May 2017

SECTION III-4: CPU, RAM and ROM in Computers

For the CPU to process information, the data must be stored in RAM or ROM. The function of ROM in computers is to provide information that is fixed and permanent.

SECTION III-3: Data Bus and Address Bus in Computers

The address bus is used to identify the devices and memory connected to the CPU, the more address buses available, the larger the number of devices that can be addressed. The number of address buses for a CPU determines the number of locations with which it can communicate. The number of locations is always equal to 2x, where x is the number of address lines, regardless of the size of the data bus.

SECTION III-2: Internal Organization of Computers

The internal working of every computer can be broken down into three parts:

  • CPU (Central Processing Unit)
  • Menory
  • I/O (Input / Output) devices




The concept that will be discussed, applicable to all computers, including the IBM PC, PS/2, and compatibles. One of the most important features of a computer is how much memory is has. Bit is a binary digit that can have the value 0 or 1. A Byte is defined as 8 bits. A nibble is a half byte, or 4 bits. A word is two bytes, or 16 bits. The display is intended to show the relative size of these units, they could all be composed of any combination is zeros and ones.

SECTION II-3: Decoders and Flip-Flop Application of Logic Gates


Decoders are widely used for address decoding in computer design. Demonstrated below decoders for 9 (1001 binary) and 5 (0101) using inverters and AND gates.


SECTION II-2: Logic Design Using Gates

If we add two binary digits there are four possible outcomes:

SECTION II-1: DIGITAL SYSTEM - Binary Logic and Logic Gates

Binary Logic:

Computers use the binary number system because the two voltage levels can be represented as the two digits 0 and 1. Signals in digital electronics have two distinct voltage levels. A system may define 0V as logic '0' and +5V as logic '1'. Picture below demonstrated this system with built-in tolerances for variations in the voltage.

SECTION I-12: ASCII - American Standard Code for Information Interchange

All information in the computer must be represented by 0's and 1's, binary patterns must be assigned to letters and other characters. In the 1960's a standard representation called ASCII was established. The ASCII code assigns Binary patterns for numbers 0 to 9, all the letters of the English alphabet, both upper-case capital and lower case, and many control codes and punctuation marks. The advantage of this system i s that it is used by most computers, so that information can be shared among computers.

SECTION I-11: Addition and Subtraction of Hex Numbers

By studying issues related to software and hardware of computers, it is often necessary to add or subtract hex numbers. Hex addition and subtraction is explained and demonstrated below.

Addition of Hex Numbers:

SECTION I-10: 2's Complement of Binary Number

To get the 2's complement of a Binary number, invert all the bits and then add 1 to the result. Inverting the bits is simply a matter of changing all 0's to 1's and 1's to 0's. This is called the 1's complement. Example is demonstrated below.


SECTION I-9: Addition of Binary and Hex Numbers

The Addition of Binary is a very straightforward process as demonstrated below showing the addition of two bits.

SECTION I-8: Counting in Bases 10, 2, and 16

Table Below demonstrated the relationship between all three Bases. Showed the sequence of numbers from 0 to 31 in decimal, along with the equivalent Binary and Hex numbers. In each base that when one more is added to the the highest digit, that digit becomes zero and a 1 is carried to the next-highest digit position. In decimal, 9 + 1 = 0 with a carry to the next-highest position. In Binary, 1 + 1 = 0 with a carry; similarly, in Hex, F + 1 = 0 with a carry.


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