CCD data are taken and stored with the Data Acquisition System, which provides a large range of commands for taking data of various types, and storing the data with or without the header information in various forms on the VAX discs. A description of the system, together with a complete list of the commands, is given in ``William Herschel Telescope Instrument control and data acquisition system user manual'', by S.W. Unger & G.T. Rixon, and only a subset of the commands, relevant to observing with CCDs at Prime Focus, are listed here. Many commands do almost identical things, for instance the commands RUN, FLAT, and SKY differ only in one header item in the data file. The commands SCRATCH and PROMOTE are intended for use by automatic setup procedures yet to be written.