Info-Grade

As we need a highway to travel from one place to another place. Similarly, the input and output of computer system also need a path to transmit data, information and control from one device to another device. The data transmit from input device to CPU, CPU to memory are common examples of system bus. 

The path through which data and instruction flow is called bus of computer. It is a collection of wires, chips and slots inside the computer through which data and information are transmit from one part of computer to another.

Normally, Bus is available from 1 bit and above. The width of the bus determines how much data can moved at a time. Nowadays, PATA cables are replaced by SATA cables because of faster and small in size. These are also a way of transferring data and information from HDD to memory. Beside these cables there are numbers of buses inside the computer system (motherboard). There are three types of System bus they are : 

The pathway through which transmit of address of memory location is called address bus. All types of memory devices have microscopic memory cells which are identified with unique humans known as memory address or memory locations. When the CPU reads data or instruction from memory or writes data to memory, it must specify the address of the memory location it is going to access. Unlike the other buses, the address bus always receive memory location from the CPU. There is one way flow in address bus. 

The pathway (circuit / chips / wires / slots) through which transmit of data from one memory location to other is called Data Bus. When the CPU fetches data from memory, it first output the memory address on its address bus. Then the data bus. When writing data to memory, the CPU first outputs the address onto the address bus, then output the data onto the data bus. Memory the reads and stores the data to the proper location. The data flows in bidirectional way. 

The pathway (circuit / chips / wires / slots) through which transmit of control signal to operate and control devices and software is called control bus. It is different from other two buses. The control bus is the collection of individual control signals for timing and controlling function sent by the control unit to other unit of the system. These signals indicate where data is to read or written, whether the CPU is accessing memory or an input/output device, and whether the I/O device or memory is ready to transfer data.  

Computers which were made approximately between 1941 and 1955 A.D. are classified as the first generation computer. Vacuum Tube is the main technology, which was developed by Lee de forest in 1908 A.D. 

• Technology : Vacuum Tube
• Processing Speed : processing speed was measured in millisecond
• I/O Devices : Punch card was used as input / output devices 
• Compute Type : Computers were electron mechanical 
• Memory : Vacuum tube was used as memory device
• Storage device : First punch card and later magnetic drum
• Operation Mode : Computer should be setup manually as there was no operating system
• Reliability and Accuracy : Not fully reliable and accurate 
• Programming language : Machine level language 
• Size and cost : Very large in size and expensive 
• Availability : available to the military purpose and university research only 
• Power and Heat : Consumed a lot of a electricity and emitted a lot of heat
• Portability : Computer were not portable 
• Example : Mark I, ABC, ENIAC etc. 

Second Generation Computer 

Computer which were made approximately between 1955 to 1964 and having the transistor and diodes as main memory device are classified as the second generation computer. Transistor was designed by Walter Brattain, John Bardeen and William Sockley in 1947 A.D. 

The main features of computer generation are as follows. 

• Technology : Transistor (Main component)
• Processing Speed : Measured in Microsecond
• I/O Devices : punch card was used as input / output device
• Memory: Magnetic core memory is used as internal memory 
• Storage device : Magnetic tape
• Operation mode : Should set up manually as there was not os. 
• Reliability and Accuracy : More reliable and accurate then first generation computer. 
• Programming language : Assembly and high Level language such as FORTRAN, ALGOL, COBOL etc. 
• Size & cost : Smaller and less expensive then first generation 
• Availability : Available for general purpose 
• Power consumption and Heat : Power consumption and heat emission was less then first generation computer. 
• Portable : Not portable 
• IBM 1401, ICL 2950/10, IBM 1620 etc. 

Third Generation Computer 

The computers which were made approximately between 1964 to 1975 and having IC's technology as memory and processing devices are classified as third generation computer. The first IC was developed by Jack Kilby and Robot Noyce in 1985. Later Robert Noyce established Intel company. 

• Technology : IC (Integrated Circuit) 
• Processing Speed : Faster than previous generation computer 
• I/O devices : Keyboard and Monitor
• Computer Type : Electronic 
• Memory : Semiconductor memory (Primary memory)
• Storage Devices : Magnetic disk (Secondary memory)
• Operation Mode : Os was introduced for automatic and multi programming. 
• Reliability and accuracy : Fully reliable and accurate 
• Programming language : High level language for computer programming 
• Size and cost : Smaller in size and less expensive then previous generations of computer 
• Availability : Available for general purpose as well as for personal use. 
• power consumption and heat emission : Power consumption and heat emission was less than previous generation computer
• Potable : Become portable computer because of development of Desktop and Laptop computer 
• Example : IBM 360 Series, ICL 1900 etc, UNIVAC etc. 

Fourth Generation Computer  

The computer which were made approximately between 1975 to till now and having microprocessor as CPU and VLSI and ULSI technology in IC as memory device and classified as fourth generation computer. 

- Microprocessor is a chip in which millions of components are integrated together in different layers. 

- First commercial microprocessor was Intel 4004 made by Intel corporation in 1971 AD. It was 4 bit processor. 

The main features of fourth generation computer are

• Technology : IC's and Microprocessor 
• Processing speed : Faster then previous generations
• I/O devices : Fourth refined and invented various devices such as scanner, touch screen, printer etc. 
• Computer type : Electronic 
• Memory : Semiconductor memory with huge capacity 
• Storage device : Magnetic and optical disk with large storage capacity for secondary storage device. 
• Operation mode : Multi programming, multi processing, multimedia and distributed operating system become possible. 
• Reliability and accuracy : Fully reliable and accurate 
• Programming language : advance HLL and 4GL for application and database programming have been used. 
• Size and cost : Smaller and less expensive then previous generations of computer
• Availability : General purpose as well as special purpose 
• Power consumption and heat emission : It has been less then previous generation of computer
• Portable : Because portable off development of personal or Desktop computer, Laptop, Notebook, PDA etc. 
• Example : Acer ASPIRE 5741, Apple MacBook Air, Dell Inspiration 1400 etc. 

Fifth Generation Computer 

Although the computer of this generation have not come yet in reality, but computers scientist are trying since 1990 A.d. It is said that the computer of this generation will use AI (Artificial Intelligence) and bio-chips as memory devices so that they can think and decide this like a human being. 

Features of fifth generation computer are as follows

• They will be super conductor memory like bio-chips that the speed will be very fast. 
• The computer will be intelligent and knowledge base because of AI. 
• Instead of HLL, natural languages will be used such as English, Nepali, Hindi for giving instruction
• this computer will have power of seance, logic and decision making capacity  

1.      Register transfer micro-operations

2.      Arithmetic micro-operations

3.      Logic micro-operations

4.      Shift micro operations

              R ← ashl R (arithmetic shift left R (register))

RISC is known as Reduced instruction Set Computer. It is a type of microprocessor that has limited number of instructions. It can execute it's instructions very fast because instructions are very small and simple. 

RISC chips require fewer transistors which make them cheaper to design and produce. Most Instructions complete in one cycle, which allows the processor to handle many instructions at same time. In this type of processor, instructions are register based and data transfer takes place from register to register. 

CISC is known as Complex Instruction Set Computer. It was first developed by Intel corporation. It contains large number of complex instructions. In this processor instructions are not register based and instructions cannot be completed in one machine cycle. Data transform is from memory to memory. Micro programmed control unit is found in CISC. It also have variable instruction format. 

Features of CISC

• Complex instruction, hence complex instruction decoding
• Instruction may take more than single clock cycle to get executed
• Instruction are larger than one word size
• Complex addressing mode
• More data types 

Pendrive is one of our must important storage device, where we store our documents or data. Normally, when we pluck our Pendrive to our PC, it displayed default icon every time. We can put our own photo or icon instead of default icon. To change the icon of removable disk / prndrive follow the following steps.  

Before following the steps we should have our own icon/photo and Pendrive.
Step 1: Right click on the picture or icon which you want to set as drive icon and click on Edit.



Step 6: Paste it in Removable Drive (Pendrive)



Step 7: Remove your Removable Drive (Pendrive) and insert again. Your drive icon will be changed.

Video Tutorial 

• Providing programming flexibility to the uses.
• Using the bits in the address field of instruction efficiently

Types of Addressing Modes

1) Implied Addressing Mode

• Address of operands are specified implicit in the definition of instruction.
• It does not need to specify address of instruction
• Example : Add x; Add y; 

• Instead of specifying the address of operand itself is specified in the instruction. 
• No need to specify address in the instruction. 
• However, operand itself need to be specified. 
• Sometimes, require more bits to be address. 
• Fast to acquire an operand

• Address specified in the instruction is the address of register.
• The instruction has the address of the Register where the operand is stored.
• Shorter address then memory address.
• Shorter instructions and faster instruction fetch
• Saving address field to access to the operands 
• It has very limited address space

• In this mode, the instruction specifies the register whose contents give us the address of operand which is in memory. Thus the register contains the address of operand rather than the operand itself. 
• Instruction specifies a register which contains the memory address of operand 
• Saving instruction bits since register address is shorter than memory address
• Slower then register and memory addressing 
• Example:   EA = contend of R

• In this mode the register is increment or decremented after or before its value is used. 
• Instruction specifies the memory address which can be used directly to access the memory. 
• Faster then the memory addressing mode
• Too many bits are needed to specify the address for a physical memory space.
• Example:   EA = IR (Address)

• In this mode, effective address of operand is present in instruction itself. 
• Single memory reference to access data
• No additional calculation to find the effective address of the operand
• For Example: Add R1, 4000, In this the 4000 is effective address of operand.  

        Note : Effective Address is the location where operand is present

7) Indirect Addressing Mode

• The address field of an instruction specifies the address of a memory location that contains the address of the operand. 
• When the abbreviated address is used large physical memory can be addressed with the relatively small number of bits.
• Slow acquire operand because of an additional memory access. 
• Example:    EA = M[IR )address)]

8)  Relative Addressing Mode

The address field of instruction specifies the part of the address which can be used along with a designed register to calculate the address of the operand. 

• Address field of the instruction is short
• Large physical memory can be accessed with a small number of address bits.
• There are three addressing mode

1. PC Relative addressing Mode (EA = IX + IR(address))
2. Indexed Addressing Mode (EA = IX + IR (address)) / [IX is indexed register]
3. Base Register Addressing Mode (EA = A + (R) 

Binary	Octal	Decimal	Hexadecimal
0000	0	0	0
0001	1	1	1
0010	2	2	2
0011	3	3	3
0100	4	4	4
0101	5	5	5
0110	6	6	6
0111	7	7	7
1000	10	8	8
1001	11	9	9
1010	12	10	A
1011	13	11	B
1100	14	12	C
1101	15	13	D
1110	16	14	E
1111	17	15	F

1. Binary Number System : Any number having base or radix 2 and the number consists 0 and 1 only are called binary number system. E.g:  1110^­₂, 1001₂, 111001₂
2. Decimal Number System: Any number having base or radix 8 and the number consists 0, 1, 2, 3, 4, 5, 6 and 7 are called octal number system. E.g: 563^­₈, 1235₈, 5736₈
3. Decimal Number System: Any number having base or radix 10 and the numbers consists 0, 1, 2, ........ 9 are called decimal number system. E.g : 196^­₁₀, 258₁₀, 1236₁₀ 
4. Hexadecimal Number System : Any number having base or radix 16 and the number consists 0, 1, 2, 3, ...... 9 and character consist A, B, C, D, E and F are called hexadecimal number system. Where A=10, B=11, C=13, D=14, E=15 and F=15. E.g : 25A^­₁₆, 156B₁₆, 9D₁₆