How many computers made up the first Internet?

When ARPANET first ran in 1969 it consisted of 4 nodes, each consisting of an IMP minicomputer connected to one mainframes. The 4 nodes were at:

• SRI in CA with an SDS 940 mainframe
• UCLA in CA with a Sigma 7 mainframe
• UCSB in CA with an IBM 360/75 mainframe
• BYU in UT with a DEC PDP-10 mainframe

That makes a total of 8 computers (counting the IMPs).

The ARPANET was decommissioned in 1990 an became the internet.