Memory bandwidth is usually expressed in units of bytes/second, though this can vary for systems with natural data sizes that are not a multiple of the commonly used 8-bit bytes.
These are intended to provide insight into the memory bandwidth that a system should sustain on various classes of real applications.
Some personal computers and most modern graphics cards use more than two memory interfaces (e.g., four for Intel's LGA 2011 platform and the NVIDIA GeForce GTX 980).
High-performance graphics cards running many interfaces in parallel can attain very high total memory bus width (e.g., 384 bits in the NVIDIA GeForce GTX TITAN and 512 bits in the AMD Radeon R9 290X using six and eight 64-bit interfaces respectively).
In systems with error-correcting memory (ECC), the additional width of the interfaces (typically 72 rather than 64 bits) is not counted in bandwidth specifications because the extra bits are unavailable to store user data.