Originally Posted by xpi0t0s View Post
Sometimes I find questions like this easier to work through if I use actual numbers. So let's say there are 100 memory accesses. How many read and how many write will there be (this is easy)? How long will a single read take, if it comes from cache? How long will a single read take if it comes from main memory? How long will a write take? Now add them all up to produce a time for the 100 memory accesses. Then divide by the number of accesses and that should give you the answer you're looking for (for b. a is of course easier than that.)

c also sounds easy, what's the problem? Do you know how to calculate hit ratios? Let's say I'm playing darts and I throw 10 darts and 4 hit the board (that would be doing well for me). What would my hit ratio be? Do you get 0.4?
you are on a right, a is simple. but regarding b isn't.
because in this case ,we should consider write operation too. so, it must be there hit ratio for write as for read,but in question there isn't hit ratio for write .
of course, I know how to calculate hit ratio. it is hit\ miss +hit.
please tell me ,how I can know the no. of hits and no. of misses?
I can't guess what hit ratio as you did with your darts.
I think, the author supposed that mention of hit ration for write it isn't necessary , because the write through policy is depended here.
because of in both miss and hit there is access to memory.
im not sure .
I hope to get more comments from you.