The comPOUND module is extremely compact (1.2m x 1.65m x 2.4m). Storing 100,000 samples in such a small unit  requires a completely new method of storage. Conventional tray and shelving arrangements or paternosters would have required redundant space in order to give a manipulator arm access to each tube. comPOUND avoids this by storing tubes in concentric circles of holes in a moulded plastic carousel - each carousel is capable of holding over 3,800 tubes. 

Twenty six carousels are mounted one above the other on a shaft with a minimal gap between them to give the 100,000 sample capacity (up to 200,000 for the double-density module).

Retrieval also required a totally new approach. 

comPOUND does not use robotic arms but instead sends samples to, and retrieves them from, storage using air pressure. As well as storage holes, each concentric row of every carousel has a delivery hole. Retrieval of a tube simply involves selecting the carousel with the target tube, and rotating it so that the target tube is in line with the delivery holes in all of the other 25 carousels. Compressed air then pushes out sleeves within each delivery hole, forming a temporary pipe through the carousels. When a burst of compressed air is applied at the bottom of the temporary pipe, the sample tube is lifted to the turntable at top of the machine. The turntable acts as a gas interchange with the outside air and also collates tubes from all radial locations to a single output tube.

At the front of the comPOUND unit, an indexer arrays the delivered tubes into a standard 96-way SBS rack. To return tubes to the store, the same process is followed in reverse.

In order to ensure that tube identity and selection is correct, comPOUND uses a 2D barcode (10 digit number with error-checking and error-correcting bits) on the base of each storage tube. The barcode is read both upon entry to and exit from the comPOUND unit.

The comPOUND cabinet temperature can be adjusted from ambient down to –20°C. To keep samples dry, the cabinet is purged with dry air or nitrogen. One of comPOUND’s great advantages is that that nearly all of the electrical components are outside the controlled environment storage cabinet, minimising temperature fluctuations and increasing reliability of the components.