After a recent memory upgrade, a customer is reporting they have seen no improvement in their system performance. Upon inspection, the technician finds that 6.0 GB are detected but only 3.0 GB of memory are usable. Which of the following is the MOST likely cause?
A. The remaining memory is a different type and cannot be used.
B. The remaining memory is defective and needs to be replaced.
C. The customer is using a 32-bit operating system.
D. The memory has not been properly configured in BIOS.