Identifying the register type from its behavior Which register accepts a complete binary number serially (one bit at a time) and also shifts stored bits out one at a time?

Introduction / Context:
Register classifications describe how data enters and leaves: serial or parallel, in and out. Matching behavioral descriptions to register types is basic digital logic literacy.

Given Data / Assumptions:

• Input arrives as a bitstream (serial).
• Output also departs as a bitstream (serial).
• No requirement for simultaneous multi-bit output.

Concept / Approach:

By definition, a serial-in, serial-out (SISO) register uses a single data line for input and typically exposes the last stage as the serial output. On each clock, data shifts one stage forward; after N clocks, an N-bit word has been fully entered or exited.

Step-by-Step Solution:

Verification / Alternative check:

Contrast with SIPO (serial-in, parallel-out), which would provide all bits at once; PISO (parallel-in, serial-out), which would load in parallel but shift out serially; PIPO, which does both in parallel.

Why Other Options Are Wrong:

• PIPO and PISO include parallel operation, contradicting the description.
• SIPO outputs in parallel, not one bit at a time.

Common Pitfalls:

• Confusing direction of data movement with width of the I/O interface.

Final Answer:

serial-in, serial-out