Computers as Components, 2nd Edition

194 CHAPTER 4 Bus-Based Computer Systems

t ⫽ T

basic

· P ⫽ 1,224,000 · 1 ⫻ 10

⫺6

⫽ 1.224 sec. (4.6)

Since the total time to transfer one second’s worth of frames is more than 1 s, the bus is not

fast enough for our application.

The memory provides a burst mode with B ⫽ 4 but is only 4 bits wide, giving W ⫽ 0.5.

For this memory, D ⫽ 1 and O ⫽ 4. The clock period for this memory is 10

⫺7

s. Then

T

mem

⫽ (4 · 1 ⫹ 4)

612,000

4 · 0.5

⫽ 2,448,000 cycles, (4.7)

t ⫽ T

mem

· P ⫽ 2,448,000 · 1 ⫻ 10

⫺7

⫽ 0.2448 sec (4.8)

The memory requires ⬍1 s to transfer the 30 frames that must be transmitted in 1 s, so it

is fast enough.

One way to explore design trade-offs is to build a