There seems to be a considerable level of confusion about what's the difference between bump, displacement and normal maps, and even some dispute about which is better. People ask me about this so often that I have decided to make the whole nine yards clear in one place. Let's cover all 3 kinds of maps right here! But before I cover each in detail, let's remember that they all serve the same purpose, but in different ways. ^___^
Let's start with the simplest first. Bump maps are 8-bit greyscale maps that add bumpiness to 3D surfaces. And by 8-bits, I mean the greyscale maps can only use up to 256 levels of grey, which limits the smoothness of the results. But wait, there is more - bump maps can only represent bumps in a single direction, perpendicular to the surface. In other words, in the direction of the surface normal vector. This is like up and down only.
In addition to these limitations, bump maps do not really change the geometry shape. It instead fakes it by means of mathematically changing the face's normal vectors to cause fake shadows that simulate the presence of bumps. So the effect depends on lighting directions, and cannot be seen from outlines of the 3D model. So even if the model may appear to have bumps, its silhouette will remain perfectly smooth. It can fool the eyes in one way, but not the other. The math to calculate the normal face vector direction has some level of impact on rendering times.
Displacement maps work in a completely different way. They actually displace the geometry (hence the name) to create physical bumps instead of faking their shadows. What kind of geometry can be displaced depends if the rendering engine supports (or not) microface displacement. If it does, even a single face can be greatly detailed with a displacement map, even if it doesn't have the sufficient geometry to do it. If it doesn't, the geometry will require a lot of additional faces to be able to produce the level of detail required by the displacement map. In general, displacement maps require considerable computer power to process, so they impact rendering performance considerably.
Now let's cover normal maps. These are the newest technology in the bunch, and again, works in a completely different way. There are basically 3 types of normal map: object space, tangent space, and MikkT space. Older rendering engines such as Firefly and 3Dlight use old school tangent space, and Poser also supports object space. Which one to use depends on what you want the model to perform.
Object space is used on static models that don't bend or deform, like 3D props. Now tangent space is used on organic models that bend and deform, like bone-rigged characters. So far, so good, but tangent space has issues when dealing with mirrored geometries, like the other side of a shoe/boot, the other hand of gloves, or the other side of the body. It will display the effects of the normal map inverted on the mirrored side, and there is nothing you can do about it.
On a practical side, normal maps are also fake detailing like bump maps, but they have 2 major advantages. First, it can use millions of levels as opposed to only 256 from bump maps, which create much smoother results. Secondly, it can represent displacement in all 3 directions (x, y, and z), which can produce much more detailed results than bump. It does that by storing pre-calculated 3D vectors info encoded into the RGB color space of a bitmap file, so the results of all the calculations are already stored and ready to use, like a LUT (look-up table).
This makes normal maps much faster and efficient than bump maps, and that's the reason they are the option of choice in real-time game engines. They render faster, the results are smoother and more detailed. But they are still fake details, so the details won't show in the model's silhouette. Like bump maps, the effects can only be seen from certain angles, and depend on the scene lighting.
Now back to the issues with old tangent space, modern rendering engines like Octane, Iray and Cycles use a new normal space mapping called MikkT, which is the modern standard. It automatically compensates for mirrored surfaces, and displays the results correctly. Firefly and 3Delight don't support, and will never support MikkT for backwards compatibility reasons. That would fix the mirrored geometry issues, but would break everything that was already made for the older version, so it's a no-win in either cases.
The problem is having 2 rendering engines in both Poser and DS, where one supports only tangent space and the other MikkT, which causes a compatibility issue with normal maps. You can't make a material that will work properly in both. The green RGB channel in MikkT maps are inverted comparing to the same map using tangent space, and tangent space cannot handle mirrored geometries, while MikkT can.
We can use shader nodes in Poser to invert the green channel and reuse a tangent space normal map in Cycles, and perhaps do the same in DS using ShaderMixer bricks. The important is to know that these differences exist, and where. But the fact is that normal maps are way more modern, efficient, and versatile comparing to bump maps. Displacement is the only of the 3 that actually creates new geometry, while bump and normal fake it. Nonetheless, displacement is the most computationally expensive of the bunch, so it's the slowest to render.
Normal maps, conversely, are so fast to render that many programs can show their full effect in real time, like Poser previews when hardware OpenGL acceleration is enabled, assuming your video card supports that. All modern game engines support displaying normal maps in real-time. As seen above, there are indeed some compatibility issues, but it's still the best option performance-wise.
Although displacement maps are the slowest from the bunch, modern nVidia video cards that support DirectX 11 can use the massively parallel power of the GPU to hardware accelerate displacement in real-time using micro-displacement. A few AAA video games take advantage of this, and it can make a huge difference in the final visuals. It can take a single face and detail it to your heart's content using real displacement instead of fake bump or normal maps.
So these are the options, how they work, and what they do. There are some pros and cons for each one, and many rendering engines support using both bump and normal maps at the same time (like Firefly), affecting the same geometry.
Hope this helps clearing out the confusion regarding these maps, and help you make your choice next time you need them.