Shift registers — which type can shift left or right? Fill in the blank: A _________ shift register can shift stored data either left or right under control, enabling bidirectional bit movement.

Introduction / Context:
Shift registers are versatile building blocks. Some can shift in one direction only, while others support both left and right shifts. Recognizing which name corresponds to bidirectional capability helps when designing arithmetic shifters, serial interfaces, or data alignment logic.

Given Data / Assumptions:

• Shift operation is clocked and direction-controlled.
• Register supports moving bits either toward MSB (left) or toward LSB (right).
• Parallel load may or may not be provided, depending on the specific device.

Concept / Approach:
A register that supports both directions is commonly called a “bidirectional shift register.” Some parts are called “universal shift registers,” which add parallel load and often three modes (shift left, shift right, parallel load). However, the minimal correct fill-in for left/right capability alone is “bidirectional.”

Step-by-Step Solution:

Verification / Alternative check:
Datasheets for 74HC194/195 list modes including shift left/right and parallel load; literature commonly calls devices with two-direction shifting “bidirectional,” and those plus parallel load “universal.”

Why Other Options Are Wrong:

• tri-state: Describes output enable behavior, not shift direction capability.
• universal: Often correct for parts that add parallel load, but the most direct fill-in for left/right shifting alone is “bidirectional.”
• bidirectional universal: Redundant phrasing not used as a standard category.
• ring: A different structure that circulates a single 1 or 0; not general left/right shifting.

Common Pitfalls:
Assuming “universal” is required terminology for any bidirectional register; overlooking that some devices offer only one shift direction.

Final Answer:
bidirectional