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UNIT - I
Computer: A computer is a programmable machine. A computer is an electronic device, operating under the control of instructions stored in its own memory The two principal characteristics of a computer are:
- It responds to a specific set of instructions in a well-defined manner and
- it can execute a prerecorded list of instructions (a program). Definition Computer is an electronic data processing device which
- accepts and stores data input,
- processes the data input, and
- Generates the output in a required format. FUNDAMENTALS OF COMPUTER Computer is an advanced electronic device that takes raw data as input from the user and processes it under the control of set of instructions (called program), gives the result (output), and saves it for the future use. Functionalities of a computer Any digital computer carries out five functions in gross terms:
- Takes data as input.
- Stores the data/instructions in its memory and use them when required.
- Processes the data and converts it into useful information.
- Generates the output
- Controls all the above four steps.
Advantages or Characteristics of Computers: Following list demonstrates the advantages of computers in today's arena. Word Length: ▲ A Digital Computer operates on binary digits 0 and 1.
▲ A binary digit is called a bit. ▲ A group of 8 bits is called a byte. ▲ The number of bits that a computer can process at a time in parallel is called its word length. High Speed
- Computer is a very fast device.
- It is capable of performing calculation of very large amount of data.
- The computer has units of speed in microsecond, nanosecond, and even the picoseconds.
- It can perform millions of calculations in a few seconds as compared to man who will spend many months for doing the same task. Accuracy
- In addition to being very fast, computers are very accurate.
- The calculations are 100% error free.
- Computers perform all jobs with 100% accuracy provided that correct input has been given. Storage Capability
- Memory is a very important characteristic of computers.
- A computer has much more storage capacity than human beings.
- It can store large amount of data.
- It can store any type of data such as images, videos, text, audio and many others. Diligence
- Unlike human beings, a computer is free from monotony, tiredness and lack of concentration.
- It can work continuously without any error and boredom.
- It can do repeated work with same speed and accuracy. Versatility
- (^) A computer is a very versatile machine.
- A computer is very flexible in performing the jobs to be done.
- This machine can be used to solve the problems related to various fields.
- At one instance, it may be solving a complex scientific problem and the very next moment it may be playing a card game. Reliability
- A computer is a reliable machine.
- Modern electronic components have long lives.
- Memory : Memory is any physical device capable of storing information temporarily or permanently. For example, Random Access Memory (RAM),
- Input Devices : An input device is any hardware device that sends data to a computer, allowing you to interact with and control the computer.
- Output Devices: An output device is any device used to send data from a computer to another device or user.
- Mass Storage Device: Mass storage devices are those devices on your system available for storing large amounts of data.
Computer - Components
All types of computers following five basic operations for converting raw input data into information useful to their users.
Sr.No. Operation Description 1 Take Input The process of entering data and instructions into the computer system 2 Store Data Saving data and instructions so that they are available for processing as and when required. 3 Processing Data Performing arithmetic, and logical operations on data in order to convert them into useful information. 4 Output Information The process of producing useful information or results for the user, such as a printed report or visual display. 5 Control the workflow
Directs the manner and sequence in which all of the above operations are performed.
Input Unit : This unit contains devices with the help of which we enter data into computer. This unit makes link between user and computer. The input devices translate the information into the form understandable by computer. CPU (Central Processing Unit) CPU is considered as the brain of the computer. CPU performs all types of data processing operations. It stores data, intermediate results and instructions(program). It controls the operation of all parts of computer. CPU itself has following three components
- ALU(Arithmetic Logic Unit)
- Memory Unit
- Control Unit Output Unit Output unit consists of devices with the help of which we get the information from computer. This unit is a link between computer and users. Output devices translate the computer's output into the form understandable by users. Computer - CPU(Central Processing Unit) CPU consists of the following features:
- CPU is considered as the brain of the computer.
- CPU performs all types of data processing operations.
- It stores data, intermediate results and instructions(program).
- It controls the operation of all parts of computer. CPU itself has following three components.
- Memory or Storage Unit
- Control Unit
- ALU(Arithmetic Logic Unit) Memory or Storage Unit This unit can store instructions, data and intermediate results. This unit supplies information to the other units of the computer when needed. It is also known as internal storage unit or main memory or primary storage or Random access memory(RAM). Its size affects speed, power and capability. Primary memory and secondary memory are two types of memories in the computer. Functions of memory unit are:
- It stores all the data and the instructions required for processing.
- It stores intermediate results of processing.
- It stores final results of processing before these results are released to an output device.
1 PC (Personal Computer)
It is a single user computer system having moderately powerful microprocessor 2 WorkStation It is also a single user computer system which is similar to personal computer but have more powerful microprocessor. 3 Mini Computer It is a multi-user computer system which is capable of supporting hundreds of users simultaneously. 4 Main Frame It is a multi-user computer system which is capable of supporting hundreds of users simultaneously. Software technology is different from minicomputer. 5 Supercomputer It is an extremely fast computer which can execute hundreds of millions of instructions per second.
MICRO COMPUTER: Micro computer is a smaller computer of system. Micro computer is called Personal computer It is a Grandchild computer. In which the various integrated circuits and elements of a computer are replaced by single integrated circuit called a “chip”. **Examples are the IBM pc, Apple Macintoshes, Dell. *** The most familiar kind of computer is the micro computer *In the past, micro computers have been considered to be of two types-personal computers and work stations. Features of Micro Computers a) Its storage capacity is low. b) Its rate of acceptance and transfer of data is limited i.e., a maximum of 5 lack bytes / second. c) It is able to accept most high level languages. However it uses an interpreter when running High level language because most micros do not have sufficiently large memory to support Compliers. d) The maximum word length it holds is 16-bits. Advantages a) They are small and portable. b) They are relatively inexpensive. c) They work as soon as they are switched on. d) They have excellent graphic capabilities, e) They do not occupy much space. f) They do not consume much power. Disadvantages a) Micros have a limited storage capacity. b) They are relatively slow. *There are basically three types
- Personal computers (Pc’s)
- Workstations
- Portable computers Personal Computer :
- A computer designed for use by one person at a time.
- These machines ran comparatively easy—to—use applications software such as the word processors, spreadsheets, etc., Workstation: A workstation is a computer intended for individual use that is faster and more capable than a personal computer. Portable Computers: A portable computer is a personal computer that is designed to be easily transported and relocated. 3 Types of Portable computer:
- Laptop or Note book Pc
- Subnotebook
- PDA(Personal Digital Assistants Laptops / notebooks: *Laptops may be either AC powered, battery—powered, or both. *These computers are ideal for users who have to work away from their offices. Subnotebooks: *Subnotebooks are for frequent flyer and life-on-the road professionals. *Subnotebook users give up a full display screen and keyboard in exchange for less weight. PDA: *PDAs are much smaller than the notebooks. *They complain pen input writing recognition, personal organization tools, and communication capabilities in a very small package. MINI COMPUTERS: *They minicomputer is a small general purpose system. *There are more powerful and useful as compared to computer *This computer was a midrange computer. *There his computer is a child computer. Ex: department system and Network server *Minicomputer work well in what are known as Distributed Data Processing (DDP). Physically small computers compared with mainframes. Also called as mid range computer.
b) They process at a rapid speed. c) The main memory ranges from 8 to 64 megabytes. d) They have operations done in parallel, rather than sequentially. They are used in weather Forecasting, supersonic aircrafts design and other works that require billions of calculations Per second. e) They can be used for animated graphics-fluid dynamic calculations etc., Network Computer:. *Network computers are computers with minimal memory, disk storage and processor power designed to connect to a network, especially the internet. *Network computers designed to connect to the internet are sometimes called internet boxes, net pcs and internet appliances. *Network computers are the amount of memory and processor power required by the workstation.
- Network computers designed to connect to the Internet may be called Internet boxes, NetPCs or Internet appliances.
COMPUTER ARCHITECTURE
✓ Computer architecture is the conceptual design and fundamental operational structure of a computer system. ✓ It is a blueprint and functional description of requirements and design implementations for the various parts of a computer, focusing largely on the way by which the central processing unit (CPU) performs internally and accesses addresses in memory. ✓ It may also be defined as the science and art of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals. Computer architecture can be classified into three main categories:
- Instruction Set Architecture, or ISA , is the image of a computing system that is seen by a machine language programmer. It includes the instruction set, word size, memory address modes, processor registers, and address and data formats.
- Computer Organization is a lower level and detailed description of the system that involves how the different parts of the system are interconnected and how they interoperate in order to implement the ISA.
- System Design which includes all of the other hardware components within a computing system such as: - Computer buses and switches - (^) Memory controllers - Direct Memory Access (DMA) - Issues like multi-processing
*The parts of computer as we know it did not appear all at once in one machine created by person. *The components from which computers are built *i.e., computer organization *Set of rules and methods, that describes the functionality organization and implementation of computer system. Concepts of computer architecture :
- Pascal’s machine
- Babbage machine
- First electronic computers
- ENIAC
- Low level language
- High level language
- Typical computer
- CISC & RISC ▲ (^) PASCAL’S MACHINE: *Starting in the 17th^ century, many people began to work on machines that would automate tasks, with result that we still use (in one form or another) today. *It was developed by Blaise Pascal , a 17 th^ century mathematicians and philosopher. *They are first mechanical calculation machine. *It was called Arithmetic calculation
*The first of these computers the mark-1 was put into operation in 1944 and was used until 1959. *It stored and counted numbers is mechanically—using 3000 decimal storage wheels , 1400 rotary dial switches , and 500 miles of wire —but transmitted and read the data electrically. ▲ ENIAC: *In the early 1940’s, a separate computer was developed at the university of Pennsylvania. *These using 18,000 vaccum tubes and 1500 relays to move information through the machine—called the Electronic Numerical Integrated and Calculator or ENIAC. *It was the first all—electronic computer. *General purpose of a numerical solving problems. *They have weighted in 30 tons and the area covered 1,800 sq.ft. *In mid has 1940 to a John Voneumen. *Computer instructions in same language used for data. *Instructions are just numbers is known as Machine Language. Advantages:- *Efficient use of memory *Computers can handle instruction as easily as data` *Easily looking a programs in memory. *Data can overwrite the instruction. ▲ LOW LEVEL LANGUAGE: *Machine language & assembly language are called low level language. *Designed to operate and handle the entire hardware and instruction set architecture of a computer. *In assembly language, each instruction has a one-to-one correspondence to a machine language. *Assembly language helped programmers by allowing the name of each instruction instead of its binary representation. ▲ HIGH LEVEL LANGUAGE: *Where the programmer could state the problem to be solved in a more “natural” and machine— independent form. *These closer to a human language. *Compilers give high—level language programmers several advantages over assembly language programmers. Advantages:
*Programs written on one computer could be run on another by re—compiling the source for the other machine. *Programmers who learn a particular high—level language on one systems typically can use that language on another system. *Optimizing compilers can generate code, which is as efficient as the assembly language programmers. ▲ INSIDE A TYPICAL COMPUTER: *Well’ now shift our focus from the large mainframes computers that drove the earliest developments in computing and take a look at the “computers on a chip” known as microprocessors. *The processor’s job is to accept instruction from the memory and execute those instructions.
- Processors
- Memory
- Peripheral Processors:
- ALU
- (^) Control unit
- Register
- Condition code
- Program code ALU: *ALU is the arithmetic Logic Unit *Perform arithmetic & logic calculation. Control unit: *The control unit is control of data flow. Register: *They have data save temporary. *There is during to the execute time. Condition code: *The condition is true or false checking Ex: if (d<0) Program code: *Contains address of instructions being executed. *This using for total program control.
✓ During the early years, memory was slow and expensive and the programming was done in assembly language. ✓ (^) Since memory was slow and instructions could be retrieved up to 10 times faster from a local ROM than from main memory, ✓ Programmers tried to put as many instructions as possible in a microcode.
*RISC –Reduce Instruction Set Computer
RISC (Reduced Instruction Set Computer) :
✓ (^) RISC is a type of microprocessor that has a relatively limited number of instructions. ✓ It is designed to perform a smaller number of types of computer instructions so that it can operate at a higher speed (perform more million instructions per second, or millions of instructions per second). ✓ Earlier, computers used only 20% of the instructions. Making the other 80% unnecessary. ✓ (^) One advantage of reduced instruction set computers is that they can execute their instructions very fast because the instructions are so simple. ✓ RISC chips require fewer transistors, which makes them cheaper to design and produce. ✓ In a RISC machine, the instruction set contains simple, basic instructions, from which more complex instructions can be composed. ✓ (^) Each instruction is of the same length, so that it may be fetched in a single operation. ✓ Most instructions complete in one machine cycle, which allows the processor to handle several instructions at the same time.
This pipelining is a key technique used to speed up RISC machines.
Advantages:
i) Speed: Since a simplified instruction set allows for a pipelined, superscalar design RISC processors often achieve 2 to 4 times the performance of CISC processor using comparable semiconductor technology and the same clock rates.
ii) Simpler Hardware : Because the instruction set of a RISC processor is so simple, it uses up much less chip space; extra functions, such as memory management units or floating point arithmetic units, can also be placed on the same chip. Smaller chips allow a semiconductor manufacturer to place more parts on a single silicon wafer, which can lower the per-chip cost dramatically.
iii) Shorter Design Cycle : Since RISC processors are simpler than corresponding CISC processors, they can be designed more quickly, and can take advantage of other technological developments sooner than corresponding CISC designs, leading to greater leaps in performance between generations.
CISC RISC Execute low level operation Small set of instructions Many instruction can access Only load / store instructions can access memory Normal PC, workstation, server Read time application Memory of memory Register to register High cycle per second Low cycle per second Multiclock Single clock Ex: intel ×86 Ex : apple, ipad, mac.
COMPUTER – MEMORY UNITS
I. Introduction • Basic units of Measurement II. RAM,ROM,PROM,EPROM • Storage versus Memory III.Auxiliary Storage Devices - Magnetic Tape, Hard Disk, Floppy Disk IV.Optical Disks: CD-R Drive, CD-RW disks, DVD, Blue ray Discs Computer - Memory Units A memory unit is a collection of storage cells together with associated circuits needed to transfer information in and out of storage. The memory stores binary word information in groups of bits called words. Memory unit is:
- The amount of data that can be stored in the storage unit.
- That in which storage capacity is expressed in terms of Bytes. Following are the main memory storage units:
Sr.No. Unit Description
Advantages The advantages of cache memory are as follows:
- Cache memory is faster than main memory.
- It consumes less access time as compared to main memory.
- (^) It stores the program that can be executed within a short period of time.
- It stores data for temporary use. Disadvantages The disadvantages of cache memory are as follows:
- Cache memory has limited capacity.
- It is very expensive. Primary Memory (Main Memory) Primary memory holds only those data and instructions on which computer is currently working. It has limited capacity and data is lost when power is switched off. It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed reside in main memory. It is divided into two subcategories RAM and ROM. Characteristics of Main Memory
- These are semiconductor memories
- It is known as main memory.
- Usually volatile memory.
- Data is lost in case power is switched off.
- It is working memory of the computer.
- Faster than secondary memories.
- (^) A computer cannot run without primary memory. Secondary Memory This type of memory is also known as external memory or non-volatile. It is slower than main memory. These are used for storing data/Information permanently. CPU directly does not access these memories instead they are accessed via input-output routines.
Contents of secondary memories are first transferred to main memory, and then CPU can access it. For example : disk, CD-ROM, DVD etc. Characteristic of Secondary Memory
- These are magnetic and optical memories
- (^) It is known as backup memory.
- It is non-volatile memory.
- Data is permanently stored even if power is switched off.
- It is used for storage of data in a computer.
- Computer may run without secondary memory.
- Slower than primary memories. COMPUTER - RANDOM ACCESS MEMORY RAM(Random Access Memory) is the internal memory of the CPU for storing data, program and program result. It is read/write memory which stores data until the machine is working. As soon as the machine is switched off, data is erased. Access time in RAM is independent of the address that is, each storage location inside the memory is as easy to reach as other locations and takes the same amount of time. Data in the RAM can be accessed randomly but it is very expensive. RAM is volatile, RAM is small, both in terms of its physical size and in the amount of data it can hold. RAM is of two types
- Static RAM (SRAM)
- Dynamic RAM (DRAM) Static RAM (SRAM) The word static indicates that the memory retains its contents as long as power is being supplied. However, data is lost when the power gets down due to volatile nature. SRAM chips use a matrix of 6-transistors and no capacitors. Transistors do not require power to prevent leakage, so SRAM need not have to be refreshed on a regular basis. Because of the extra space in the matrix, SRAM uses more chips than DRAM for the same amount of storage space, thus making the manufacturing costs higher. So SRAM is used as cache memory and has very fast access. Characteristic of the Static RAM
- It has long life
- There is no need to refresh
