The term supercomputer typically refers to dedicated special-purpose multiprocessor computing system that provides close to best achievable performance for demanding parallel workloads. Supercomputers have several characteristics that enable them to efficiently execute considerable computational loads.

1. High-end and highly reliably hardware components, such as processing units, primary and secondary memory, and interconnects
2. Supercomputer middleware provides a straightforward abstraction of a homogeneous computational and networking environment, automatically allocating resources according to the underlying networking topology
3. The resources of a supercomputer are managed exclusively by a single centralized system, which enforces global resource utilization policies, thus maximizing hardware utilization while minimizing the turnaround time of individual applications.

These characteristics endow supercomputers with unprecedented performance, stability, and dependability properties.

Grid computing systems could be viewed as large-scale computing systems with considerable levels of hardware resources but with a lack of the features that make supercomputers so powerful. In particular, grids usually lack sophisticated support for highly parallel applications with significant inter-process communication requirements. Grid computing environments are based on heterogeneous, widely dispersed and time-variant resources which typically lack central control. Connected via local and wide area networks, grids typically rely on an opportunistic marshaling of resources into coordinated action to meet the needs of large-scale computing applications. Grids are often offered as panacea for all kinds of computing applications, including those that require supercomputing-like computing environments. However, this vision of grids as virtual supercomputers is unattainable without overcoming the performance and reliability issues plaguing current grids.

The main challenge of the QosCosGrid project is to overcome the current limitations of grids and implement a virtual computer which could be considered a viable approximation of a real supercomputer.