65 lines
2.6 KiB
Markdown
65 lines
2.6 KiB
Markdown
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---
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id: iqh8
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tags:
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- binary
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- CPU
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- hardware
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- computer-architecture
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created: Monday, March 11, 2024
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---
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# Machine code
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No matter how a program was originally written, it eventually needs to execute
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on a [[CPU_architecture|CPU]] as a series of machine language instructions.
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## Example machine instruction
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The following machine instruction is an instruction that would be understood by
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an [[Instruction_set_architectures| ARM ISA]]. It moves the number `4` into the
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`r7` register:
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```
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11100011101000000111000000000100
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```
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This 32-bit line of binary has a series of instructions embedded within it. We
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partition each part of the sequence below, from left to right, mapping it to the
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instruction:
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| Binary sequence | Instruction | Action |
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| --------------- | -------------------- | ---------------------------------------- |
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| 1110 | condition | always execute (unconditional) |
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| 00 | -- | -- |
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| 1 | immediate | value is in the last 8 bits |
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| 1101 | opcode | `mov` : move the value |
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| 0 | -- | -- |
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| 0000 | -- | -- |
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| 0111 | destination register | destination is 0111 which means `r7` |
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| 0000 | -- | -- |
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| 00000100 | immediate value | the binary representation of decimal '4' |
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- The blank zeros are also instructions, they are just not used in this
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instruction
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- The condition sequence tells us the instruction should run in all conditions
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not only under certain circumstances
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- The immediate bit (`1`) tells us whether the the value we are accessing is
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contained within the instruction or whether it is stored in a register. In
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this scenario `1` means the value is in the instruction. If it were `0`, the
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register where the value is located would be specified elsewhere in the
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instruction (in one of the currently blank sequences).
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- The opcode correspoons to `mov` the value.
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- THe destination register details where the value should be moved to (`r7`)
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- Finally, the immediate value is equivalent to decimal `4`
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## Difficulty
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Binary sequences are hard to understand, even if converted to the
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[[Hexadecimal_number_system]]. We have a better way of managing operations on
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the machine level: [assembly](Assembly.md)
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