Computer – Generations
Generation in computer terminology is a change in technology a computer is/was being used. Initially, the generation term was used to distinguish between varying hardware technologies. Nowadays, generation includes both hardware and software, which together make up an entire computer system.
There are five computer generations known till date. Each generation has been discussed in detail along with their time period and characteristics. In the following table, approximate dates against each generation has been mentioned, which are normally accepted.
Following are the main five generations of computers.
|S.No||Generation & Description|
The period of first generation: 1946-1959. Vacuum tube based.
The period of second generation: 1959-1965. Transistor based.
The period of third generation: 1965-1971. Integrated Circuit based.
The period of fourth generation: 1971-1980. VLSI microprocessor based.
The period of fifth generation: 1980-onwards. ULSI microprocessor based.
Computer – Types
Computers can be broadly classified by their speed and computing power.
|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, similar to personal computer however has a more powerful microprocessor.|
|3||Mini Computer||It is a multi-user computer system, capable of supporting hundreds of users simultaneously.|
|4||Main Frame||It is a multi-user computer system, 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.|
PC (Personal Computer)
A PC can be defined as a small, relatively inexpensive computer designed for an individual user. PCs are based on the microprocessor technology that enables manufacturers to put an entire CPU on one chip. Businesses use personal computers for word processing, accounting, desktop publishing, and for running spreadsheet and database management applications. At home, the most popular use for personal computers is playing games and surfing the Internet.
Although personal computers are designed as single-user systems, these systems are normally linked together to form a network. In terms of power, now-a-days high-end models of the Macintosh and PC offer the same computing power and graphics capability as low-end workstations by Sun Microsystems, Hewlett-Packard, and Dell.
Workstation is a computer used for engineering applications (CAD/CAM), desktop publishing, software development, and other such types of applications which require a moderate amount of computing power and relatively high quality graphics capabilities.
Workstations generally come with a large, high-resolution graphics screen, large amount of RAM, inbuilt network support, and a graphical user interface. Most workstations also have mass storage device such as a disk drive, but a special type of workstation, called diskless workstation, comes without a disk drive.
Common operating systems for workstations are UNIX and Windows NT. Like PC, workstations are also single-user computers like PC but are typically linked together to form a local-area network, although they can also be used as stand-alone systems.
It is a midsize multi-processing system capable of supporting up to 250 users simultaneously.
Mainframe is very large in size and is an expensive computer capable of supporting hundreds or even thousands of users simultaneously. Mainframe executes many programs concurrently and supports many simultaneous execution of programs.
Supercomputers are one of the fastest computers currently available. Supercomputers are very expensive and are employed for specialized applications that require immense amount of mathematical calculations (number crunching).
For example, weather forecasting, scientific simulations, (animated) graphics, fluid dynamic calculations, nuclear energy research, electronic design, and analysis of geological data (e.g. in petrochemical prospecting).
Computer – CPU(Central Processing Unit)
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 the 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 other units of the computer when needed. It is also known as internal storage unit or the main memory or the 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 the memory unit are −
- It stores all the data and the instructions required for processing.
- It stores intermediate results of processing.
- It stores the final results of processing before these results are released to an output device.
- All inputs and outputs are transmitted through the main memory.
This unit controls the operations of all parts of the computer but does not carry out any actual data processing operations.
Functions of this unit are −
- It is responsible for controlling the transfer of data and instructions among other units of a computer.
- It manages and coordinates all the units of the computer.
- It obtains the instructions from the memory, interprets them, and directs the operation of the computer.
- It communicates with Input/Output devices for transfer of data or results from storage.
- It does not process or store data.
ALU (Arithmetic Logic Unit)
This unit consists of two subsections namely,
- Arithmetic Section
- Logic Section
Function of arithmetic section is to perform arithmetic operations like addition, subtraction, multiplication, and division. All complex operations are done by making repetitive use of the above operations.
Function of logic section is to perform logic operations such as comparing, selecting, matching, and merging of data.
Computer – Memory
A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in the computer, where data is to be processed and instructions required for processing are stored. The memory is divided into large number of small parts called cells. Each location or cell has a unique address, which varies from zero to memory size minus one. For example, if the computer has 64k words, then this memory unit has 64 * 1024 = 65536 memory locations. The address of these locations varies from 0 to 65535.
Memory is primarily of three types −
- Cache Memory
- Primary Memory/Main Memory
- Secondary Memory
Cache memory is a very high speed semiconductor memory which can speed up the CPU. It acts as a buffer between the CPU and the main memory. It is used to hold those parts of data and program which are most frequently used by the CPU. The parts of data and programs are transferred from the disk to cache memory by the operating system, from where the CPU can access them.
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.
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 the computer is currently working. It has a 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 resides in the main memory. It is divided into two subcategories RAM and ROM.
Characteristics of Main Memory
- These are semiconductor memories.
- It is known as the main memory.
- Usually volatile memory.
- Data is lost in case power is switched off.
- It is the working memory of the computer.
- Faster than secondary memories.
- A computer cannot run without the primary memory.
This type of memory is also known as external memory or non-volatile. It is slower than the 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. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. For example, disk, CD-ROM, DVD, etc.
Characteristics of Secondary Memory
- These are magnetic and optical memories.
- It is known as the backup memory.
- It is a 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 the secondary memory.
- Slower than primary memories.
Introduction to Operating Systems
A computer system has many resources (hardware and software), which may be require to complete a task. The commonly required resources are input/output devices, memory, file storage space, CPU etc. The operating system acts as a manager of the above resources and allocates them to specific programs and users, whenever necessary to perform a particular task. Therefore operating system is the resource manager i.e. it can manage the resource of a computer system internally. The resources are processor, memory, files, and I/O devices. In simple terms, an operating system is the interface between the user and the machine.
Components of Computer
Two Views of Operating System
Operating System: User View
The user view of the computer refers to the interface being used. Such systems are designed for one user to monopolize its resources, to maximize the work that the user is performing. In these cases, the operating system is designed mostly for ease of use, with some attention paid to performance, and none paid to resource utilization.
Operating System: System View
Operating system can be viewed as a resource allocator also. A computer system consists of many resources like – hardware and software – that must be managed efficiently. The operating system acts as the manager of the resources, decides between conflicting requests, controls execution of programs etc.
Operating System Management Tasks
Processor management which involves putting the tasks into order and pairing them into manageable size before they go to the CPU.
Memory management which coordinates data to and from RAM (random-access memory) and determines the necessity for virtual memory.
Device management which provides interface between connected devices.
Storage management which directs permanent data storage.
Application which allows standard communication between software and your computer.
User interface which allows you to communicate with your computer.
Functions of Operating System
It boots the computer
It performs basic computer tasks e.g. managing the various peripheral devices e.g. mouse, keyboard
It provides a user interface, e.g. command line, graphical user interface (GUI)
It handles system resources such as computer’s memory and sharing of the central processing unit(CPU) time by various applications or peripheral devices.
It provides file management which refers to the way that the operating system manipulates, stores, retrieves and saves data.
Error Handling is done by the operating system. It takes preventive measures whenever required to avoid errors.
Types of Operating Systems
Following are some of the most widely used types of Operating system.
Simple Batch System
Multiprogramming Batch System
Distributed Operating System
Realtime Operating System
Simple Batch Systems
In this type of system, there is no direct interaction between user and the computer.
The user has to submit a job (written on cards or tape) to a computer operator.
Then computer operator places a batch of several jobs on an input device.
Jobs are batched together by type of languages and requirement.
Then a special program, the monitor, manages the execution of each program in the batch.
The monitor is always in the main memory and available for execution.
Advantages of Simple Batch Systems
No interaction between user and computer.
No mechanism to prioritise the processes.
Simple Batch Systems
Multiprogramming Batch Systems
In this the operating system picks up and begins to execute one of the jobs from memory.
Once this job needs an I/O operation operating system switches to another job (CPU and OS always busy).
Jobs in the memory are always less than the number of jobs on disk(Job Pool).
If several jobs are ready to run at the same time, then the system chooses which one to run through the process of CPU Scheduling.
In Non-multiprogrammed system, there are moments when CPU sits idle and does not do any work.
In Multiprogramming system, CPU will never be idle and keeps on processing.
Time Sharing Systems are very similar to Multiprogramming batch systems. In fact time sharing systems are an extension of multiprogramming systems.
In Time sharing systems the prime focus is on minimizing the response time, while in multiprogramming the prime focus is to maximize the CPU usage.
Multiprogramming Batch Systems
A Multiprocessor system consists of several processors that share a common physical memory. Multiprocessor system provides higher computing power and speed. In multiprocessor system all processors operate under single operating system. Multiplicity of the processors and how they do act together are transparent to the others.
Advantages of Multiprocessor Systems
Execution of several tasks by different processors concurrently, increases the system’s throughput without speeding up the execution of a single task.
If possible, system divides task into many subtasks and then these subtasks can be executed in parallel in different processors. Thereby speeding up the execution of single tasks.
Earlier, CPUs and PCs lacked the features needed to protect an operating system from user programs. PC operating systems therefore were neither multiuser nor multitasking. However, the goals of these operating systems have changed with time; instead of maximizing CPU and peripheral utilization, the systems opt for maximizing user convenience and responsiveness. These systems are called Desktop Systems and include PCs running Microsoft Windows and the Apple Macintosh. Operating systems for these computers have benefited in several ways from the development of operating systems for mainframes.
Microcomputers were immediately able to adopt some of the technology developed for larger operating systems. On the other hand, the hardware costs for microcomputers are sufficiently low that individuals have sole use of the computer, and CPU utilization is no longer a prime concern. Thus, some of the design decisions made in operating systems for mainframes may not be appropriate for smaller systems.
Distributed Operating System
The motivation behind developing distributed operating systems is the availability of powerful and inexpensive microprocessors and advances in communication technology.
These advancements in technology have made it possible to design and develop distributed systems comprising of many computers that are inter connected by communication networks. The main benefit of distributed systems is its low price/performance ratio.
Advantages Distributed Operating System
As there are multiple systems involved, user at one site can utilize the resources of systems at other sites for resource-intensive tasks.
Less load on the Host Machine.
Types of Distributed Operating Systems
Following are the two types of distributed operating systems used:
Centralized systems today act as server systems to satisfy requests generated by client systems. The general structure of a client-server system is depicted in the figure below:
Server Systems can be broadly categorized as: Compute Servers and File Servers.
Compute Server systems, provide an interface to which clients can send requests to perform an action, in response to which they execute the action and send back results to the client.
File Server systems, provide a file-system interface where clients can create, update, read, and delete files.
The growth of computer networks – especially the Internet and World Wide Web (WWW) – has had a profound influence on the recent development of operating systems. When PCs were introduced in the 1970s, they were designed for personal use and were generally considered standalone computers. With the beginning of widespread public use of the Internet in the 1990s for electronic mail and FTP, many PCs became connected to computer networks.
In contrast to the Tightly Coupled systems, the computer networks used in these applications consist of a collection of processors that do not share memory or a clock. Instead, each processor has its own local memory. The processors communicate with one another through various communication lines, such as high-speed buses or telephone lines. These systems are usually referred to as loosely coupled systems ( or distributed systems). The general structure of a client-server system is depicted in the figure below:
Like parallel systems, clustered systems gather together multiple CPUs to accomplish computational work.
Clustered systems differ from parallel systems, however, in that they are composed of two or more individual systems coupled together.
The definition of the term clustered is not concrete; the general accepted definition is that clustered computers share storage and are closely linked via LAN networking.
Clustering is usually performed to provide high availability.
A layer of cluster software runs on the cluster nodes. Each node can monitor one or more of the others. If the monitored machine fails, the monitoring machine can take ownership of its storage, and restart the application(s) that were running on the failed machine. The failed machine can remain down, but the users and clients of the application would only see a brief interruption of service.
Asymmetric Clustering – In this, one machine is in hot standby mode while the other is running the applications. The hot standby host (machine) does nothing but monitor the active server. If that server fails, the hot standby host becomes the active server.
Symmetric Clustering – In this, two or more hosts are running applications, and they are monitoring each other. This mode is obviously more efficient, as it uses all of the available hardware.
Parallel Clustering – Parallel clusters allow multiple hosts to access the same data on the shared storage. Because most operating systems lack support for this simultaneous data access by multiple hosts, parallel clusters are usually accomplished by special versions of software and special releases of applications.
Clustered technology is rapidly changing. Clustered system’s usage and it’s features should expand greatly as Storage Area Networks(SANs). SANs allow easy attachment of multiple hosts to multiple storage units. Current clusters are usually limited to two or four hosts due to the complexity of connecting the hosts to shared storage.
Real Time Operating System
It is defined as an operating system known to give maximum time for each of the critical operations that it performs, like OS calls and interrupt handling.
The Real-Time Operating system which guarantees the maximum time for critical operations and complete them on time are referred to as Hard Real-Time Operating Systems.
While the real-time operating systems that can only guarantee a maximum of the time, i.e. the critical task will get priority over other tasks, but no assurity of completeing it in a defined time. These systems are referred to as Soft Real-Time Operating Systems.
Handheld systems include Personal Digital Assistants(PDAs), such as Palm-Pilots or Cellular Telephones with connectivity to a network such as the Internet. They are usually of limited size due to which most handheld devices have a small amount of memory, include slow processors, and feature small display screens.
Many handheld devices have between 512 KB and 8 MB of memory. As a result, the operating system and applications must manage memory efficiently. This includes returning all allocated memory back to the memory manager once the memory is no longer being used.
Currently, many handheld devices do not use virtual memory techniques, thus forcing program developers to work within the confines of limited physical memory.
Processors for most handheld devices often run at a fraction of the speed of a processor in a PC. Faster processors require more power. To include a faster processor in a handheld device would require a larger battery that would have to be replaced more frequently.
The last issue confronting program designers for handheld devices is the small display screens typically available. One approach for displaying the content in web pages is web clipping, where only a small subset of a web page is delivered and displayed on the handheld device.