The data acquired during a scan are stored in the SCAN_D array. You can see the available space with the command whats:
10.SPEC> whats SCAN_D A global double 4096-row 5-column row-wise array.
There are as many columns as counters are defined in spec plus one extra column to store the position of the motor being scanned. In this example five columns correspond to four counters and one motor.
Initially space for as much as 4096 points is reserved. Nevertheless the standard spec macros will increase this size automatically as the scan will reach that limit.