For many research and engineering projects, the quality of the research or the product is heavily dependent upon the quantity of computing cycles available. It is not uncommon to find problems that require weeks or months of computation to solve. Scientists and engineers engaged in this sort of work need a computing environment that delivers large amounts of computational power over a long period of time. Such an environment is called a High-Throughput Computing (HTC) environment. In contrast, High Performance Computing (HPC) environments deliver a tremendous amount of compute power over a short period of time. HPC environments are often measured in terms of FLoating point Operations Per Second (FLOPS). A growing community is not concerned about operations per second, but operations per month or per year. Their problems are of a much larger scale. They are more interested in how many jobs they can complete over a long period of time instead of how fast an individual job can complete.
The key to HTC is to efficiently harness the use of all available resources. Years ago, the engineering and scientific community relied on a large, centralized mainframe or a supercomputer to do computational work. A large number of individuals and groups needed to pool their financial resources to afford such a machine. Users had to wait for their turn on the mainframe, and they had a limited amount of time allocated. While this environment was inconvenient for users, the utilization of the mainframe was high; it was busy nearly all the time.
As computers became smaller, faster, and cheaper, users moved away from centralized mainframes and purchased personal desktop workstations and PCs. An individual or small group could afford a computing resource that was available whenever they wanted it. The personal computer is slower than the large centralized machine, but it provides exclusive access. Now, instead of one giant computer for a large institution, there may be hundreds or thousands of personal computers. This is an environment of distributed ownership, where individuals throughout an organization own their own resources. The total computational power of the institution as a whole may rise dramatically as the result of such a change, but because of distributed ownership, individuals have not been able to capitalize on the institutional growth of computing power. And, while distributed ownership is more convenient for the users, the utilization of the computing power is lower. Many personal desktop machines sit idle for very long periods of time while their owners are busy doing other things (such as being away at lunch, in meetings, or at home sleeping).