Memory bandwidth ($B=Q/T$)

Memory bandwidth is the rate at which data crosses a specified computer memory interface, commonly measured in bytes per second. If $Q$ bytes are transferred in time $T$, the measured average is $B=Q/T$. The interface and counting convention matter: an application-level count can differ from physical traffic caused by memory caches.

A streaming array operation reading two eight-byte values and writing one per element transfers at least 24 useful bytes per element. At a sustained $24\times 10^9$ bytes per second, that traffic alone limits throughput to $10^9$ elements per second. Memory access latency instead measures how long one access takes. Overlapping many accesses can achieve high memory bandwidth despite substantial memory access latency. STREAM measures sustained memory bandwidth with simple array kernels and working sets larger than the available memory cache.^[ref]