The hardware - The Computing Universe: A Journey through a Revolution - page 23

2 The hardware

I always loved that word, Boolean.
Claude Shannon 1

Going through the layers

In the last chapter, we saw that it was possible to logically separate the
design of the actual computer hardware - the electromagnetic relays, vacuum
tubes, or transistors - from the software - the instructions that are executed
by the hardware. Because of this key abstraction, we can either go down into
the hardware layers and see how the basic arithmetic and logical operations
are carried out by the hardware, or go up into the software levels and focus
on how we tell the computer to perform complex tasks. Computer architect
Danny Hillis says:

This hierarchical structure of abstraction is our most important tool in
understanding complex systems because it lets us focus on a single aspect of a
problem at a time. 2

We will also see the importance of “functional abstraction”:

Naming the two signals in computer logic 0 and 1 is an example of functional
abstraction. It lets us manipulate information without worrying about
the details of its underlying representation. Once we figure out how to
accomplish a given function, we can put the mechanism inside a “black box,”
or a “building block” and stop thinking about it. The function embodied by
the building block can be used over and over, without reference to the details
of what's inside. 3

Processor Memory I/O

In this chapter, like Strata Smith going down the mines, we'll travel downward
through the hardware layers ( Fig. 2.1 ) and see these principles in action.

Registers and logic circuits

Logic gates

George Boole and Claude Shannon

Electrons

In the spring of 1936, Vannevar Bush was looking for a smart electrical
engineering graduate who could assist visiting scientists in setting up their
calculations on his Differential Analyzer at MIT. Claude Shannon ( B.2.1 ), a

Fig. 2.1. A diagram showing the
major abstraction layers of computer
hardware.

23