If the average time to handle a page fault is 10 milliseconds, and a memory access requires 1 microsecond, then achieving a 99.99% hit ratio would lead to an average memory access time ofa.1 millisecondb.1.9999 millisecondsc.1.9999 microsecondsd.9.999 microseconds

To determine the average memory access time given the hit ratio, we need to use the following formula:

$\text{Average Memory Access Time} = (\text{Hit Ratio} \times \text{Memory Access Time}) + (\text{Miss Ratio} \times \text{Page Fault Time})$

Given:

• Hit Ratio = 99.99% = 0.9999
• Miss Ratio = 1 - Hit Ratio = 1 - 0.9999 = 0.0001
• Memory Access Time = 1 microsecond = 1 $\mu$s
• Page Fault Time = 10 milliseconds = 10,000 microseconds = 10,000 $\mu$s

Now, plug these values into the formula:

$\text{Average Memory Access Time} = (0.9999 \times 1 \mu\text{s}) + (0.0001 \times 10,000 \mu\text{s})$

Calculate each part:

1. $0.9999 \times 1 \mu\text{s} = 0.9999 \mu\text{s}$
2. $0.0001 \times 10,000 \mu\text{s} = 1 \mu\text{s}$

Add these two results together:

$\text{Average Memory Access Time} = 0.9999 \mu\text{s} + 1 \mu\text{s} = 1.9999 \mu\text{s}$

Therefore, the average memory access time is:

$\boxed{1.9999 \text{ microseconds}}$

So, the correct answer is:

c. 1.9999 microseconds