Computers as Components, 2nd Edition

344 CHAPTER 6 Processes and Operating Systems

■ The compression and decompression modules run at the same rate as the

speaker and telephone I/O modules, but they are not directly connected to

devices. We will therefore call them as subroutines to the interrupt modules.

One subtlety is that we must construct a very simple file system for messages,

since we have a variable number of messages of variable lengths. Since messages

vary in length, we must record the length of each one. In this simple specifica-

tion, because we always play back the messages in the order in which they were

recorded, we don’t have to keep a full-fledged directory. If we allowed ...