The E 791 Parallel Architecture Data Acquisition System

To collect data for the study of charm particle decays, we built a high speed data acquisition system for use with the E791 magnetic spectrometer at Fermilab. The DA system read out 24 000 channels in 50 μs. Events were accepted at the rate of 9 000 per second. Eight large FIFOs were used to buffer event segments, which were then compressed and formatted by 54 processors housed in 6 VME crates. Data was written continuously to 42 Exabyte tape drives at the rate of 9.6 Mb/s. During the 1991 fixed target run at Fermilab, 20 billion physics events were recorded on 24 000 8 mm tapes; this 50 Tb (Terabyte) data set is now being analyzed. ∗Now at the Universidade Estadual do Rio de Janeiro, RJ, Brasil.