In which decade of the twentieth century was the early form of the Internet first implemented as operational computer networks?

Introduction / Context:
This question tests knowledge about the history of computer networks and the origin of the Internet. The Internet did not appear suddenly in its modern form but grew out of earlier experimental networks. The first large scale operational packet switched network that is widely regarded as the ancestor of the modern Internet was called ARPANET and became functional in the late 1960s. Therefore, identifying the correct decade is essential for answering the question.

Given Data / Assumptions:

• The focus is on the decade when the early form of the Internet was first implemented.
• The options are the 1940s, 1960s, 1970s and 1980s.
• The question refers to computer networks that form the basis of today's Internet, not to theoretical ideas alone.
• Standard timelines used in computer history are assumed.

Concept / Approach:
The modern Internet grew from ARPANET, a network funded by the Advanced Research Projects Agency in the United States. ARPANET connected several research institutions and used packet switching technology. The first successful message on ARPANET was sent in 1969, which clearly places the initial implementation in the 1960s. Later decades saw important expansions and standardisation of protocols, but the earliest operational network dates back to the late 1960s. Thus, the correct decade is the 1960s.

Step-by-Step Solution:
Step 1: Recall that early computers were developed during the 1940s and 1950s, but large scale networking did not exist then. Step 2: Remember that ARPANET, the direct ancestor of the Internet, sent its first successful message in 1969. Step 3: Recognise that this year belongs to the 1960s decade. Step 4: Consider the 1970s and 1980s as decades when the network expanded and protocols like TCP and IP were developed and standardised. Step 5: Understand that the question is about first implementation, not later growth. Step 6: Conclude that the correct decade is the 1960s and select that option.

Verification / Alternative check:
One way to verify is to match key dates: ARPANET's first node connections and successful tests occurred in 1969. The term Internet and the broader interconnection of networks became more common by the late 1970s and early 1980s, but those developments built upon the initial 1960s work. Therefore, if the question asks for when the Internet was first implemented as networks, the safest answer is the 1960s.

Why Other Options Are Wrong:
The 1940s are too early, as computers themselves were just emerging and network infrastructure did not exist. The 1970s saw further development of networking protocols and international links, but this was after the initial implementation. The 1980s saw the spread of personal computers and more public access networks, again much later than the first experiments. Hence, these decades describe later stages in the Internet's evolution, not its earliest implementation.

Common Pitfalls:
Learners may confuse the decade when the word Internet became common in public usage with the decade when its technological foundation began. Some might also associate the Internet only with the widespread use of the World Wide Web from the 1990s, forgetting that the underlying network existed earlier. To avoid these errors, it is helpful to separate three phases in memory: ARPANET implementation in the 1960s, protocol standardisation and growth in the 1970s and 1980s, and web based popular access in the 1990s.

Final Answer:
The early form of the Internet was first implemented as operational computer networks in the 1960s.