The NA48 Data Acquisition PC Farm


The NA48 Experiment at CERN has installed a PC farm for data acquisition and event-building in the 1998 run period.
Each subdetector in the experiment is connected to a SubDetector PC (SDPC) and dumps all its data into this PC during the SPS (Super Proton Synchrotron)  burst (2.5s every 14.4s).  Each data stream consists of a sequence of event fragments generated by the respective subdetector.

Between bursts, each SDPC sends a fraction of its event fragments across a Fast Ethernet switch to each of several Event-Building PCs (EBPC). The EBPCs combine all the event fragments belonging to one event and write the completed events to a local disk buffer. In that way each EBPC generates a burst fragment ("burstlet") file per SPS burst.

The burst fragment files are then picked up by the Central Data Recording (CDR)  mechanism and sent to the  CS-2  in the CERN computer centre where they are assembled to complete burst files, processed by the level-3 trigger, reconstructed and written to permanent tape storage.

In the current configuration of the readout systems each SPS burst generates ca. 270-280 MByte of data, this corresponds to a continuous data rate of  18-20 MByte/s ( 1.1-1.2 Gbyte/min)

A sketch of the NA48 data acquisition system is shown below.

Click on image to get expanded version

The Components

Subdetector to PC links

Subdetector PCs (SDPCs)

The PCs connected to the subdetectors are standard PentiumII-266 systems equipped with 128MByte RAM, a DT16 interface and a 100MBit/s Ethernet card.

Event Building PCs (EBPCs)

Each Event-Building PC is equipped with 2 PII-266 processors, it has 192MByte RAM, 4 x 4.5GByte SCSI harddisks and a 100Mbit/s Ethernet card.

CDR Routing PCs (CDRPCs)

To fulfill the requirement of compatibility with the old data acquisision system based on 4 DEC Alpha TurboChannel Workstations with FDDI interfaces, we are using the 4 CDR Routing PCs as protocol converters between Ethernet and FDDI. Each CDRPC has 64MByte RAM, an FDDI interface and a 100MBit/s Ethernet card and acts a an IP router. The CDRPCs will become obsolete as soon as the direct Gigabit Ethernet link from the switch to the computer centre has been installed.


Operating System


Installation of the Farm

Experience Installing and Operating the Farm

Some Photos

The PC Farm Team

Additional Documents

Steffen Luitz
21 August 1998