## Invitation to Computer Science 8th Edition

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.
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.