Question

consider a 64bit microprocessor with a 32-bit external databus, driven by a 120-mhz input clock. assume that this microprocessor has a bus cycle whose minimum duration equals three input clock cycles. What is the maximum data transfer rate across the bus that this microprocessor can sustain in bytes

Answer 1

Given:

Microprocessor = 64-bit

External Data Bus = 32-bit

Input clock = 120 MHz

1 Bus cycle = 3 Input clock cycles

To find: Maximum data transfer rate.

Solution: Clock cycle = 1/ Frequency = 1/(120 MHz) = (1/120 × 10⁶) s = 8.33 ns

1 bus cycle = 3 × clock cycles = 3×(1/(120×10⁶))s = 3/(120×10⁶)s = 25ns

Data transfer rate per bus cycle = 32-bits = 4bytes ( => 4bytes are transferred for every 25ns)

Maximum bus cycle rate = 120 MHz/3 = 60 M/s

(Notice in the above step the change in units, the change in units happen as a result of the formula frequency=1/time. Here, MHz changes to M/s.)

Therefore,

Maximum data transfer rate = (Bus cycle rate) × (Data transferred per bus cycle) = 60M × 4bytes = 240 Mbytes/s = 240 Megabytes/s.