**Main Similarities between HCP and CCP structures:**

1. **Close-Packed Structure:** Both HCP (Hexagonal Close-Packed) and CCP (Cubic Close-Packed) structures are examples of close-packed structures. This means that the constituent particles (atoms, ions, or molecules) are arranged in a closely-packed manner, maximizing the packing efficiency.

2. **Face-Centered Arrangement:** Both HCP and CCP structures have a face-centered arrangement of constituent particles. In other words, each face of the unit cell in these structures is occupied by a particle. This arrangement results in a high coordination number and dense packing.

3. **Equal Packing Efficiency:** Both HCP and CCP structures have the same packing efficiency, which is approximately 74%. This means that about 74% of the total volume of the unit cell is occupied by the constituent particles, while the remaining space is empty.

**Main Differences between HCP and CCP structures:**

1. **Unit Cell Shape:** The key difference between HCP and CCP structures lies in the shape of the unit cell. In HCP, the unit cell is a hexagonal prism, whereas in CCP, the unit cell is a cube.

2. **Number of Particles per Unit Cell:** HCP structure contains 6 particles per unit cell, while CCP structure contains 4 particles per unit cell.

3. **Closest-Packed Planes:** In HCP, the closest-packed planes are the hexagonal planes, while in CCP, the closest-packed planes are the square planes. The arrangement of particles in these planes differs due to the different shapes of the unit cells.

4. **Stacking Sequence:** The stacking sequence of closest-packed planes also differs in HCP and CCP structures. In HCP, the stacking sequence is ABAB..., where A and B represent two different layers of particles. In CCP, the stacking sequence is ABCABC..., where A, B, and C represent three different layers of particles.

5. **Crystal Symmetry:** HCP and CCP structures have different crystal symmetries. HCP structure possesses a hexagonal symmetry, while CCP structure possesses a cubic symmetry.

6. **C/A Ratio:** HCP structure has a C/A ratio, which refers to the ratio of the height (C) to the basal plane length (A), equal to approximately 1.633. CCP structure does not have a C/A ratio since it is a cubic structure.

In summary, HCP and CCP structures share similarities in terms of being close-packed structures with a face-centered arrangement. However, they differ in terms of unit cell shape, number of particles per unit cell, closest-packed planes, stacking sequence, crystal symmetry, and the presence of a C/A ratio.

Both types of close packing ccp and hcp are equally efficient and have same packing efficiency of 74%.