Operating System (OS)

An Operating System (OS) is an interface between a computer user and computer hardware. An operating system is a software which performs all the basic tasks like file management, memory management, process management, handling input and output, and controlling peripheral devices such as disk drives and printers.
Some popular Operating Systems include Linux, Windows, OS X, VMS, OS/400, AIX, z/OS, etc

Following are some of important functions of an operating System.

• Memory Management
• Processor Management
• Device Management
• File Management
• Security
• Security
• Networking
• Error detecting aids
• Coordination between other software and users

what is Software ?

Software are the set of programs/packages which we can not touch and feel as like hardware(It is device which we can touch and feel). Software provide better communication between computer/PC and user.
Computer software, or simply software, is that part of a computer system that consists of encoded information or computer instructions, in contrast to the physical hardware from which the system is built.

Software is the combination of instructions to perform the specific task.

Types of Software:- In broad Sense software is categories in two

1)System Software:-System software are those software which we can used to control the system and also used for run applications.

Example:-DOS,Unix, Windows etc.


2)Application Software:-Application software are those software which are designed to perform a specific task. It requires a platform to execute i.e. operating system

Example: Tally, Payroll, VLC Media etc.


 

Types of Information System

The "classic" view of Information systems found  in the 1980s was of a pyramid of systems that reflected the hierarchy of the organization, usually transaction processing systems at the bottom of the pyramid, followed by management information systems, decision support systems, and ending with executive information systems at the top. Although the pyramid model remains useful, since it was first formulated a number of new technologies have been developed and new categories of information systems have emerged, some of which no longer fit easily into the original pyramid model.
Some examples of such systems are:

• data warehouses
• enterprise resource planning
• enterprise systems
• expert systems
• search engines
• geographic information system
• global information system
• office automation.

A computer(-based) information system is essentially an IS using computer technology to carry out some or all of its planned tasks. The basic components of computer-based information systems are:

• Hardware- these are the devices like the monitor, processor, printer and keyboard, all of which work together to accept, process, show data and information.
• Software- are the programs that allow the hardware to process the data.
• Databases- are the gathering of associated files or tables containing related data.
• Networks- are a connecting system that allows diverse computers to distribute resources.
• Procedures- are the commands for combining the components above to process information and produce the preferred output.

The first four components (hardware, software, database, and network) make up what is known as the information technology platform. Information technology workers could then use these components to create information systems that watch over safety measures, risk and the management of data. These actions are known as information technology services.^[19]

Components of Information System

The six components that must come together in order to produce an information system are:

1. Hardware: The term hardware refers to machinery. This category includes the computer itself, which is often referred to as the central processing unit (CPU), and all of its support equipments. Among the support equipments are input and output devices, storage devices and communications devices.
2. Software: The term software refers to computer programs and the manuals (if any) that support them. Computer programs are machine-readable instructions that direct the circuitry within the hardware parts of the system to function in ways that produce useful information from data. Programs are generally stored on some input / output medium, often a disk or tape.
3. Data: Data are facts that are used by programs to produce useful information. Like programs, data are generally stored in machine-readable form on disk or tape until the computer needs them.
4. Procedures: Procedures are the policies that govern the operation of a computer system. "Procedures are to people what software is to hardware" is a common analogy that is used to illustrate the role of procedures in a system.
5. People: Every system needs people if it is to be useful. Often the most over-looked element of the system are the people, probably the component that most influence the success or failure of information systems. This includes "not only the users, but those who operate and service the computers, those who maintain the data, and those who support the network of computers."
6. Feedback: it is another component of the IS, that defines that an IS may be provided with a feedback (Although this component isn't necessary to function).

Data is the bridge between hardware and people. This means that the data we collect is only data, until we involve people. At that point, data is now information.

Information System

" A system which assembles, stores, processes and delivers information relevant to an organisation (or to society) in such a way that the information is accessible and useful to those who wish to use it, including managers, staff, clients and citizens. An information system is a human activity (social) system which may or may not involve the use of computer systems"

An information system (IS) is any organized system for the collection, organization, storage and communication of information. More specifically, it is the study of complementary networks that people and organizations use to collect, filter, process, create and distribute data.
"An information system (IS) is a group of components that interact to produce information"
A computer information system is a system composed of people and computers that processes or interprets information. The term is also sometimes used in more restricted senses to refer to only the software used to run a computerized database or to refer to only a computer system.
Information system is an academic study of systems with a specific reference to information and the complementary networks of hardware and software that people and organizations use to collect, filter, process, create and also distribute data. An emphasis is placed on an Information System having a definitive Boundary, Users, Processors, Stores, Inputs, Outputs and the aforementioned communication networks.
Any specific information system aims to support operations, management and decision-making. An information system is the information and communication technology (ICT) that an organization uses, and also the way in which people interact with this technology in support of business processes.
Some authors make a clear distinction between information systems, computer systems, and business processes. Information systems typically include an ICT component but are not purely concerned with ICT, focusing instead on the end use of information technology. Information systems are also different from business processes. Information systems help to control the performance of business processes.

 

RISC V/s CISC Architechture

What is E-mail?
 
In its simplest form, e-mail is an electronic message sent from one device to another. While many messages go from computer to computer, e-mail can also be sent and received by mobile phones, PDAs and other portable devices. With e-mail, you can send and receive personal and business-related messages with attachments, such as photos and documents. You can also send music, podcasts, video clips and software programs.

How E-mail Works

To send e-mail, you need a connection to the Internet and access to a mail server that forwards your mail to its final destination. The standard protocol used for sending Internet e-mail is called SMTP, short for Simple Mail Transfer Protocol. It works in conjunction with POP--Post Office Protocol--servers. Almost all Internet service providers and all major online services offer at least one e-mail address with every account.
When you send an e-mail message, your computer routes it to an SMTP server. The server looks at the e-mail address (similar to the address on an envelope), then forwards it to the recipient's mail server, where it's stored until the addressee retrieves it. You can send e-mail anywhere in the world to anyone who has an e-mail address. In fact astronauts on the international space station use e-mail to keep in touch with their earth-bound colleagues.
At one time, you could only send text messages without attachments via the Internet. With the advent of MIME, which stands for Multipurpose Internet Mail Extension, and other types of encoding schemes, such as UUencode, you can now send formatted documents, photos, audio and video files. Just make sure that the person to whom you send the attachment has the software capable of opening it.

Difference between CISC and RISC Architecture

CISC | Complex instruction set Computing.

1.very large instruction sets reaching up to and above three hundred seperate instructions.

2. Performance was improved by allowing the simplification of program compilers, as the range of more advanced instructions available led to less refinements having to be made at the compilation process. However, the complexity of the processor hardware and architecture that resulted can cause such chips to be difficult to understand and program for, and also means they can be expensive to produce.

3. more specialized addressing modes and registers also being implemented, with variable length instruction codes.

4. Instruction pipelining can not be implemented easily.

5. Many complex instructions can access memory, such as direct addition between data in two memory locations. 

6. Mainly used in normal PC’s, Workstations and servers .

7. CISC systems shorten execution time by reducing the

number of instructions per program.

8. Examples of CISC Processors: Intel x86.

RISC | Reduced instruction set Computing.

1. Small set of instructions.

2. simplified and reduced instruction set, numbering one hundred instructions or less. because of simple instructions, RISC chips requires fewer transistors to produce processors. Also the reduced instruction set means that the processor can execute the instructions more quickly, potentially allowing for greater speeds. However, only allowing such simple instructions means a greater burden is placed upon the software itself. Less instructions in the instruction set means a greater emphasis on the efficient writing of software with the instructions that are available.

3. Addressing modes are simplified back to four or less, and the length of the codes is fixed in order to allow standardization across the instruction set.

4. Instruction pipelining can be implemented easily.

5. Only LOAD/STORE instructions can access memory.

6. Mainly used for real time applications.

7. RISC systems shorten execution time by reducing the clock

cycles per instruction (i.e. simple instructions take less time
to interpret).

8. Examples of RISC Processors: Atmel AVR, PIC, ARM.


Summary:

               CISC                                                                             RISC 

Large (100 to 300)                  Instruction Set                  Small (100 or less)

Complex (8 to 20)                  Addressing Modes                 Simple (4 or less) 

Specialized and complex         Instruction Format                               Simple

Variable                               Instruction Lengths                                Fixed

Variable                               Execution Cycles                  Standard for most

Higher                                 Cost / CPU Complexity                           Lower

Compilation                         Simplifies                              Processor design

Processor design                  Complicates                                      Software

Difficult                              Instruction Pipeline                                  Easy

8085 architecture

Acumulator:-It is a 8-bit register which is used to perform arithmetical and logical operation. It stores the output of any operation. It also works as registers for i/o accesses.

Temporary Register:-It is a 8-bit register which is used to hold the data on which the acumulator is computing operation. It is also called as operand register because it provides operands to ALU.

Registers:-These are general purposes registers. Microprocessor consists 6 general purpose registers of 8-bit each named as B,C,D,E,H and L.   Generally theses registers are not used for storing the data permanently. It carries the 8-bits data. These are used only during the execution of the instructions.
These registers can also be used to carry the 16 bits data by making the pair of 2 registers. The valid register pairs available are BC,DE HL. We cannot use other pairs except BC,DE and HL. These registers are programmed by user.


ALU:-ALU performs the arithmetic operations and logical operation.

Flag Registers:-It consists of 5 flip flop which changes its status according to the result stored in an accumulator. It is also known as status registers. It is connected to the ALU.
There are five flip-flops in the flag register are as follows:
1.Sign(S)
2.zero(z)
3.Auxiliary carry(AC)
4.Parity(P)
5.Carry(C)
The bit position of the flip flop in flag register is:           

                              

All of the three flip flop set and reset according to the stored result in the accumulator.
1.Sign- If D7 of the result is 1 then sign flag is set otherwise reset. As we know that a number on the D7 always desides the sign of the number.
if D7 is 1: the number is negative.
if D7 is 0: the number is positive.

2.Zeros(Z)-If the result stored in an accumulator is zero then this flip flop is set otherwise it is reset.

3.Auxiliary carry(AC)-If any carry goes from D3 to D4 in the output then it is set otherwise it is reset.

4.Parity(P)-If the no of 1's is even in the output stored in the accumulator then it is set otherwise it is reset for the odd.

5.Carry(C)-If the result stored in an accumulator generates a carry in its final output then it is set otherwise it is reset.

Instruction registers(IR):-It is a 8-bit register. When an instruction is fetched from memory then it is stored in this register.

Instruction Decoder:- Instruction decoder identifies the instructions. It takes the informations from instruction register and decodes the instruction to be performed.

Program Counter:-It is a 16 bit register used as memory pointer. It stores the memory address of the next instruction to be executed. So we can say that this register is used to sequencing the program. Generally the memory have 16 bit addresses so that it has 16 bit memory.
The program counter is set to 0000H.

Stack Pointer:-It is also a 16 bit register used as memory pointer. It points to the memory location called stack. Generally stack is a reserved portion of memory where information can be stores or taken back together.

Timing and Control Unit:-It provides timing and control signal to the microprocessor to perform the various operation.It has three control signal. It controls all external and internal circuits. It operates with reference to clock signal.It synchronizes all the data transfers.
There are three control signal:
1.ALE-Airthmetic Latch Enable, It provides control signal to synchronize the components of microprocessor.
2.RD- This is active low used for reading operation.
3.WR-This is active low used for writing operation.

There are three status signal used in microprocessor S0, S1 and IO/M. It changes its status according the provided input to these pins.
                               

Serial Input Output Control-There are two pins in this unit. This unit is used for serial data communication.

Interrupt Unit-There are 6 interrupt pins in this unit. Generally an external hardware is connected to these pins. These pins provide interrupt signal sent by external hardware to microprocessor and microprocessor sends acknowledgement for receiving the interrupt signal. Generally INTA is used for acknowledgement.


Hardware Interrupt:-
As i have already discussed that there are 6 interrupt pins in the microprocessor used as Hardware Interrupts given below:
TRAP
RST7.5
RST6.5
RST5.5
INTR
INTA is not an interrupt. INTA is used by the Microprocessor for sending
 the acknowledgement. TRAP has highest priority and RST7.5 has second highest priority and so on.

CSMA/CD (Carrier Sense Multiple Access / Collision Detection)

Short for Carrier Sense Multiple Access / Collision Detection, a set of rules determining how network devices respond when two devices attempt to use a data channel simultaneously (called a collision). Standard Ethernet networks use CSMA/CD to physically monitor the traffic on the line at participating stations. If no transmission is taking place at the time, the particular station can transmit. If two stations attempt to transmit simultaneously, this causes a collision, which is detected by all participating stations. After a random time interval, the stations that collided attempt to transmit again. If another collision occurs, the time intervals from which the random waiting time is selected are increased step by step. This is known as exponential back off.

CSMA/CD is a type of contention protocol.  Networks using the CSMA/CD procedure are simple to implement but do not have deterministic transmission characteristics. The CSMA/CD method is internationally standardized in IEEE 802.3.

ETHERNET

Ethernet is a physical and data link layer technology for local area networks (LANs). Ethernet was invented by engineer Robert Metcalfe. A local-area network (LAN) architecture developed by Xerox Corporation in cooperation with DEC and Intel in 1976. Ethernet uses a bus or star topology and supports data transfer rates of 10 Mbps. The Ethernet specification served as the basis for the IEEE 802.3 standard, which specifies the physical and lower software layers. Ethernet uses the CSMA/CD access method to handle simultaneous demands. It is one of the most widely implemented LAN standards.

A newer version of Ethernet, called 100Base-T (or Fast Ethernet), supports data transfer rates of 100 Mbps. And the newest version, Gigabit Ethernet supports data rates of 1 gigabit (1,000 megabits) per second.

Difference between a hub and a switch

Difference between a hub and a switch

A Hub is a networking device that allows one to connect multiple PCs to a single network. Hubs may be based on Ethernet, Firewire, or USB connections. A switch is a control unit that turns the flow of electricity on or of in a circuit. It may also be used to route information patterns in streaming electronic data sent over networks. In the context of a network, a switch is a computer networking device that connects network segments.

Hub	Switch
Physical layer. Hubs are classified as Layer 1 devices per the OSI model.	Data Link Layer. Network switches operate at Layer 2 of the OSI model.
Hubs always perform frame flooding; may be unicast, multicast or broadcast	First broadcast; then unicast & multicast as needed.
4/12 ports	Switch is multi port Bridge. 24/48 ports
A network hub cannot learn or store MAC address.	A network switch stores MAC addresses in a lookup table.
Passive Device (Without Software)	Active Device (With Software) & Networking device
Half duplex	Full duplex
Hub has one Broadcast Domain.	Switch has one broadcast domain [unless VLAN implemented]
LAN	LAN
Electrical signal or bits	Frame (L2 Switch) Frame & Packet (L3 switch)
To connect a network of personal computers together, they can be joined through a central hub.	Allow to connect multiple device and port can be manage, Vlan can create security also can apply
Collisions occur commonly in setups using hubs.	No collisions occur in a full-duplex switch.

OSI

1)It has 7 layers

2)Transport layer gurantees delivery of packets

3)Horizontal approach

4)Seperate presentation layer

5)Seperate session layer

6)Network layer provides both connectionless and connection oriented services

7)It defines the services,interfaces and protocols very clearly and makes a clear distinction between them

8)The protocol are better hidden and can be easily replaced as the technology changes

9)OSI truly is a general model

10)It has a problem of protocol filtering into a model

TCP/IP

1)Has 4 layers

2)Transport layer does not gurantees delivery of packets

3)Vertical approach

4)No session layer, characteristics are provided by transport layer

5)No presentation layer, characteristics are provided by application layer

6)Network layer provides only connection less services

7)It does not clearly distinguishes between service interface and protocols

8)It is not easy to replace the protocols

9)TCP/IP can not be used for any other application

10)The model does not fit any protocol stack.