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Charging Model


This note sets out EPSRC's policy for calculating the notional cost of using the HPCx service, which the service will follow.

Allocation Unit

All charging calculations will be in terms of a standard Allocation Unit of CPU time, which will be constant throughout the service. The Allocation Unit (AU) can be thought of as a unit of computational work, equivalent to a 1 gigaflops processor running for 1 hour, as assessed by the Linpack benchmark (Rmax). Thus, a 6000 Gflops computer provides 6000 AUs per hour.

The same AU is will used to measure CPU time in grant applications, in the HPCx administrative website and on the system itself, throughout the service. However, because the processors will change as the system is upgraded, the relationship between the AU and the CPU hour will also change.


The charge for the use of every aspect of the service will be calculated on the basis of the number of AUs used. It is assumed that 80% of the total AUs are in fact deliverable; this excludes unused time, and time which is unavailable as a result of failures, scheduled maintenance, etc. This means that the entire cost of the service is divided over this 80% of the AUs.

The cost of the service over Phase 1 and Phase 2 was £734108.43 per month. The Phase 2A upgrade was an additional cost of the service; for that reason, the cost over Phase 2A and Phase 3 will be £752,695.49 per month.

We assume the following:


The HPCx service will be delivered in Phases of increasing power, as shown below.

Phase Start date AUs per hour Total AUs
per month
Deliverable AUs
(80%) per month
cost per AU
1 December 2002 3241 2,367,551 1,894,041 £0.38759
2 June 2004 6188 4,520,334 3,616,267 £0.203
2A November 2005 7395 5,402,048 4,321,638 £0.17417
3 November 2006 12290
8,977,845 7,182,276 £0.10480

The AUs per hour figure at Phase 2A is that registered by Top500 Supercomputer Sites. The figure for Phase 3 is that obtained during the acceptance tests.

AUs and CPU hours

The table shows the relationship between the AU and the CPU hour for Phases 1, 2 and 2A.

Phase AUs per hour Processors 1 AU= 1 CPU hour=
1 3241 1280 0.3949 CPU hours 2.5320 AUs
2 6188 1600 0.25856 CPU hours 3.8675 AUs
2A 7395 1536 0.20771 CPU hours 4.81445 AUs

Although the output of the processors in Phase 3 is in fact slightly higher than in Phase 2A, it has been decided to retain the same relationship between the AU and the CPU hour for time accounting purposes.

February 2007

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