To grasp how much data is in the Archive, if it were printed out as a single line of text, it would stretch around the world more than 250 times. Printing it out on pages of A4 would produce a stack of paper two-and-a-half times as high as Mount Everest.

Each entry is a piece of genetic information averaging 864 characters long. Scientists can search these sequences and piece them together to build up the whole genetic information of organisms - mice, fish, flies, bacteria and, of course, humans.

The Archive is 22 Terabytes in size and doubling every ten months - perhaps the largest single scientific database in Europe, if not the world.

Martin Widlake, Database Services Manager at the Wellcome Trust Sanger Institute said: "At 22 000 GB the Trace Archive is in the Top Ten UNIX databases in the world. That's not bad for a research organisation of 850 employees in the countryside just outside Cambridge."

"It is possibly the biggest single (acknowledged) scientific RDBMS database in Europe, if not the world."

All the data are freely available to the world scientific community (http://trace.ensembl.org/), as a resource to geneticists all over the globe. When a researcher is studying a disease or gene, they can download the genetic information known about the area they are studying.

The data are being actively used by biomedical researchers in academic and commercial organizations. The three internet domains that make most use of the trace archive are .com, .edu and .uk. Dotcoms are responsible for about 80% of download each week - mostly as big 'customers', taking vast chunks each visit. Next are US university researchers, followed by UK scientists.

Trace data are the raw results of genetic research to allow them to identify and study genes, to reveal variations (mutations) in genes and to study similarity to genes in other organisms. These are vital starting points for studying and better understanding the biology of health and disease.

By any comparison, the billion records stands above many other familiar repositories. The British Library holds 13 million items: the US Library of Congress holds 115 million items. The Trace Archive holds one billion chunks of unique information.

"Accessing the data becomes a larger and larger problem as the dataset grows," continued Martin Widlake. "At present it is simple and very quick to access a record if you know its unique identifier as issued by the Sanger Institute, the US National Center for Biotechnology Information (NCBI) database, or the 'name' of the trace as given by the organization that originally sequenced that piece of genetic information."

"Scanning the whole dataset for a single genetic sequence, which is a lot like searching for a single sentence in the contents of the British Library, is a massive task. However, the team at the Sanger Institute are working on new methods to make the data easier to search and access".

The data are held in duplicate, with the NCBI also maintaining a copy: with two sites holding it, a single disaster cannot wipe out the only copy of this vital and heavily used database.

Note: If no author is given, the source is cited instead.

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• Encryption

• Human Genome Project
• Computational genomics
• GenBank
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• Human genome
• Genetics