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.

Session Layer

The session layer manages sessions between applications, including initiation, maintenance and termination of information transfer sessions. Usually this is visible to the user by having to log on with a password.

The session layer tracks connections, also called sessions. The session layer should keep track of multiple file downloads requested by a particular FTP application, or multiple telnet connections from a single terminal client, or web page retrievals from a web server.

With TCP/IP this functionality is handled by application software addressing a connection to a remote machine and using a different local port number for each connection.

The session layer performs the following functions:

Communication with the Presentation layer above.

Organize and manage one or more connections per application, between hosts.

Communication with the Transport layer below.

Session layer protocols are particularly useful for multimedia applications for which it is necessary to coordinate the timing of two or more types of data, such as voice and moving images, with a high degree of precision. Examples include video conferencing and streaming.

Examples of session layer protocols include DLC (data link control), PAP (printer access control), SMB (server message block), ASP (AppleTalk session protocol), NetBIOS (network basic input/output system) and ZIP (zone information protocol).

TYPES of Session:

Simplex: Transmission from one side only. eg TV, Radio.

Half Duplex: Transmission from both side but onc side at a time. eg Walkie Takie, Chatting.

Full Duplex: Transmission from both side simultaneously. eg Telephoe, Mobile, Video Chat.

Hub

This is a hardware device that is used to network multiple computers together. It is a central connection for all the computers in a network, which is usually Ethernet-based. Information sent to the hub can flow to any other computer on the network. If you need to connect more than two computers together, a hub will allow you to do so. If you only need to network two computers together, a simple crossover Ethernet cable will do the trick.

An Ethernet hub, active hub, network hub, repeater hub, multiport repeater or hub is a device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the physical layer (layer 1) of the OSI model. The device is a form of multiport repeater. Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision.

Network Hardwares

 

Networking hardware may also be known as network equipment, computer networking devices. Units which are the last receiver or generate data are called hosts or data terminal equipment.

All these terms refer to devices facilitating the use of a computer network. Specifically, they mediate data in a computer network.

 Specific devices

    Hub: a device that connects multiple Ethernet segments, making them act as a single segment. When using a hub, every attached device shares the same broadcast domain and the same collision domain. Therefore, only one computer connected to the hub is able to transmit at a time. Depending on the network topology, the hub provides a basic level 1 OSI model connection among the network objects (workstations, servers, etc.). It provides bandwidth which is shared among all the objects, in contrast to switches, which provide a connection between individual nodes. It works on OSI layer 1.

    Switch: a device that allocates traffic from one network segment to certain lines (intended destination(s)) which connect the segment to another network segment. Unlike a hub, a switch splits the network traffic and sends it to different destinations rather than to all systems on the network. It works on OSI layer 2.

    Repeater: a device which amplifies or regenerates digital signals received while sending them from one part of a network into another. It works on OSI layer 1.

    Router: a specialized network device that determines the next network point to which it can forward a data packet towards the ultimate destination of the packet. Unlike a gateway, it cannot interface different protocols. It works on OSI layer 3.

    Bridge: a device that connects multiple network segments along the data link layer. It works on OSI layer 2.

    Gateway: this device is placed at a network node and interfaces with another network that uses different protocols. It works on OSI layers 4 to 7.

    Network interface controller: a piece of computer hardware allowing the attached computer to communicate by network.

    Wireless network interface controller: a piece of computer hardware allowing the non-attached computer to communicate by LAN.

    Modem: device that modulates an analog "carrier" signal (such as sound) to encode digital information, and that also demodulates such a carrier signal to decode the transmitted information, such as a computer communicating with another computer over a telephone network.