in simultaneous organisation the formula would be something like
T= hit rate*(cache access time) + miss rate* (main memory access time)
Simultaneous AMAT
Tavg = h1 t1+ (1- h1) t2 + (1- h1) (1- h2) t3 .............. (i)
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In hierarchical access we use this formula :
T= hit rate*(cache access time) + miss rate* ( cache access time + main memory access time)
Hierarchical AMAT
Tavg = h1 t1+ (1- h1) h2 (t1+t2) + (1- h1) (1- h2) (t1+t2+t3) ............... (ii)
Both have L1 cache then L2 cache then Main Memory ( means 3 levels of Hierarchy ) .
Though i believe the exact formula depends on which situation we use that particular theory ..