A circle $A$ is circumscribed about a unit square and a circle $B$ is inscribed inside the same unit square. Compute the ratio of the area of $A$ to the area of $B$.
1. **Determine the radius of circle \( B \):**
   - Circle \( B \) is inscribed inside the unit square.
   - The side length of the unit square is 1.
   - The radius of circle \( B \) is half the side length of the square.
   \[
   r_B = \frac{1}{2}
   \]
   - The area of circle \( B \) is:
   \[
   \text{Area}_B = \pi \left( \frac{1}{2} \right)^2 = \pi \cdot \frac{1}{4} = \frac{\pi}{4}
   \]

2. **Determine the radius of circle \( A \):**
   - Circle \( A \) is circumscribed about the unit square.
   - The diagonal of the unit square can be found using the Pythagorean theorem:
   \[
   \text{Diagonal} = \sqrt{1^2 + 1^2} = \sqrt{2}
   \]
   - The radius of circle \( A \) is half the diagonal length of the square.
   \[
   r_A = \frac{\sqrt{2}}{2}
   \]
   - The area of circle \( A \) is:
   \[
   \text{Area}_A = \pi \left( \frac{\sqrt{2}}{2} \right)^2 = \pi \cdot \frac{2}{4} = \frac{\pi}{2}
   \]

3. **Compute the ratio of the area of circle \( A \) to the area of circle \( B \):**
   \[
   \text{Ratio} = \frac{\text{Area}_A}{\text{Area}_B} = \frac{\frac{\pi}{2}}{\frac{\pi}{4}} = \frac{\pi}{2} \cdot \frac{4}{\pi} = 2
   \]

The final answer is \(\boxed{2}\)