Online Computer Farm

The role of the online computer farm [89] is to format an event data into an off-line event format and to proceed background reduction (the Level 3 trigger) using a fast tracking program [90]. Fig.  shows the architecture of the online farm. The farm consists of six VME crates. Each VME crate contains a Power-PC based control processor, Motorola MVME-2604, and 16 MC88100 event processors in four VME modules, Motorola MVME-188s. The interfaces for the event builder and the mass storage system are also implemented in each crate.

Figure: The online computer farm, that consists of six VME crates of processors. Also shown is the data monitoring system using an external Linux-SMP PC server for data quality monitoring.

In each crate, data from the event builder interface are distributed to 16 event processors through the VME backplane, and the event formatting and background reduction are performed in parallel. The processed data are then sent to the mass storage interface. The throughput of a crate is 2.8 MB/sec which corresponds to more than a 15 MB/sec transfer rate with all the six crates. The software for the online farm can be developed on a host workstation which has the off-line software development environment and the executable image developed on the workstation can be directly downloaded to the online farm.