## Invitation to Computer Science 8th Edition

Published by Cengage Learning

# Chapter 5 - 5.2 - The Components of a Computer System - Practice Problems - Page 238: 3

#### Answer

The instructions that are fetched from memory are usually much larger than $8$ bits in size, often $16$ or $32$ bits. If the $MDR$ were only $8$ bits, then to fetch a $16-$ bit instruction we would have to go back to memory twice. If the instruction was $32$ bits, then we would have to go back to memory four separate times. This would greatly slow down the fetch phase of the instruction cycle. The $MDR$ should be at least as large as the largest instruction that we fetch.

#### Work Step by Step

The instructions that are fetched from memory are usually much larger than $8$ bits in size, often $16$ or $32$ bits. If the $MDR$ were only $8$ bits, then to fetch a $16-$ bit instruction we would have to go back to memory twice. If the instruction was $32$ bits, then we would have to go back to memory four separate times. This would greatly slow down the fetch phase of the instruction cycle. The $MDR$ should be at least as large as the largest instruction that we fetch.

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