Memory

Problem:

How long does it take to get 4 bytes?

If the data is word-aligned, and it takes time T to get 1 byte, it will take time 4T

to get 4 bytes (4 accesses to the same chip)

Why is word alignment significant?

Solution: put consecutive bytes on different chips. This is called interleaving.

M[0] on Chip 00, M[1] on Chip 01, M[2] on Chip 10, M[3] on Chip 11,

and M[4] back on Chip 00

If data is word-aligned, first byte always appears on chip 00

Also, the other bytes are at the same address on the other chips

Allows accessing an entire word in time T

Where is M[5]? Chip 01, index 1

In general, where is M[i]? Think of the address in binary.

The chip is at i % 4

The chip is the low two bits.

The index is at i / 4

The index is bits B11-2.