Input/Output OS Software

Basically, input/output software organized in the following four layers:

• Interrupt handlers

• Device drivers

• Device-independent input/output software

• User-space input/output software

In every input/output software, each of the above given four layer has a well-defined function to perform and a well-defined interface to the adjacent layers.

Now let's describe briefly, all the four input/output software layers that are listed above.

Interrupt Handlers

Whenever the interrupt occurs, then the interrupt procedure does whatever it has to in order to handle the interrupt.

Device Drivers

Basically, device drivers is a device-specific code just for controlling the input/output device that are attached to the computer system.

Device-Independent Input/Output Software

In some of the input/output software is device specific, and other parts of that input/output software are device-independent.

The exact boundary between the device-independent software and drivers is device dependent, just because of that some functions that could be done in a device-independent way sometime be done in the drivers, for efficiency or any other reasons.

Here are the list of some functions that are done in the device-independent software:

• Uniform interfacing for device drivers

• Buffering

• Error reporting

• Allocating and releasing dedicated devices

• Providing a device-independent block size

User-Space Input/Output Software

Generally most of the input/output software is within the operating system (OS), and some small part of that input/output software consists of libraries that are linked with the user programs and even whole programs running outside the kernel.

 

Goals of the I/O Software

• A key concept in the design of I/O software is known as device independence. It means that I/O devices should be accessible to programs without specifying the device in advance.

• Uniform Naming, simply be a string or an integer and not depend on the device in any way. In UNIX, all disks can be integrated in the file-system hierarchy in arbitrary ways so the user need not be aware of which name corresponds to which device.

• Error Handling: If the controller discovers a read error, it should try to correct the error itself if it can. If it cannot, then the device driver should handle it, perhaps by just trying to read the block again. In many cases, error recovery can be done transparently at a low level without the upper levels even knowing about the error.

• Synchronous (blocking) and Asynchronous (interrupt-driven) transfers: Most physical I/O is asynchronous, however, some very high-performance applications need to control all the details of the I/O, so some operating systems make asynchronous I/O available to them.

• Buffering: Often data that come off a device cannot be stored directly in their final destination.

• Sharable and Dedicated devices: Some I/O devices, such as disks, can be used by many users at the same time. No problems are caused by multiple users having open files on the same disk at the same time. Other devices, such as printers, have to be dedicated to a single user until that user is finished. Then another user can have the printer. Introducing dedicated (unshared) devices also introduces a variety of problems, such as deadlocks. Again, the operating system must be able to handle both shared and dedicated devices in a way that avoids problems.

 

 

 

Operating System - I/O Hardware

Overview

Computers operate on many kinds of devices. General types include storage devices (disks, tapes),transmission devices (network cards, modems), and human-interface devices (screen, keyboard, mouse). Other devices are more specialized. A device communicates with a computer system by sending signals over a cable or even through the air. The device communicates with the machine via a connection point termed a port (for example, a serial port). If one or more devices use a common set of wires, the connection is called a bus.In other terms, a bus is a set of wires and a rigidly defined protocol that specifies a set of messages that can be sent on the wires.

Daisy chain

When device A has a cable that plugs into device B, and device B has a cable that plugs into device C, and device C plugs into a port on the computer, this arrangement is called a daisy chain. It usually operates as a bus.

Controller

A controller is a collection of electronics that can operate a port, a bus, or a device. A serial-port controller is an example of a simple device controller. This is a single chip in the computer that controls the signals on the wires of a serial port. The SCSI bus controller is often implemented as a separate circuit board (a host adapter) that plugs into the computer. It contains a processor, microcode, and some private memory to enable it to process the SCSI protocol messages. Some devices have their own built-in controllers.

I/O port

An I/O port typically consists of four registers, called the status , control, data-in, and data-outregisters.

Status Register

The status register contains bits that can be read by the host. These bits indicate states such as whether the current command has completed, whether a byte is available to be read from the data-in register, and whether there has been a device error.

Control register

The control register can be written by the host to start a command or to change the mode of a device. For instance, a certain bit in the control register of a serial port chooses between fullduplex and half-duplex communication, another enables parity checking, a third bit sets the word length to 7 or 8 bits, and other bits select one of the speeds supported by the serial port.

Data-in register

The data-in register is read by the host to get input.

Data-out register

The data out register is written by the host to send output.

Polling

Polling is a process by which a host waits for controller response.It is a looping process, reading the status register over and over until the busy bit of status register becomes clear. The controller uses/sets the busy bit when it is busy working on a command, and clears the busy bit when it is ready to accept the next command. The host signals its wish via the command-ready bit in the command register. The host sets the command-ready bit when a command is available for the controller to execute.

In the following example, the host writes output through a port, coordinating with the controller by handshaking

The host repeatedly reads the busy bit until that bit becomes clear.

The host sets the write bit in the command register and writes a byte into the data-out register.

The host sets the command-ready bit.

When the controller notices that the command-ready bit is set, it sets the busy bit.

The controller reads the command register and sees the write command.

It reads the data-out register to get the byte, and does the I/O to the device.

The controller clears the command-ready bit, clears the error bit in the status register to indicate that the device I/O succeeded, and clears the busy bit to indicate that it is finished.

I/O devices

I/O Devices can be categorized into following category.

Human readable

Human Readable devices are suitable for communicating with the computer user. Examples are printers, video display terminals, keyboard etc.

Machine readable

Machine Readable devices are suitable for communicating with electronic equipment. Examples are disk and tape drives, sensors, controllers and actuators.

Communication

Communication devices are suitable for communicating with remote devices. Examples are digital line drivers and modems.

Following are the differences between I/O Devices

Data rate

There may be differences of several orders of magnitude between the data transfer rates.

Application

Different devices have different use in the system

Complexity of Control

A disk is much more complex whereas printer requires simple control interface.

Unit of transfer

Data may be transferred as a stream of bytes or characters or in larger blocks.

Data representation

Different data encoding schemes are used for different devices.

Error Conditions

The nature of errors differs widely from one device to another.

Direct Memory Access (DMA)

Many computers avoid burdening the main CPU with programmed I/O by offloading some of this work to a special purpose processor. This type of processor is called, a Direct Memory Access(DMA) controller. A special control unit is used to transfer block of data directly between an external device and the main memory, without intervention by the processor. This approach is called Direct Memory Access(DMA).

DMA can be used with either polling or interrupt software. DMA is particularly useful on devices like disks, where many bytes of information can be transferred in single I/O operations. When used with an interrupt, the CPU is notified only after the entire block of data has been transferred. For each byte or word transferred, it must provide the memory address and all the bus signals controlling the data transfer. Interaction with a device controller is managed through a device driver.

Handshaking is a process between the DMA controller and the device controller. It is performed via wires using terms DMA request and DMA acknowledge.

 

 

Services of Operating System

An operating system is an interface which provides services to both the user and to the programs. It provides an environment for the program to execute. It also provides users with the services of how to execute programs in a convenient manner. The operating system provides some services to program and also to the users of those programs. The specific services provided by the OS are off course different.

Following are the common services provided by an operating system:

1. Program execution
2. I/O operations
3. File system manipulation
4. Communication
5. Error detection
6. Resource allocation
7. Protection

1) Program Execution

• An operating system must be able to load many kinds of activities into the memory and to run it. The program must be able to end its execution, either normally or abnormally.

• A process includes the complete execution of the written program or code. There are some of the activities which are performed by the operating system:

  • The operating system Loads program into memory

  • It also Executes the program

  • It Handles the program’s execution

  • It Provides a mechanism for process synchronization

  • It Provides a mechanism for process communication

2) I/O Operations

• The communication between the user and devices drivers are managed by the operating system.

• I/O devices are required for any running process. In I/O a file or an I/O devices can be involved.

• I/O operations are the read or write operations which are done with the help of input-output devices.

• Operating system give the access to the I/O devices when it required.

3) File system manipulation

• The collection of related information which represent some content is known as a file. The computer can store files on the secondary storage devices. For long-term storage purpose. examples of storage media include magnetic tape, magnetic disk and optical disk drives like CD, DVD.

• A file system is a collection of directories for easy understand and usage. These directories contain some files. There are some major activities which are performed by an operating system with respect to file management.

  • The operating system gives an access to the program for performing an operation on the file.

  • Programs need to read and write a file.

  • The user can create/delete a file by using an interface provided by the operating system.

  • The operating system provides an interface to the user creates/ delete directories.

  • The backup of the file system can be created by using an interface provided by the operating system.

4) Communication

In the computer system, there is a collection of processors which do not share memory peripherals devices or a clock, the operating system manages communication between all the processes. Multiple processes can communicate with every process through communication lines in the network. There are some major activities that are carried by an operating system with respect to communication.

• Two processes may require data to be transferred between the process.

• Both the processes can be on one computer or a different computer, but are connected through a computer network.

5) Error handling

An error is one part of the system that may cause malfunctioning of the complete system. The operating system constantly monitors the system for detecting errors to avoid some situations. This give relives to the user of the worry of getting an error in the various parts of the system causing malfunctioning.

The error can occur anytime and anywhere. The error may occur anywhere in the computer system like in CPU, in I/O devices or in the memory hardware. There are some activities that are performed by an operating system:

• The OS continuously checks for the possible errors.

• The OS takes an appropriate action to correct errors and consistent computing.

6) Resource management

When there are multiple users or multiple jobs running at the same time resources must be allocated to each of them. There are some major activities that are performed by an operating system:

• The OS manages all kinds of resources using schedulers.

• CPU scheduling algorithm is used for better utilization of CPU.

7) Protection

The owners of information stored in a multi-user computer system want to control its use. When several disjoints processes execute concurrently it should not be possible for any process to interfere with another process. Every process in the computer system must be secured and controlled.

 

What is a Process

?

Process is the execution of a program that performs the actions specified in that program. It can be defined as an execution unit where a program runs. The OS helps you to create, schedule, and terminates the processes which is used by CPU. A process created by the main process is called a child process.

Process operations can be easily controlled with the help of PCB(Process Control Block). You can consider it as the brain of the process, which contains all the crucial information related to processing like process id, priority, state, CPU registers, etc.

What is Process Management?

Process management involves various tasks like creation, scheduling, termination of processes, and a dead lock. Process is a program that is under execution, which is an important part of modern-day operating systems. The OS must allocate resources that enable processes to share and exchange information. It also protects the resources of each process from other methods and allows synchronization among processes.

It is the job of OS to manage all the running processes of the system. It handles operations by performing tasks like process scheduling and such as resource allocation.

Process Architecture

Here, are the Architecture Steps:

• Stack: The Stack stores temporary data like function parameters, returns addresses, and local variables.

• Heap Allocates memory, which may be processed during its run time.

• Data: It contains the variable.

• Text: Text Section includes the current activity, which is represented by the value of the Program Counter.

Process Stages

There are mainly seven stages of a process which are:

• New: The new process is created when a specific program calls from secondary memory/ hard disk to primary memory/ RAM a

• Ready: In a ready state, the process should be loaded into the primary memory, which is ready for execution.

• Waiting: The process is waiting for the allocation of CPU time and other resources for execution.

• Executing: The process is an execution state.

• Blocked: It is a time interval when a process is waiting for an event like I/O operations to complete.

• Suspended: Suspended state defines the time when a process is ready for execution but has not been placed in the ready queue by OS.

• Terminated: Terminated state specifies the time when a process is terminated

Process Control Block(PCB)

Every process is represented in the operating system by a process control block, which is also called a task control block.

Here, are important components of PCB

• Process state: A process can be new, ready, running, waiting, etc.

• Program counter: The program counter lets you know the address of the next instruction, which should be executed for that process.

• CPU registers: This component includes accumulators, index and general-purpose registers, and information of condition code.

• CPU scheduling information: This component includes a process priority, pointers for scheduling queues, and various other scheduling parameters.

• Accounting and business information: It includes the amount of CPU and time utilities like real time used, job or process numbers, etc.

• Memory-management information: This information includes the value of the base and limit registers, the page, or segment tables. This depends on the memory system, which is used by the operating system.

• I/O status information: This block includes a list of open files, the list of I/O devices that are allocated to the process, etc.

Summary:

• A process is defined as the execution of a program that performs the actions specified in that program.

• Process management involves various tasks like creation, scheduling, termination of processes, and a dead lock.

• The important elements of Process architecture are 1)Stack 2) Heap 3) Data, and 4) Text

• The PCB is a full form of Process Control Block. It is a data structure that is maintained by the Operating System for every process

• A process state is a condition of the process at a specific instant of time.

• Every process is represented in the operating system by a process control block, which is also called a task control block.

 

Operating System Types

Single-user systems

A computer system that allows only one user to use the computer at a given time is known as a single-user system. The goals of such systems are maximizing user convenience and responsiveness, instead of maximizing the utilization of the CPU and peripheral devices.

Single-user systems use I/O devices such as keyboards, mice, display screens, scanners, and small printers. They can adopt technology developed for larger operating systems.

They may run different types of operating systems, including DOS, Windows, and MacOS. Linux and UNIX operating systems can also be run in single-user mode.

Batch Systems

Early computers were large machines run from a console with card readers and tape drives as input devices and line printers, tape drives, and card punches as output devices. The user did not interact directly with the system; instead, the user prepared a job, (which consisted of the program, data, and some control information about the nature of the job in the form of control cards) and submitted this to the computer operator. The job was in the form of punch cards, and at some later time, the output was generated by the system. The output consisted of the result of the program, as well as a dump of the final memory and register contents for debugging.

To speed up processing, operators batched together jobs with similar needs and ran them through the computer as a group. For example, all FORTRAN programs were compiled one after the other.

The major task of such an operating system was to transfer control automatically from one job to the next. Such systems in which the user does not get to interact with his jobs and jobs with similar needs are executed in a “batch”, one after the other, are known as batch systems. Digital Equipment Corporation’s VMS is an example of a batch operating system.

Multi-programmed Systems

Such systems organize jobs so that CPU always has one to execute. In this way, CPU utilization is increased. The operating system picks and executes from amongst the available jobs in memory. The job has to wait for some task such as an I/O operation to complete. In a non-multi-programmed system CPU would sit idle while in case of multiprogrammed system, the operating system simply switches to, and executes another job.

Time-sharing systems

These are multi-user and multi-process systems. Multi-user means system allows multiple users simultaneously. In this system, a user can run one or more processes at the same time. Examples of time-sharing systems are UNIX, Linux, Windows server editions.

Real-time systems

Real time systems are used when strict time requirements are placed on the operation of a processor or the flow of data. These are used to control a device in a dedicated application. For example, medical imaging system and scientific experiments.

Operating System Examples

There are many types of operating system. Some most popular examples of operating system are:

Unix Operating System

Unix was initially written in assembly language. Later on, it was replaced by C, and Unix, rewritten in C and was developed into a large, complex family of inter-related operating systems. The major categories include BSD, and Linux.

“UNIX” is a trademark of The Open Group which licenses it for use with any operating system that has been shown to conform to their definitions.

macOS

Mac-OS is developed by Apple Inc. and is available on all Macintosh computers. It was formerly called “Mac OS X” and later on “OS X”.  MacOS was developed in 1980s by NeXT and that company was purchased by Apple in 1997.

Linux

Linux is Unix-like operating system and was developed without any Unix code. Linux is open license model and code is available for study and modification. It has superseded Unix on many platforms. Linux is commonly used smartphones and smartwatches.

Microsoft Windows

Microsoft Windows is most popular and widely used operating system. It was designed and developed by Microsoft Corporation. The current version of operating system is Windows-10.

Microsoft Windows was first released in 1985. In 1995, Windows 95 was released which only used MS-DOS as a bootstrap.

 

Operating System Components

An operating system has various components that perform different tasks for proper execution of programs. Following are main components of the operating system.

Process Management

A process can be a program in execution that needs resources like CPU time, memory, files and I/O devices to accomplish its tasks. The operating system is responsible for

• Creating and terminating user and system processes
• Suspending and resuming processes
• Providing mechanisms for process synchronization
• Providing mechanisms for process communication
• Providing mechanisms for deadlock handling

Main Memory Management

Main memory is a large array of words or bytes. These bytes are called memory locations and range in size from hundreds of thousands to billions. Every word or byte has its own address. Main memory is a repository of quickly accessible data shared by the CPU and I/O devices. It contains the code, data, stack, and other parts of a process. The central processor reads instructions of a process from main memory during the machine cycle. The OS is responsible for the following activities in connection with memory management.

• Keeping track of free memory space
• Keeping track of which parts of memory are currently being used and by whom
• Deciding which processes are to be loaded into memory when memory space becomes available
• Deciding how much memory is to be allocated to a process
• Allocating and deallocating memory space as needed
• Ensuring that a process is not overwritten on top of another

Secondary Storage Management

The programs to be executed, along with the data they access, must be in the main memory or primary storage during their execution. Since main memory is too small to accommodate all data and programs, and because the data it holds are lost when the power is lost, the computer system must provide secondary storage to backup main memory. Most programs are stored on a disk until loaded into the memory and then use disk as both the source and destination of their processing. Like all other resources in a computer system, proper management of disk storage is important.
The operating system is responsible for the following activities in connection with disk management:

• Free-space management
• Storage allocation and deallocation
• Disk scheduling

Input/Output Management

The input and output subsystem consists of:

• A memory management component that includes buffering, caching and spooling
• A general device-driver interface
• Drivers for specific hardware devices

File Management

Computers can store information on several types of physical media, e.g. magnetic tape, magnetic disk and an optical disk. The operating system maps files onto physical media and accesses these media through storage devices. Operating system is responsible for the following activities pertaining to file management:

• Creating and deleting files
• Creating and deleting directories
• Supporting primitives (operations) for manipulating files and directories
• Mapping files onto the secondary storage
• Backing up files on stable (nonvolatile) storage media

Protection System

If a computer system has multiple users and allows concurrent execution of multiple processes then the various processes must be protected from each other’s activities. Protection is any mechanism for controlling the access of programs, processes or users to the resources defined by a computer system.

Networking

A distributed system is a collection of processors that do not share memory, peripheral devices or a clock. Instead, each processor has it own local memory and clock, and the processors communicate with each other through various communication lines, such as high- speed buses or networks.

The processors in a communication system are connected through a communication network. The communication network design must consider message routing and connection strategies and the problems of contention and security.

A distributed system collects physically separate, possibly heterogeneous, systems into a single coherent system, providing the user with access to the various resources that the system maintains.

Command Line Interpreter

One of the most important system programs for an operating system is the command interpreter, which is the interface between the user and operating system. Its purpose is to read user commands and try to execute them. Some operating systems include the command interpreter in the kernel. Other operating systems (for example UNIX, Linux, and DOS) treat it as a special program that runs when a job is initiated or when a user first logs on (on time-sharing systems). Examples of shells for UNIX and Linux are Bourne shell (sh), C shell (csh), Bourne Again shell (bash), TC shell (tcsh), and Korn shell (ksh). You can use any of these shells by running the corresponding command, listed in parentheses for each shell.

 

 

Operating System (OS) Overview

Operating System is an interface between the user and the hardware and enables the interaction of a computer’s hardware and software.

Also, an operating system is a software which performs all the basic tasks like file management, memory management, storage management, process management, handling input and output, and controlling peripheral devices such as disk drives and printers.

Types of Operating System (OS) 

All different operating system types are listed below –

• Windows
• iOS
• MAC OS
• Ubuntu
• Novell Netware
• Unix
• Linux

Mobile Operating System

These are some of Mobile Operating System –

• iOS
• Symbian
• Blackberry
• Windows
• Android OS
• Bada

Operating System Functions 

All  Operating system functions are shared below –

1. DEVICE MANAGEMENT –

Operating System manages device communication via their respective drivers.

It does the following activities for device management −

• Keeps tracks of all devices. I/O controller is responsible for this task
• Decides which process gets the device when and for how much time.
• Allocates the device in an efficient way.
• De-allocates devices.

2. FILE MANAGEMENT –

The operating system allocates and de-allocates resources. It regulates which process gets the file and for what duration. Also, it keeps track of information, location, uses, status etc.

The collective facilities are often known as a file system. OS also performs tasks like creating directories and files, copying/moving them and renaming/deleting files.

3. MEMORY MANAGEMENT –

Memory management refers to the management of primary or main memory. Main memory provides fast storage which can be accessed directly by CPU.

When the program is executed and finished, the memory area is freed which can be used for other programs. Computer memory is arranged such that fastest registers come 1st followed by the CPU cache, random access memory, and then disk storage.

The operating system’s memory manager coordinates the use of various types of memory, which is to be allocated or de-allocated and how to move data between them 

4. PROCESS MANAGEMENT –

Every program running on a computer is a process whether it is in the background or in frontend. The operating system is responsible for making multiple tasks to run at the same time (multitasking).

Operating system finds the status of processor and processes, chooses job and its processor allocates processor to process and de-allocates process when it’s executed.

5. MASTERMIND –

Mastermind is one term we can rightfully use for Operating system. Reason – Operating system performs a multitude of functions which only can be performed by super-intelligent mind hence the term “Mastermind”.

• OS provides Booting without an Operating System
• Provides Facility to increase the Logical Memory of the Computer System by using the Physical Memory of the Computer System.
• OS controls the Errors that have been Occurred into the Program
• Provides Recovery of the System when the System gets Damaged.
• Operating System breaks the large program into the Smaller Programs those are also called as the threads. And execute those threads one by one

6. STORAGE MANAGEMENT –

Operating System controls all Storage Operations. Some of these include – how to store data or files into the computers and how users will access the files. The operating system is Responsible for Storing and Accessing the Files. Creation of Files, Creation of Directories and Reading and Writing the data of Files and Directories and also Copy the contents of the Files and the Directories from One Place to Another Place.

 

Software Development Life Cycle

The Software Development Life Cycle (SDLC) refers to a methodology with clearly defined processes for creating high-quality software. in detail, the SDLC methodology focuses on the following phases of software development:

• Requirement analysis

• Planning

• Software design such as architectural design

• Software development

• Testing

• Deployment

This article will explain how SDLC works, dive deeper in each of the phases, and provide you with examples to get a better understanding of each phase.

What is the software development life cycle?

SDLC or the Software Development Life Cycle is a process that produces software with the highest quality and lowest cost in the shortest time possible. SDLC provides a well-structured flow of phases that help an organization to quickly produce high-quality software which is well-tested and ready for production use.

The SDLC involves six phases as explained in the introduction. Popular SDLC models include the waterfall model,spiral model, and Agile model.

How the SDLC Works

SDLC works by lowering the cost of software development while simultaneously improving quality and shortening production time. SDLC achieves these apparently divergent goals by following a plan that removes the typical pitfalls of software development projects. That plan starts by evaluating existing systems for deficiencies.

Next, it defines the requirements of the new system. It then creates the software through the stages of analysis, planning, design, development, testing, and deployment. By anticipating costly mistakes like failing to ask the end-user or client for feedback, SLDC can eliminate redundant rework and after-the-fact fixes.

It’s also important to know that there is a strong focus on the testing phase. As the SDLC is a repetitive methodology, you have to ensure code quality at every cycle. Many organizations tend to spend few efforts on testing while a stronger focus on testing can save them a lot of rework, time, and money. Be smart and write the right types of tests.

Stages and Best Practices

Following the best practices and/or stages of SDLC ensures the process works in a smooth, efficient, and productive way.

1. Identify the Current Problems 

“What are the current problems?” This stage of the SDLC means getting input from all stakeholders, including customers, salespeople, industry experts, and programmers. Learn the strengths and weaknesses of the current system with improvement as the goal.

2. Plan

“What do we want?” In this stage of the SDLC, the team determines the cost and resources required for implementing the analyzed requirements. It also details the risks involved and provides sub-plans for softening those risks.

In other words, the team should determine the feasibility of the project and how they can implement the project successfully with the lowest risk in mind.

3. Design

“How will we get what we want?” This phase of the SDLC starts by turning the software specifications into a design plan called the Design Specification. All stakeholders then review this plan and offer feedback and suggestions. It’s crucial to have a plan for collecting and incorporating stakeholder input into this document. Failure at this stage will almost certainly result in cost overruns at best and the total collapse of the project at worst.

4. Build

“Let’s create what we want.”

At this stage, the actual development starts. It’s important that every developer sticks to the agreed blueprint. Also, make sure you have proper guidelines in place about the code style and practices.

For example, define a nomenclature for files or define a variable naming style such as camelCase. This will help your team to produce organized and consistent code that is easier to understand but also to test during the next phase.

5. Code Test

“Did we get what we want?” In this stage, we test for defects and deficiencies. We fix those issues until the product meets the original specifications.

In short, we want to verify if the code meets the defined requirements.

6. Software Deployment

“Let’s start using what we got.”

At this stage, the goal is to deploy the software to the production environment so users can start using the product. However, many organizations choose to move the product through different deployment environments such as a testing or staging environment.

This allows any stakeholders to safely play with the product before releasing it to the market. Besides, this allows any final mistakes to be caught before releasing the product.

The most common SDLC examples or SDLC models are listed below.

Waterfall Model

This SDLC model is the oldest and most straightforward. With this methodology, we finish one phase and then start the next. Each phase has its own mini-plan and each phase “waterfalls” into the next. The biggest drawback of this model is that small details left incomplete can hold up the entire process.

Agile Model

The Agile SDLC model separates the product into cycles and delivers a working product very quickly. This methodology produces a succession of releases. Testing of each release feeds back info that’s incorporated into the next version. According to Robert Half, the drawback of this model is that the heavy emphasis on customer interaction can lead the project in the wrong direction in some cases.

Iterative Model

This SDLC model emphasizes repetition. Developers create a version very quickly and for relatively little cost, then test and improve it through rapid and successive versions. One big disadvantage here is that it can eat up resources fast if left unchecked.

V-Shaped Model

An extension of the waterfall model, this SDLC methodology tests at each stage of development. As with waterfall, this process can run into roadblocks.

Big Bang Model

This high-risk SDLC model throws most of its resources at development and works best for small projects. It lacks the thorough requirements definition stage of the other methods.

Spiral Model

The most flexible of the SDLC models, the spiral model is similar to the iterative model in its emphasis on repetition. The spiral model goes through the planning, design, build and test phases over and over, with gradual improvements at each pass.

Benefits of the SDLC

SDLC done right can allow the highest level of management control and documentation. Developers understand what they should build and why. All parties agree on the goal upfront and see a clear plan for arriving at that goal. Everyone understands the costs and resources required.

Several pitfalls can turn an SDLC implementation into more of a roadblock to development than a tool that helps us. Failure to take into account the needs of customers and all users and stakeholders can result in a poor understanding of the system requirements at the outset. The benefits of SDLC only exist if the plan is followed faithfully.