Registers
Discover what registers are, why they are critical for performance, and how CPUs use them to store and process data quickly. We'll explore general-purpose and special-purpose registers across different architectures.
Let's start with the first component of assembly languages, registers.
Registers are few, very small but extremely fast pieces of memory inside a CPU.
They are usually (depending on the CPU) between 8 and 32 in total, and can hold very few bits (depends on the CPU, but usually 32-bit CPUs have 32-bit registers, etc...), but they are very fast to access as they are physically inside the CPU itself — unlike memory, which is further away and slower to access.
Each register has a name that identifies it.
For example, in M68K there are registers: d0, d1, ..., d7, a0, a1, ..., a7.
General Purpose Registers
These are the most common type of registers and can be used for a wide variety of tasks, like storing data, addresses, etc... Some architectures split this category further into:
- Data registers – they contain numeric data, like numbers, characters, etc...
- Address registers – they contain addresses and are used by instructions that indirectly access memory
- Floating point – they contain floating point numbers
- etc...
Special Purpose Registers
They are special registers usually managed by the CPU itself and used for specific purposes, there will be a more in depth explaination in future lectures.