Data accumulation rate and data size

The total number of channels (ADC, TDC, and scalers) has been summarized in table 23. In order to obtain an upper limit on the data size the following assumptions have been made:

• Both spectrometers see two tracks each within the width of the ADC and TDC gates. Typically the gate width will be 100 ns. It should be noted that on average two tracks will require a sustained single spectrometer event rate of more than 10 MHz.
• TDCs will only be read if they show a valid hit. Therefore, two words have to be stored for each channel, one data word and one address word.
• ADCs will always be read (not sparsified). Therefore, one data word is sufficient per channel.

The table 24, with the assumption of double tracks, lists the number of channels hit in each detector group:

表 24: Number of channels to be recorded.

Detector	ADC	timing TDC	pattern TDC
HDC 1&2	N/A	24	N/A
HTF	88	12	12
HAC	42	N/A	20
HWC	48	N/A	18
EDC	N/A	20	N/A
EHOD	102	10	11
FR	4
BPM	16
total	300	66	61

For unsparsified ADCs, a total of 300 channels or 300 data words has to be read per event. For sparsified TDCs the total number of channels is 127 channels or 254 data words. Therefore, a total of 554 words or 1108 byte would be necessary for one event. A few more words would be needed for event and sub-event headers. As the assumption of double tracks in both spectrometers is a worst case scenario, it should be safe to conclude that the total event size is not significantly larger than 1 kB/event. This roughly equals the size of a HMS-SOS coincidence event. The standard Hall C data acquisition routinely has been read at event rates of 1 kHz and our expected trigger rate is less than 1 kHz (section 3.6). Data accumulation rate of 1 MB/sec (=1kB/event $\times$ 1kHz) is manageable by the standard Hall C DAQ and total data size will be less than 3 TB for 29 days of beamtime including apparatus development runs.

Beam condition and magnet status monitors will also be recorded periodically (once every 10$\sim$30 sec) through EPICS during the beamtime.