Chapter 10. IO

Chapter 10. I/O

On two occasions I have been asked [by members
of Parliament], "Pray, Mr. Babbage, if you put into
the machine wrong figures, will
the right answers come out?"
I am not able rightly to apprehend the kind of
confusion of ideas that could provoke such a question.
Charles Babbage

Input and output are critical in any design, because they mediate the interface of an application or library. To most users of your software, what your I/O components do is their entire experience of what the software is. So good I/O practices are essential to usability.

I/O operations are also particularly susceptible to inefficiencies, especially on large data sets. I/O is frequently the bottleneck in a system, and usually doesn't scale well. So good I/O practices are essential to performance too.

Yet another concern is that I/O deals with the software's external environment, which is typically less reliable than its own internals. Dealing successfully with the multiple failure modes of operating systems, filesystems, network connections, and human beings requires careful and conservative programming. So good I/O practices are essential to robustness as well.