Machine code is a low-level programming language that is directly executable by the central processing unit (CPU) of a computer.
If we open an executable program, we will see a bunch of data like the following, but with many, many (many!) more lines.
00 F3 0F 6F 05 D7 8E 06 00 0F 11 74 24 60 0F 11 44 24 70 41 80 FD 03 0F 84
9B 03 00 00 8B 7E 04 45 31 F6 85 FF 0F 89 AF FD FF FF 80 7E 08 00 0F 84 DB
02 00 00 31 FF 41 80 FD 01 40 0F 94 C7 83 C7 06 E9 AD FD FF FF 66 0F 1F 84
00 00 00 00 00 80 7C 24 6F 01 0F 84 3D 04 00 00 8B 44 24 60 48 83 F8 03 0F
86 5A 02 00 00 BA 03 00 00 00 E9 0E FF FF FF 0F 1F 44 00 00 40 84 ED 48 8D
3D 43 84 06 00 48 8D 05 40 84 06 00 48 0F 45 F8 E9 C8 FE FF FF 66 0F 1F 44
00 00 45 84 F6 0F 84 17 03 00 00 45 0F B6 F6 48 8D 05 BC 83 06 00 48 C7 44
24 70 01 00 00 00 41 BD 01 00 00 00 42 0F B6 04 30 88 84 24 80 00 00 00 48
8D 44 24 50 48 89 44 24 30 66 0F EF F6 C6 44 24 50 25 44 8B 76 04 48 8D 54
24 51 F3 0F 5A F1 40 84 FF 74 0A C6 44 24 51 23 48 8D 54 24 52 45 85 F6 78
0F 0F B7 05 12 8E 06 00 48 83 C2 02 66 89 42 FE 40 80 FD 01 C6 42 01 00 BF
F4 01 00 00 4C 89 FB 19 C0 83 E0 20 83 C0 41 88 02 49 8D 45 01 48 89 44 24
38 0F 1F 00 4C 29 EF 4A 8D 0C 2B 48 89 FD 45 85 F6 0F 88 A4 00 00 00 4C 8B
44 24 30 F2 0F 11 74 24 20 45 89 F1 48 89 FA E8 17 F4 FE FF 48 8B 7C 24 78
48 8B 5C 24 68 85 C0 0F 88 A4 00 00 00 48 98 48 39 E8 0F 82 EA 00 00 00 48
8B 54 24 38 48 01 D0 48 39 C7 73 AD 48 89 FD 48 D1 ED 48 01 FD 48 39 C5 48
(... many many more lines)What is that? That is machine code, that is, the binary code necessary for your processor to execute the program. This is the only language your processor understands.
Each instruction corresponds to a specific basic operation that the CPU can execute. For example, adding two numbers, transferring data from one place to another in memory, or comparing two numbers. Very basic and simple operations.
The available instructions vary between architectures and processor models. An old x86 8088 had 81 instructions. A modern processor can have several hundred instructions available.
Machine code uses the elementary instructions by calling them by their “operation code” (opcode). Which is simply a numerical representation that we give to each instruction.
As we can see, machine code is completely dependent on the underlying hardware. Each processor has its own set of instructions, opcodes, and its own register structure.
This means that machine code written for a specific processor architecture is not directly compatible with another different processor. That pile of bytes will only work on one type of processor.
Another obvious characteristic of machine code is that its readability is low. Because it is written in a sequence of zeros and ones, it is very difficult for humans to understand and maintain. In addition, machine code lacks abstractions and advanced control structures found in high-level programming languages.
Believe it or not, at the beginning of programming it was programmed like this. And as you can imagine, it was a hell to program in that. It was a very slow, complicated process, and prone to errors. That’s why other languages soon emerged, such as assembler, which made the process simpler.
Although machine code is considered (and is) a low-level programming language, its direct use in the development of modern applications is very limited. Not to say practically nonexistent.
Currently, most programmers use high-level programming languages, such as C++ or Python, which offer abstractions and control structures that are more friendly for software development.