Dear Ulla. About the ARPANET, one node a month were brought up each month in late 1969. Each site had an IMP. The 4 IMPS formed the communications subnetwork. To each IMP was attached a host. These hosts were time sharing systems. Therefore the number of terminals or even computers connected via the 4 node ARPANET was more than 4. The history of the ARPANET and timesharing can be seen in chapters 6, 7 and 8 of "Netizens: On the History and Impact of Usenet and the Internet by Michael Hauben and ronda Hauben". An online version is at: http://www.columbia.edu/~rh120 The hard cover edition was published by the IEEE Computer Science Press in 1997. On August 30, 1969, the first IMP arrived at the University of California, Los Angeles (UCLA) which was to be the first site of the new network. It was connected to the SDS Sigma 7 computer at UCLA using the GENIE operating system. Shortly thereafter IMPs were delivered to the other three sites in this initial testbed network. At Stanford Research Institute (SRI), the IMP was connected to an SDS-940 computer using the SEX operating system. At the University of California, Santa Barbara (UCSB), the IMP was connected to an IBM 360/75 using OS/MTV. And at the University of Utah (Utah), the fourth site, the IMP was connected to a DEC PDP-10 using the TENEX operating system. By the end of 1969, the first four IMPs had been connected to the host computers at their individual sites and the network connections between the IMPs were operational. The researchers and scientists involved could begin to identify the problems they had to solve to develop a working network where there would be communication from host to host. The first sites of the ARPANET were picked to provide either network support services or unique resources. The key services the first four sites provided were(24): UCLA - Network Measurement Center SRI - Network Information Center UCSB - Culler-Fried interactive mathematics UTAH - graphics (hidden line removal) A much cited version of The Untold History of the ARPANET is http://www.dei.isep.ipp.pt/docs/arpa.html)