The present invention is directed toward a texture combine circuit for generating fragment graphics data for a pixel in a graphics processing system. Said training cartridge has a central channel running therethrough which accommodates a propellant charge in the rear area of the cartridge and is closed at the rear by a detonator charge for the propellant charge. A parallel or graphics processor can autonomously execute the first set of CTAs and delay execution of the second set of CTAs until the first set of CTAs is complete. A semaphore system can be utilized to indicate which blocks of local memory are availableunavailable. A device for retaining a string of tubulars, the device comprising at least one body part having a curved tapered surface upon which inserts are located for engagement with the string of tubulars characterised in that the curved tapered surface comprises a recess for the passage of cables.