Distributed system is a collection of independent computers that appears to its users as a single coherent system. It is also a field of computer science that studies distributed systems. A distributed system consists of multiple autonomous computers that communicate through a computer network. The computers interact with each other in order to achieve a common goal.
Grid resources are assigned dynamically at runtime depending on their availability and capability.
Grid computing is refers to combination of computer resource from multiple administrative domain. The Grid can be thought of as a distributed system with non-interactive workloads that involve a large number of files. Grids are a form of distributed computing whereby a "super virtual computer" is composed of many networked loosely coupled computers acting together to perform very large tasks.
How is Grid Computing works?
In a basic grid computing system, every computer can access the resources of every other computer belonging to the network.
Grid computing is a computer network in which each computer's resources are shared with every other computer in the system. Processing power, memory and data storage are all community resources that authorized users can tap into and leverage for specific tasks. A grid computing system can be as simple as a collection of similar computers running on the same operating system or as complex as inter-networked systems comprised of every computer platform you can think of.
The grid computing concept is not a new one. It's a special kind of distributed computing. In distributed computing, different computers within the same network share one or more resources. In the ideal grid computing system, every resource is shared, turning a computer network into a powerful supercomputer. With the right user interface, accessing a grid computing system would look no different than accessing a local machine's resources. Every authorized computer would have access to enormous processing power and storage capacity.
Grid Computing Overview
Grid computing systems work on the principle of pooled resources. Let's say you and a couple of friends decide to go on a camping trip. You own a large tent, so you've volunteered to share it with the others. One of your friends offers to bring food and another says he'll drive the whole group up in his SUV. Once on the trip, the three of you share your knowledge and skills to make the trip fun and comfortable. If you had made the trip on your own, you would need more time to assemble the resources you'd need and you probably would have had to work a lot harder on the trip itself.
A grid computing system uses that same concept: share the load across multiple computers to complete tasks more efficiently and quickly. Before going too much further, let's take a quick look at a computer's resources:
Central processing unit (CPU): A CPU is a microprocessor that performs mathematical operations and directs data to different memory locations. Computers can have more than one CPU.
Memory: In general, a computer's memory is a kind of temporary electronic storage. Memory keeps relevant data close at hand for the microprocessor. Without memory, the microprocessor would have to search and retrieve data from a more permanent storage device such as a hard disk drive.
Storage: In grid computing terms, storage refers to permanent data storage devices like hard disk drives or databases.
Grid computing systems link computer resources together in a way that lets someone use one computer to access and leverage the collected power of all the computers in the system. To the individual user, it's as if the user's computer has transformed into a supercomputer.
Application Grid Computing
Typical Grid Farm
Grid computing concerns the application of the resources of many computers in a network to a single problem at the same time - usually to a scientific or technical problem that requires a great number of computer processing cycles or access to large amounts of data.
Grid computing appears to be a promising trend for three reasons:
(1) its ability to make more cost-effective use of a given amount of computer resources,
(2) as a way to solve problems that can't be approached without an enormous amount of computing power, and
(3) because it suggests that the resources of many computers can be cooperatively and perhaps synergistically harnessed and managed as a collaboration toward a common objective. In some grid computing systems, the computers may collaborate rather than being directed by one managing computer. One likely area for the use of grid computing will be pervasive computing applications - those in which computers pervade our environment without our necessary awareness.
Grid Computation Software
Grid Computing Worldwide
To perform grid computation for joined computers online through the internet, the software which supports grid computation framework must be installed on each computer inside the VO. The software not only handles information queries, storage management, and processing scheduling, but also does authentication and data encryption to ensure information security. Some famous software that supports grid computation is Java CoG Kit, UNICORE (UNiform Interface to COmputing REsources), and IBM Batch-on-Grid. Microsoft is also working on a new version of the Windows system that supports grid computation.
Issue Security in Grid Computing
Authentication
Grid computation shares resources online through the internet, so anyone may access shared resources. Therefore, information security has been very important in the grid computation area. The basic idea of controlling access to shared resources is through authentication. The simplest authentication design is to set up a username and password for the user to join a VO. Over time, the authorization framework and architecture design have been popular research topics in grid computation to ensure better information security.
Cryptography
To prevent unwanted users from stealing information, encryption has been widely used for data transmission. A special cryptography can be designed for each VO to transfer data online. Even if information is stolen by unwanted users, they must have the cryptography scheme or key to decode the data in order to view it.
Hackers, Worms, and Viruses
A VO can have millions of computers running parallel processes to carry out high performance computation. Therefore, it is likely that some of them were infected by computer viruses and worms, or hacked by intruders. The VO may not be damaged if only some of the computers were hacked and part of the information was stolen. However, the computer may be infected with an unwanted program (computer virus) that spreads to infect other computers inside the VO, and finally causes all of the information to be lost. It may be a good idea for all users inside a VO to perform a virus scan before receiving information from other users. Even if the VO has a very safe authentication process, however, the virus can still find a security hole to get in, or spread by e-mail and message passing software like ICQ or MSN.
Some computer worms, which may not be designed for stealing information, can also infect the VO, increase the CPU load, and hinder performance.
