In describing messages used in most message passing systems, it was observed that header information was usually fixed-length but the data in the message (often called the payload) was usually variable length. What makes this a very efficient way to handle messages, i. e., why is it efficient for headers to be fixed length and payloads to be variable length?

In 1973 was when graphical user interfaces (guis) pioneered.

I’d say platform as a service (paas) or application platform as a service (apaas) or platform base service is a category of cloud computing services that provides a platform allowing customers to develop, run, and manage applications without the complexity of building and maintaining the infrastructure typically associated with developing and launching an app.

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In computer or look in the wikipedia