CSCI 1300 - Lecture Notes

CSCI 1300
Lecture Notes

9/23/97

Administrative Stuff

I will be at a conference from 9/24 - 10/1. Prof. Karl Winklmann will teach the class in my place.

Results of programming assignment #2

Results of Quiz #1.

Quiz #2 - Tuesday Oct. 7

Programming assignment #5 due Oct. 3

Programming assignment #6 due Oct. 10

Memory Organization

Physical memory

The hardware elements that are used for almost all computer memory have exactly two states - low voltage and high voltage.

Each element of memory is used to represent one binary digit of information, called a bit.

We say that the low state represents the value 0 and the high state represents the value 1.

The bits are organized physically into words. The number of bits in a word is dependent upon the details of the hardware, but is usually 16 or 32.

Physical memory is essentially one big list of words. The address of a particular memory location is just it's position in the list.

Words are broken into 8 bit logical elements called bytes.

Number systems

Decimal numbers - base 10

Decimal numbers use 10 digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)

The position of a digit in a number indicates the power of 10 that it is multiplied by.

Example:

125 = (1 * 100) + (2 * 10) + (5 * 1)

but 100 is 10^2, 10 is 10^1, and 1 is 10^0

So 125 = (1 * 10^2) + (2*10^1) + (5 * 10^0)

Note that this is the same as ((((1 * 10) + 2) * 10) + 5)

Binary numbers - base 2

Binary numbers work the same way as decimal numbers, but have only two digits (0 and 1).

Binary numbers are a natural representation for computers because of the two-state memory elements.

Example:

>p>

10b = (1 * 2^1) + (0 * 2^0) = 2 + 0 = 2

1101b = (1 * 2^3) + (1 * 2^2) + (0 * 2^1) + (1 * 2^0) = 8 + 4 + 0 + 1 = 13

Equivalent to ((((((1 * 2) + 1) * 2) + 0) * 2) + 1)

Adding binary numbers: 01001011 + 10001101 = 11011000

How many bits does it take to store this number?

Hexadecimal numbers - base 16

Hexadecimal numbers use 16 digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F)

Natural for computers since 4 bits = one hex digit

Example:

4A7h = (4 * 16^2) + (10 * 16^1) + (7 * 16^0) = 1024 + 160 + 7 = 1191

Equivalent to ((((4 * 16) + 10) * 16) + 7)

Adding hex numbers: 4A7 + BE0 = 1087h = 4231d

How many bits does it take to store this number?

Octal numbers - base 8

Octal numbers use 8 digits (0, 1, 2, 3, 4, 5, 6, 7, 8)

3 bits = one octal digit

Example:

235o = (2 * 8^2) + (3 * 8^1) + (5 * 8^0) = 128 + 24 + 5 = 157

How many bits does it take to store this number?

Data Storage

Computer memory is all bits.

In our systems, each word is 32 bits long

That means that in one word we can store any number between 0 and 2^32 - 1 = 4294967295

Bit operations: shifting, masking

In Borland C++,