Which register maintains the source index for various string operations?

Which register maintains the source index for various string operations?

• A. Extended Instruction Pointer (EIP)
• B. Extended Stack Pointer (ESP)
• C. Extended Base Pointer (EBP)
• D. Extended Source Index (ESI)

Answer: (D)

In string operations on x86, there are dedicated registers to track where data is read from and where it is written to. The source index holds the address of the data being read from, and the Extended Source Index is the register that serves this role in 32-bit mode. That means it points to the source memory location for instructions like movs, cmps, lods, and scas, with EDI serving the destination index for where data is written. The other registers mentioned have different roles: the instruction pointer controls the flow of execution, the stack pointer manages the call stack, and the base pointer is used for addressing stack frames. So the register that maintains the source index is the Extended Source Index.

In string operations on x86, there are dedicated registers to track where data is read from and where it is written to. The source index holds the address of the data being read from, and the Extended Source Index is the register that serves this role in 32-bit mode. That means it points to the source memory location for instructions like movs, cmps, lods, and scas, with EDI serving the destination index for where data is written. The other registers mentioned have different roles: the instruction pointer controls the flow of execution, the stack pointer manages the call stack, and the base pointer is used for addressing stack frames. So the register that maintains the source index is the Extended Source Index.