Transistor
A transistor is the most basic building block of a computer.
It simply consists of the equivalent of three wires:
a thin wire, and two thicker wires.
The thin wire controls whether the thicker wires
pass electricity to each other.
If a small amount of electricity is present
in the thin wire, then a larger amount of electricity
is allowed to pass through the larger wires
(the larger wires are connected).
But if no electricity is present in the
thin wire, the larger wires are disconnected
from each other (no electricity flows between them).
Thus a transistor is essentially a tiny
electrically-operated switch.
Instead of using wires, it actually uses
semiconductor materials.
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“Each individual transistor functions like a
miniature switch that can be operated electrically.” [ 1 ]
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Transistors are organized into “logic gates,”
which are in turn organized to add and combine bits, which
is organized to subtract, multiply, divide, etc.
Anything that is done on computers simply comes down to
the logic of transistors working together.
We will now examine the use of a single transistor in
accessing a bit of dynamic random access memory (DRAM).
Each bit is stored in a single capacitor which is accessed
(switched) by a single transistor that is called a
pass transistor (it lets electricity pass to or from
the capacitor).
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“The pass transistor acts like a switch: when the signal
on the word line is asserted, the switch is closed,
connecting the capacitor to the bit line.” [ 2 ]
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1.
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Douglas E. Comer,
Essentials of Computer Architecture
(Pearson, 2005),
p. 53, 100.
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2.
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David A. Patterson and John L. Hennessy,
Computer Organization and
Design: The Hardware/Software Interface
3rd Ed.,
p. B-63
(and
2nd Ed.,
p. B-32).
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