Question

If a cache has 64-bytes cache lines, how long does it takes to fetch a cache line if the main memory takes 20 cycles to respond to each memory request and returns 2 bytes of data in response to each request ?

• A. 640 cycles
• B. 160 cycles
• C. 320 cycles
• D. 980 cycles

Answer 1

The correct option is A 640 cycles

option (b)

In one request, 2 Bytes of data can be accessed from main memory. Number of request needed to access a cache line of size

$64B=\frac{64B}{2B}=32$

1 request time = 20cycles

$\text{32 requests time}=32\times 20$

$=640cycles$