Information Technology Reference
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3
The software is in the holes
Computer programs are the most complicated
things that humans have ever created.
Donald Knuth
1
Software and hardware
Butler Lampson, recipient of the Turing Award for his contributions to
computer science, relates the followi ng anecdote about software:
There's a story about some people who were writing the software for an early
avionics computer. One day they get a visit from the weight control officer,
who is responsible for the total weight of the plane.
“You're building software?”
“Yes.”
“How much does it weigh?”
“It doesn't weigh anything.”
“Come on, you can't fool me. They all say that.”
“No, it really doesn't weigh anything.”
After half an hour of back and forth he gives it up. But two days later he
comes back and says, “I've got you guys pinned to the wall. I came in last
night, and the janitor showed me where you keep your software.”
He opens a closet door, and there are boxes and boxes of punch cards.
“You can't tell me those don't weigh anything!”
After a short pause, they explain to him, very gently, that the software is in
the holes.
2
It is amazing how these holes (
Fig. 3.1
) have become a multibillion-dollar busi-
ness and arguably one of the main driving forces of modern civilization.
In the previous chapter we described the idea of separating the physical
hardware from the software. Identifying these two entities is one of the key
concepts of computer science. This is why we were able to go “down” into the
hardware layers and see how the arithmetic and logical operations could be
implemented without worrying about the software. Now let's go “up” into the
software levels and find out how to tell the computer what to do. Software, also
called a
program
, is a sequence of instructions which “give orders” to the hard-
ware to carry out a specific task. In this program we can use only the operations
Fig. 3.1. Carving holes on a punch
card. The software in the early days of
computing was represented by these
holes but the cards were actually
punched by machines.
39
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