Aptitude [ST Microelectronics Placement]: Sample Questions 26 - 27 of 40

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Question 26


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Short Answer▾

A CPU has four group of instruction set A, B, C, D

CPI of A = 1

CPI of B = 3

CPI of C = 2

CPI of D = 4

The CPU access 20 % of A, 30 % of B, 30 % of C and 20 % of D

What will be the average CPI?


For any particular instruction it is CPI CPU access (%)

Average CPI = + + +

Average CPI = 1 + 3 + 2 + 4


Question 27




In which of the following schemes after page replacement the entered page will enter in same memory location as of replaced one.


Choice (4)




N - set associative


Direct mapping


All of the above




  • Associative mapping: In this type of mapping the associative memory is used to store content and addresses both of the memory word. This enables the replacement of the any word at any place in the cache memory. It is considered to be the fastest and the most flexible mapping form.
  • Direct mapping: In direct mapping the RAM is made use of to store data and some is stored in the cache. An address space is split into two parts index field and tag field. The cache is used to store the tag field whereas the rest is stored in the main memory. Direct mapping՚s performance is directly proportional to the Hit ratio.
  • Set - associative mapping: This form of mapping is a modified form of the direct mapping where the disadvantage of direct mapping is removed. Set - associative mapping allows that each word that is present in the cache can have two or more words in the main memory for the same index address.

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