed in a computer. The program that translates a high-level language program to binary is called a compiler.

Now, using a basic computer to illustrate the relation between binary and assembly languages, consider a binary program to add two numbers.

Location	Instruction code	Instruction code	Instruction code	Instruction code
0	0010	0000	0000	0100
1	0001	0000	0000	0101
10	0011	0000	0000	0110
11	0111	0000	000	0001
100	0000	0000	0101	0011
101	1111	1111	1110	1001
110	0000	0000	0000	0000

The first column gives the memory location (in binary) of each instruction or operand. The second column lists the binary content of these memory locations. (The location is the address of the memory word where the instruction is stored. It is important to differentiate it from the address part of the instruction itself. The program can be stored in the indicated portion of memory, and then executed by the computer starting from address 0. The hardware of the computer will execute these instructions and perform the intended task.

Advantages of machine language:

• Machine language makes fast and efficient use of the computer.
• It requires no translator to translate the code. It is directly understood by the computer.

Disadvantages of machine language:

• It is machine-dependent, i.e., it differs from computer to computer.
• It is difficult to program and write.
• It is prone to errors.
• It is difficult to modify.