Why is a digital wristwatch called "digital?"
Because it shows time using definite digits, rather than positions of hands that have to be measured. (It would be less correct to say "because it has a computer inside.")
Which of the following is a binary device:
The ignition switch of an automobile.
The hour hand of a clock.
A button on a hand calculator.
The volume control on a stereo.
- The ignition switch of an automobile. No
- The hour hand of a clock. No
- A button on a hand calculator. Yes
- The volume control on a stereo. No
Which is easier to build:
An on/off switch.
A light dimmer.
An on/off switch.
Which of the following methods for producing books is simple and easy?
Each book is individually made by scratching marks onto tablets of wet clay.
Each book is individually made by copying the characters onto paper with pen and ink.
Many copies of the book are made by carving flat wooden blocks with the text then printing the text on paper.
Many copies of the book are made by setting movable type and printing the text on paper.
Which is easier to do: (a) determine exactly how bright a light is, or (b) decide if it is on or off?
On or Off.
Why can a Chinese abacus be regarded as a "digital computer."
The computation is done by moving beads into definite positions. A bead is either placed where it counts as part of a number, or it is placed where it does not count. This "all or nothing" operation means that an abacus is a discrete device.
At time "T2", is the signal "on" or "off"?
The analog signal (continuously changing voltage signal) moves up and down, but at time "T2" it is clear that it is above the threshold. Exact measurement is not needed.
Is is clear that the signal is "off" at time T1 and "on" at time T2?
If the signal were regarded as an analog signal, and exact values were important, would some information present in the first signal (before the noise) have been lost?
Yes—if the signals represented a singer's voice, the noisy signal would sound, er.. well... noisy. After just one copy, information has been lost.
Something might be wrong here. Is the signal is "on" or "off" at the time "x"? This is not easy to tell. What is worse, a different amount of noise changes the answer. What can be done about this problem? (Hint: must the value of the signal be known at all times?)
The system is built so that the signal is tested only at particular times, and that changes in the signal occur between these times.
Which is faster, a 400 MHz Pentium processor or a 800 MHz Pentium processor?
The 800 MHz processor, since it checks values 800 million times per second (twice as many as the 400 MHz processor).
(However, if the processors are different types there are other factors besides clock speed that determine how much each processor can do in a second.)
Can charaters from alphabets other than English be represented?
Of course. Any type of symbol at all can be assigned a binary pattern to represent it.
Can printed music be represented using binary?
Sure — any symbols can. There are "music processor" programs for printed music that work like word processor programs for printed text.
Sometimes people say, "All that a computer can handle is numbers. It doesn't understand anything else." Do you think that this is correct?
No. Any type of symbolic data can be represented using binary, not just numbers. At the electronic level, everything is a binary pattern (which some people call a "number"), so the statement is sort-of correct.