To create a file in one of the new ‘big’ formats, users start with a BED, BedGraph, or Wiggle text file and then run a conversion program on their own machine to convert the text file to the corresponding binary format. Executable versions of the conversion programs, called bedToBigBed, bedGraphToBigWig and wigToBigWig, are available on the Genome Browser downloads server (http://hgdownload.cse.ucsc.edu/admin/exe/), along with several programs to aid in working with the new binary data file types. Once a bigBed or bigWig file is viewed as a custom track, the uploaded data remains cached at UCSC for at least 48 h from last use without any additional data transfer. The life of the cached data can be extended by creating a session (9) that includes the ‘big’ custom track.
