Identify the first widely used integrated logic family in early monolithic IC history (preceding DTL and TTL).

Introduction / Context:
The evolution of digital logic families traces the development of integrated circuits from simple, low-density gates to today's high-performance CMOS. Recognizing which family appeared first helps contextualize trade-offs in speed, power, and integration levels across generations of technology.

Given Data / Assumptions:

• We refer to early monolithic integrated logic used in the 1960s era.
• Options include RTL (resistor–transistor logic), DTL (diode–transistor logic), TTL (transistor–transistor logic), and MOS (metal–oxide–semiconductor).
• The question asks for the earliest among the commonly cited integrated families.

Concept / Approach:
Resistor–transistor logic (RTL) emerged first in monolithic IC form and offered simple inverter and gate structures using resistors for input networks and a single transistor for switching. DTL followed with improved noise margins using diodes in the input networks. TTL later became dominant in the late 1960s and 1970s because of better speed and fanout. MOS logic matured subsequently and ultimately led to CMOS dominance due to extremely low static power and high integration density.

Step-by-Step Solution:
Order the families historically: RTL → DTL → TTL → MOS/CMOS (widespread later).Select the earliest widely used integrated family: RTL.Confirm that the others either came later or became dominant later.Choose “RTL.”

Verification / Alternative check:
Historical accounts of early ICs from Fairchild and other pioneers describe RTL as the first integrated logic family in production, with DTL and TTL improving on speed and noise margin thereafter.

Why Other Options Are Wrong:
DTL and TTL post-date RTL in integrated form; MOS became significant later with PMOS/NMOS and then CMOS processes. “None of the above” is incorrect because RTL is the correct earliest family.

Common Pitfalls:
Confusing discrete-circuit inventions with integrated versions; assuming TTL came first due to its later popularity; overlooking that CMOS dominance is modern and not the earliest in IC history.

Final Answer:
RTL