Binary signal in computer registers for a given application
A subroutine call not only branches but saves the preceding contents of the PC somewhere. A return retrieves the saved contents of the PC and places it back in the PC, resuming sequential execution with the instruction following the subroutine call.
In a typical central processing unit CPU , the PC is a digital counter which is the origin of the term "program counter" that may be one of many registers in the CPU hardware. The instruction cycle  begins with a fetch , in which the CPU places the value of the PC on the address bus to send it to the memory. The memory responds by sending the contents of that memory location on the data bus. This is the stored-program computer model, in which executable instructions are stored alongside ordinary data in memory, and handled identically by it .
Following the fetch, the CPU proceeds to execution , taking some action based on the memory contents that it obtained. At some point in this cycle, the PC will be modified so that the next instruction executed is a different one typically, incremented so that the next instruction is the one starting at the memory address immediately following the last memory location of the current instruction. Like other processor registers, the PC may be a bank of binary latches, each one representing one bit of the value of the PC.
To identify the current instruction, the PC may be combined with other registers that identify a segment or page. This approach permits a PC with fewer bits by assuming that most memory units of interest are within the current vicinity. Use of a PC that normally increments assumes that what a computer does is execute a usually linear sequence of instructions. Take example of a CD-ROM, if the shiny surface is placed under a powerful microscope, the surface is observed to have very tiny holes called pits.
The areas that do not have pits are called land. Consists of eight digits ranging from Hexadecimal number system This is a base 16 number system that consists of sixteen digits ranging from and letters A-F where A is equivalent to 10,B to 11 up to F which is equivalent to 15 in base ten system.
The place value of hexadecimal numbers goes up in factors of sixteen. When converting a real number from binary to decimal, work out the integral part and the fractional parts separately then combine them.
Working from left to the right, each octal number is represented using three digits and then combined we get the final binary equivalent. The binary equivalent of the fractional part is extracted from the products by reading the respective integral digits from the top downwards as shown by the arrow next pag. To convert binary numbers to their binary equivalents, simply group the digits of the binary number into groups of four from right to left e.
The next step is to write the hexadecimal equivalent of each group e. The simplest method of converting a hexadecimal number to binary is to express each hexadecimal digit as a four bit binary digit number and then arranging the group according to their corresponding positions as shown in example. The main purpose of using ones compliment in computers is to perform binary subtraction.
For example to get the difference in 5 — 3, using the ones compliment, we proceed as follows:. Like in ones compliment, the twos compliment of a number is obtained by negating a positive number to is negative counterpart.
For example to get the difference in , using twos compliment, we proceed as follow:. Computers are classified according to functionality, physical size and purpose. Functionality, Computers could be analog, digital or hybrid. Digital computers process data that is in discrete form whereas analog computers process data that is continuous in nature. Hybrid computers on the other hand can process data that is both discrete and continuous. In digital computers, the user input is first converted and transmitted as electrical pulses that can be represented by two unique states ON and OFF.
Although the two graphs look different in their appearance, notice that they repeat themselves at equal time intervals. Electrical signals or waveforms of this nature are said to be periodic. Generally,a periodic wave representing a signal can be described using the following parameters Amplitude A Frequency f periodic time T Amplitude A: It is measured in hertz. When a digital signal is to be sent over analog telephone lines e.
This is done by connecting a device called a modem to the digital computer. This process of converting a digital signal to an analog signal is known as modulation.
On the receiving end, the incoming analog signal is converted back to digital form in a process known as demodulation. Data and instructions cannot be entered and processed directly into computers using human language. Any type of data be it numbers, letters, special symbols, sound or pictures must first be converted into machine-readable form i. Due to this reason, it is important to understand how a computer together with its peripheral devices handles data in its electronic circuits, on magnetic media and in optical devices.
Data representation in digital circuits Electronic components, such as microprocessor, are made up of millions of electronic circuits. This concept can be compared to switching on and off an electric circuit. This forms a basis for describing data representation in digital computers using the binary number system. Data representation on magnetic media The laser beam reflected from the land is interpreted, as 1.
The laser entering the pot is not reflected. This is interpreted as 0. The reflected pattern of light from the rotating disk falls on a receiving photoelectric detector that transforms the patterns into digital form.
Magnetic technology is mostly used on storage devices that are coated with special magnetic materials such as iron oxide. It has proved difficult to develop devices that can understand natural language directly due to the complexity of natural languages.
All forms of data can be represented in binary system format. Other reasons for the use of binary are that digital devices are more reliable, small and use less energy as compared to analog devices. Bits, bytes, nibble and word The terms bits, bytes, nibble and word are used widely in reference to computer memory and data size. It is the basic unit of data or information in digital computers.
A byte is considered as the basic unit of measuring memory size in computer. The term word length is used as the measure of the number of bits in each word. Patterson , Computer Architecture: Introduction to Computer Engineering. University of London Press. Assembly language Comparison of assemblers Disassembler Instruction set Low-level programming language Machine code Microassembler x86 assembly language.