The personal computer is assuming the role of a client in this network model scenario.
The personal computer in this scenario is assuming the role of a client.
In a network model, a client refers to a device (such as a personal computer) that requests services or resources from a server. In this case, the author's personal computer is requesting to upload a chapter document to the file server of the book publisher.
Unlike a server, which provides services or resources to other devices, the personal computer is acting as a client by making a request.