Also, user services recently told me (contrary to what I was told earlier) that if you go to one of the labs and copy the CBT icon on the desktop onto a floppy, then copy it from the floppy onto your computer in the residence halls, it should allow you to access the CBT modules from your room. If someone tries this and it works, please let me know.
2. Lab 3: Remember, you must complete Lab 3 (the CBT training modules for Windows 95) by class on Tuesday, September 15; credit for the lab will be based on your performance on an in-class quiz to be given at the beginning of the period. The 10-point quiz will consist entirely of questions taken from the test questions in the CBT modules. See the web page for the lab for more details.
Storage is binary. We talked about this in some detail. All computer memory is binary -- storage is accomplished by using lots and lots of things that can be in one of two states (e.g switches that can be on or off, circuits that can be open or closed, magnetized regions that can have one of two polarities, bits of a compact disk that can be either smooth or pitted). As we discussed in class, there's nothing necessary about this -- you could construct a digital computer around switches with three settings, or even, say, ten settings. Had we used ten-state devices, we would have gotten numbers expressible in decimal notation as nice round numbers. Since instead computers are based around two-state devices, we get instead numbers that are nice round numbers -- in binary notation! (E.g. 256 decimal, a rather unattractive, lumpy number, is 1 0000 0000 binary -- as nice and round a number as you could please!)
Bits and bytes. A bit (short for binary digit) is a unit of memory that can be in one of two states. As discussed in class, we can regard a bit as capable of distinguishing between two possible states of affairs, and telling us which obtains. Two bits (two on-off switches, say) enable us to represent twice as many possibilities, since with two switches we can represent off-off, off-on, on-off, and on-on -- four different combinations of states. In general, n bits will enable us to represent 2^n (by which I mean 2 to the nth power) different possibilities. So, for example, one byte is 8 bits, and is the amount of storage typically used to represent a character; since a byte is 8 bits, it can represent up to 2^8 (2 to the 8th power) = 256 possibilities.
Binary notation. Numbers, like everything else we might want to represent by states of the computer's memory, must be represented in the computer in binary. We can think of each digit of a binary number as representing the state of a single bit of memory. Just as single digits in decimal notation represent different amounts depending on their place, so binary digits also can be thought of as representing different amounts depending on where in the whole numeral they occur. We can express binary amounts in expanded notation just as we can decimal amounts. Thus, just as 256 decimal is (2 X 10^2) + (5 X 10^1) + (6 X 10^0) = (2 X 100) + (2 X 10) + (2 X 1), so we can represent, say, 101 binary as (1 X 2^2) + (0 X 2^1) + (1 X 2^0) = 4 + 0 + 1 = 5 (decimal).
Kinds of information. We distinguished between visual, audio, numeric, character, and instructional information. These are very different kinds of information. But if the computer is to be able to manipulate them, they must all be represented, at bottom, in binary terms. Since we've seen how to represent numeric information in binary terms, we can think of representing other kinds of information, such as visual information, as a matter of translating the information into a numeric form; since we know how numeric information can be stored in binary, we've then shown how to store the other kinds of information. We'll discuss how this translation from visual or audio (etc.) to numeric and thence to binary information is accomplished next week. We'll particularly stress the translation from character information to binary information, since we'll also be studying how to use a word-processing program.