ARPANET
ARPANET was the first operational Packet Switching network, developed in the late 1960s by the United States Department of Defense's Advanced Research Projects Agency (ARPA). It was designed to facilitate communication between different computer systems at various research institutions and was the precursor to the modern-day Internet. The network was initially intended to connect four nodes: the University of California, Los Angeles (UCLA), the Stanford Research Institute (SRI), the University of California, Santa Barbara (UCSB), and the University of Utah. ARPANET used TCP/IP protocol, which was developed by Vint Cerf and Bob Kahn, to enable communication between different networks. The success of ARPANET led to the development of other networks, such as NSFNET, which eventually merged to form the modern Internet.