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Innovation within services like CompuServe took place at the center of the network rather than at its fringes. PCs were to be only the delivery vehicles for data sent to customers, and users were not themselves expected to program or to be able to receive services from anyone other than their central service provider. CompuServe depended on the phone network’s physical layer generativity to get the last mile to a subscriber’s house, but CompuServe as a service was not open to third-party tinkering.
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Jonathan L. Zittrain (The Future of the Internet: And How to Stop It)