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the requirement for extra bits of word length. If we add two 8-bit numbers together,
we may well need a 9-bit number to store the result! Stepping up to the next largest
word length computer is often a safe bet; a 16-bit computer might be needed.
Computer horsepower Even a tiny 4-bit computer can perform all the calcula-
tions required in a robot control system. The real question is, can such a 4-bit com-
puter do it fast enough to keep up with the requirements of the robot? If we design
the robot very carefully, we can minimize the requirement for a lot of computer
horsepower. We can go into how to do that in a later chapter of this book. The point
is, if we’re sizing the computer to the task at hand, we can gain a lot by minimiz-
ing the task. Then we only have to pick a computer large enough to do the job.
Memory size Often, the word width of the computer dictates the word width of
the memory bank. A 32-bit computer works best with a 32-bit-wide memory mod-
ule. As such, the word length can also affect the size and cost of the memory.

POWER

Many robots are battery powered. We’ll tackle power considerations later but should
mention it here. To save power, look for the following features in a computer:
Lower-voltage electronics
Low-power operation
Support in the operating software for low-power states
Lower-frequency operation (if we can stand the slower operation)

MEMORY SUPPORT CIRCUITRY

Computers require memory to store their programs and data. The memory can be
attached to the computer in several different ways. This section outlines some of those
options.

Stored program Many questions have been asked about the program software
itself. Where will it be stored? Flash memory and disk are two popular methods.
Flash memory is more reliable physically, which is important if the robot will be
mobile. We’ll look at both types of memory shortly.
Also, how will the program be changed? It’s always a good idea to maintain the
ability to upgrade the software in the robot. That means we need a method of get-
ting the program information into the robot.
This can be done in a number of ways, including through a communication chan-
nel. If the robot has a communication channel to the outside world, we can encode