Do you remember Tymnet? If you don't remember, are too young to remember, or fondly remember, this book is for you.This is the story of the worldwide network of online services that existed long before the Internet. Before the modern "Cloud" there was time-sharing. The earliest computers were very expensive, single-task machines devoted to running a single program at a time. Each program loaded from a stack of punch cards, and ran its course without interacting with the outside world. Running payroll, for example, meant that the system was unavailable for any other function until the payroll was complete, the checks printed, the books balanced, and updates written to new punch cards and stored for the next run. This very expensive machine spent most of the time waiting on the peripherals, the printer, the card reader, and the card punch. We called this "Batch Processing." Multitasking was a brilliant innovation, allowing multiple programs to run simultaneously, sharing the expensive computing resources across multiple simultaneous batch jobs. Interactive time-sharing soon followed, allowing multiple users to interact with the computer in real time using electro-mechanical Teletype terminals. Then came networks. We know of ARPANET, but have forgotten the others. Several companies arose to offer "cloud-based" applications available remotely using mechanical terminals, a time-shared computer, and a network. One such company was Tymshare, and the network Tymshare created to deliver remote computer services was Tymnet. Tymnet began operations in late 1968 using a stylized cloud logo that claimed the first "Cloud" services-precursors to today's pervasive cloud infrastructure. Time-sharing thus became the first layer of virtualization, and the foundation upon which we built additional layers. Today's sophisticated container-based virtual services ride upon a time-shared foundation. Teletypes quickly gave way to electronic terminals, and speeds increased rapidly from the 110 bps of the mechanical terminals. In 1972, Tymnet began offering remote, "cloud-based" applications to companies and institutions world-wide, marking the first truly commercial network. Today's cloud, of course, is far more extensive and varies in the way it allocates virtualized resources among consumers, but the underlying principle is unchanged. We run applications on remote computers and share the physical resources with many others.