In programming, processing data requires variables. You can simply think of registers as variables in assembly language. However, not all registers are treated as plain variables, but rather, each register has a designated purpose. The registers are categorized as being one of the following:

  • General purpose registers
  • Segment registers
  • Flag registers
  • Instruction pointers

In x86 architecture, each general purpose register has its designated purpose and is stored at WORD size, or 16 bits, as follows:

  • Accumulator (AX)
  • Counter (CX)
  • Data (DX)
  • Base (BX)
  • Stack pointer (SP)
  • Base pointer (BP)
  • Source index (SI)
  • Destination index (DI)

For registers AX, BX, CX, and DX, the least and most significant bytes can be accessed by smaller registers. ...

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