Cloud computing is a technology that uses the internet and central remote servers to maintain data and applications. Cloud computing allows consumers and businesses to use applications without installation and access their personal files at any computer with internet access. This technology allows for much more efficient computing by centralizing storage, memory, processing and bandwidth.

A simple example of cloud computing is Yahoo email, Gmail, or Hotmail etc [3]. One doesn't need a software or a server to use them. All a consumer would need is just an internet connection and you can start sending emails. The server and email management software is all on the cloud (internet) and is totally managed by the cloud service provider Yahoo, Google etc. The consumer gets to use the software alone and enjoy the benefits. Figure 1 shows the cloud computing system.

Figure 1. Cloud Computing

In a cloud computing system, there's a significant workload shift. Local computers no longer have to do all the heavy lifting when it comes to running applications. The network of computers that make up the cloud handles them instead. Hardware and software demands on the user's side decrease. The only thing the user's computer needs to be able to run is the cloud computing system's interface software, which can be as simple as a Web browser, and the cloud's network takes care of the rest.

Cloud computing is a general term for anything that involves delivering hosted services over the Internet. These services are broadly divided into three categories: Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS)and Software-as-a-Service (SaaS). The name cloud computing was inspired by the cloud symbol that's often used to represent the Internet in flowcharts and diagrams [2]. Cloud computing providers offer their services according to these fundamental models, where IaaS is the most basic and each higher model abstracts from the details of the lower models [1]. Figure 2 shows the layers of cloud computing.

Figure 2. layers of cloud computing

Cloud computing is the delivery of computing as a service rather than a product, whereby shared resources, software, and information are provided to computers and other devices as a metered service over a network cloud (typically the Internet).

Cloud computing is a marketing term for technologies that provide computation, software, data access, and cloud services that do not require end-user knowledge of the physical location and configuration of the cloud that delivers the services.

Cloud computing providers deliver applications via the internet cloud, which are accessed from web browsers and desktop and mobile apps, while the business software and data clouds are stored on servers at a remote location.

Figure 3 shows an example of Cloud Computing system. And Figure 4 shows working principle of Cloud Computing.

Figure 3. Cloud Computing Example

Figure 4. Cloud Computing Working Principle

As a metaphor for the Internet, "the cloud" is a familiar cliché, but when combined with "computing," the meaning gets bigger and fuzzier. Some analysts and vendors define cloud computing narrowly as an updated version of utility computing: basically virtual servers available over the Internet.

Cloud computing is at an early stage, with a motley crew of providers large and small delivering a slew of cloud based services, from full-blown applications to storage services to spam filtering.

Cloud computing exhibits the following key characteristics:

• Empowerment of end-users of computing resources by putting the provisioning of those resources in their own control, as opposed to the control of a centralized IT service
• Agility improves with users' ability to re-provision technological infrastructure resources.
• Application Programming Interface (API) accessibility to software that enables machines to interact with cloud software in the same way the user interface facilitates interaction between humans and computers. Cloud computing systems typically use REST-based APIs.
• Cost is claimed to be reduced and in a public cloud delivery model capital expenditure is converted to operational expenditure. This is purported to lower barriers to entry, as infrastructure is typically provided by a thirdparty and does not need to be purchased for one-time or infrequent intensive computing tasks. Pricing on a utility computing basis is fine-grained with usage-based options and fewer IT skills are required for implementation (in-house).
• Device and location independence enable users to access systems using a web browser regardless of their location or what device they are using (e.g., PC, mobile phone). As infrastructure is off-site (typically provided by a third-party) and accessed via the Internet, users can connect from anywhere.
• Multi-tenancy enables sharing of resources and costs across a large pool of users thus allowing for: centralization of infrastructure in locations with lower costs (such as real estate, electricity, etc.), peak-load capacity increases (users need not engineer for highest possible load-levels), utilization and efficiency improvements for systems that are often only 10–20% utilized.
• Reliability is improved if multiple redundant sites are used, which makes well-designed cloud computing suitable for business continuity and disaster recovery.
• Scalability and Elasticity via dynamic ("on-demand") provisioning of resources on a fine-grained, self-service basis near real-time, without users having to engineer for peak loads.
• Performance is monitored and consistent and loosely coupled architectures are constructed using web services as the system interface.
• Security could improve due to centralization of data, increased security-focused resources, etc., but concerns can persist about loss of control over certain sensitive data, and the lack of security for stored kernels. Security is often as good as or better than other traditional systems, in part because providers are able to devote resources to solving security issues that many customers cannot afford. However, the complexity of security is greatly increased when data is distributed over a wider area or greater number of devices and in multi-tenant systems that are being shared by unrelated users. In addition, user access to security audit logs may be difficult or impossible. Private cloud installations are in part motivated by users' desire to retain control over the infrastructure and avoid losing control of information security.
• Maintenance of cloud computing applications is easier, because they do not need to be installed on each user's computer.

Once an internet protocol connection is established among several computers, it is possible to share services within any one of the following layers.

Figure 5 shows the layers of Cloud Computing. Figure 6 shows the Cloud Computing Architecture.

Figure 5. Layers of Cloud Computing

Figure 6. Cloud Computing Architecture

• A cloud client consists of computer hardware and/or computer software that relies on cloud computing for application delivery and that is in essence useless without it.
• A cloud application is software provided as a service. It consists of the following: a package of interrelated tasks, the definition of these tasks, and the configuration files, which contain dynamic information about tasks at runtime. Cloud tasks provide compute, storage, communication and management capabilities. What makes a cloud application different from other applications is its elasticity. Cloud applications have the ability to scale out and in.
• Cloud platform services, deliver a computing platform and/or solution stack as a service, often consuming cloud infrastructure and sustaining cloud applications.
• Cloud infrastructure services, also known as "Infrastructure as a Service" (IaaS), deliver computer infrastructure – typically a platform virtualization environment – as a service, along with raw (block) storage and networking.
• The servers layer consists of computer hardware and/or computer software products that are specifically designed for the delivery of cloud services, including multi-core processors, cloud-specific operating systems and combined offerings.

When talking about a cloud computing system, it's helpful to divide it into two sections: the front end and the back end. They connect to each other through a network, usually the Internet. The front end is the side the computer user, or client, sees. The back end is the "cloud" section of the system.

The front end includes the client's computer (or computer network) and the application required to access the cloud computing system. Not all cloud computing systems have the same user interface. Services like Web based e-mail programs leverage existing Web browsers like Internet Explorer or Firefox. Other systems have unique applications that provide network access to clients.

On the back end of the system are the various computers, servers and data storage systems that create the "cloud" of computing services. In theory, a cloud computing system could include practically any computer program you can imagine, from data processing to video games. Usually, each application will have its own dedicated server [1].

A central server administers the system, monitoring traffic and client demands to ensure everything runs smoothly. It follows a set of rules called protocols and uses a special kind of software called middleware.

A cloud computing company has a lot of clients, there's likely to be a high demand for a lot of storage space. Some companies require hundreds of digital storage devices. Cloud computing systems need at least twice the number of storage devices it requires to keep all its clients' information stored. That's because these devices, like all computers, occasionally break down.

The applications of cloud computing are practically limitless. With the right middleware, a cloud computing system could execute all the programs a normal computer could run. Potentially, everything from generic word processing software to customized computer programs designed for a specific company could work on a cloud computing system.

We can use cloud computing for medical data storage and diagnosis.

The terms medical record, health record, and medical chart are used somewhat interchangeably to describe the systematic documentation of a single patient's medical history and care across time within one particular health care provider's jurisdiction. The medical record includes a variety of types of "notes" entered over time by health care professionals, recording observations and administration of drugs and therapies, orders for the administration of drugs and therapies, test results, x-rays, reports, etc [4-8]. The maintenance of complete and accurate medical records is a fundamental requirement of health care providers and is generally enforced as a licensing or certification prerequisite. The terms are used for both the physical folder that exists for each individual patient and for the body of information found therein. A good medical records management system could mean the difference between life and death for some individuals [7].

Medical records have traditionally been compiled and maintained by health care providers, but advances in online data storage have led to the development of Personal Health Records (PHR) that are maintained by patients themselves, often on third-party websites.

We are proposing a countrywide (or preferably worldwide) medical database system using cloud computing.

6.1 The Proposal

• Make a countrywide (or preferably worldwide) database.
• Given every individual has or need own personal, health care data, give every citizen a unique MEDICAL-ID.
• Whenever anyone goes for any medical test, or any other medical supervision, update the data in the database for the particular ID.
• Every diagnostic centre, hospital, doctor's chamber, medical shop, and also every individual should have access to that database.

6.2 Features of the Proposed System

• This way anyone will not need to carry any medical data with them, all the data will be stored in the database and can be accessed from anywhere in the country (or worldwide).
• This way we not only can save data (like x-ray report) from being lost or mutilated, also will get access to data anywhere and whenever we needed.
• When a new test is conducted, the reports will be updated in the database, and when a doctors or panel of doctors' advice is needed doctors only needed to check the database, and update their views about the patient's case. And this way we can also see the others doctors views about a patient case.
• This system can be used for expert's suggestion for a particular patient, just by checking the database by the expert from anywhere of the world without the patient being needed to be present in front of the expert.
• And every individual also should have access that database, so that everyone can check about the current status.

• One of the greatest benefits to using cloud computing technology in medical office environment is ease of access to data as opposed to library rows of physical files.
• One way it's beneficial is access to patient records and office management systems from any platform or device without having to worry about maintaining and managing on-premise hardware and software.
• It can also be especially useful, not only to the medical staff, but office administrators as well.
• Cloud storage solutions can be used to deliver records and applications to tablets and desktop computers in the medical office, allowing patients and office administrators to move away from handwritten forms, duplicate data entry, and error prone record copying.
• Cost savings is another advantage of moving to cloud computing. One can manage infrastructure a lot more effectively and lower the cost needed to support these applications by managing a shared infrastructure mode.

• There are still some barriers for some medical practices. It all starts with change, it's going to change the way people fundamentally understand how things. Also, it's a matter of familiarity, as people become more familiar with it and sees the advantages; they are going to start accepting it more.
• Cost and security concerns are other barriers for many practices. Cloud computing requires some upfront investment, training and education, patient data is extremely sensitive, so there are security and privacy concerns that give pause to new technology adoption. The first thing people worry about is security. Security is always the most prominent concern when dealing with sensitive information such as patient information. They worry about relinquishing control because it's no longer in their office or in their data center.

• Cloud computing is revolutionizing the healthcare industry. Many current desktop applications that medical practices now use require large processing power on the client side, but there is a shift towards cloud computing. It can provide new delivery models to make healthcare more efficient and effective, and at a lower cost to technology budgets.
• Prevalence of new and innovative applications that utilize the cloud will make it easier for doctors to reference patient history, submit referrals, process prescriptions, and interact with the patient community.
• One of the things that need to going to start to see moving forward is more solutions offered in the cloud. The reason for that is in healthcare, we have to balance several things at the same time. We have to balance the fact that infrastructure is getting more complicated moving forward, everywhere from the servers to storage to everything else, and also have a struggle with privacy and security.
• There is going to be a challenge with how will healthcare organizations make all of this data electronic as well as how are they also going to make it private and secure. On top of that, we are seeing organizations and individuals who need access to this information anytime, anywhere, so the ability, whether they access this information on their mobile phone, tablet device, laptop, is becoming increasingly important.