Part 3: Writing about figure 1.2, the textbook author says, "Note that the exact nature of the channel is not important for this discussion." Explain why not. In another paragraph, explain what this has to do with abstraction.

Part 4: Consider a file stored on the computer you regularly use. List the hardware involved with storing and retrieving the file. Similarly, list the software. Is there data involved, other than the contents of the file itself? If so, what? If not, why is other data not needed? Could the contents of the file be something other than data? If so, what? If not, why not?

10 PART ONE AN OVERVIEW OF COMPUTER SYSTEMS FIGURE 1.2 Typical Web Browser Application Use Web Browser Web Server User Page request message Page request message Communication Channel URL HTML file HTML variety of forms, provided that the interface requirements are met, and are determined by such characteristics as performance, convenience, and cost. The work performed by an individual computer system within the IT system can be characterized by input, processing, and output. This characterization is often represented by the Input-Process-Output (IPO) model shown in Figure 1.3 Storage is also represented within this model. Alternatively, storage can be interpreted as output to be saved for use as future input. Storage is also used to hold the software programs that determine the processing operations to be performed. The ability to store programs and data on a temporary, short-term, or long-term basis is fundamental to the system. In Chapter 2, Section 2.2, we will show that all IT systems can ultimately be characterized by the same basic IPO model at all levels, from a single computer to a complex aggregation of computers, although the complexity of large systems may obscure the model and make it more difficult to determine the actual inputs, outputs, and processing FIGURE 1.3 A Computer Process Storage Input Process Output