Abstract: A programmable device, such as a field programmable gate array, includes at least one signature bit that is used to indicate whether the programmable device has fewer than all the logic blocks accessible to the user. The signature bit may be programmed after the manufacture of the programmable device or may be hard wired during the manufacture of the device. The programming unit recognizes the configuration of the signature bit and restricts access to particular logic blocks based on the configuration. Thus, a large programmable unit may become a smaller “virtual” programmable device by altering the configuration of the signature bit, which is recognized by the programming unit. Consequently, the manufacturer may test market programmable devices of differing sizes to determine demand without incurring the costs associated with producing a completely new product line.