There is a LOT of confusion on Software vs. Hardware RAID. This is my understanding.
Hardware RAID means that virtually all of the work in operating the RAID array is done with a set of dedicated hardware on its own card (including the software in that card's BIOS). The RAID controller card has a Processor, its own RAM, its own BIOS, and its own HDD controllers. All of these components are specifically designed for this purpose and hence optimized for high-speed processing of this type. No matter which type of RAID array it is managing, the system's device manager in the OS (e.g., Windows) basically just passes the data and service requests to the card, and lets the card to all the work.
Be AWARE that there is another sub-set of "Hardware RAID" that is not the same. True hardware RAID has all the hardware needed for the job on the add-in card. But there is a variation of add-in cards that are much cheaper. They include on the card a set of software in a chip, some RAM to be used as buffers, and HDD controller chips. But they don't include a major processor or a lot of RAM. They actually turn over much of the processing work to the computer's main CPU and RAM resources, and only handle the HDD access part themselves. Thus they only reduce the main CPU's work partly, but they are cheaper than full Hardware RAID systems.
Software RAID comes in two main sub-categories. NEITHER of them has its own dedicated hardware for most of the job, and depends almost entirely on main system resources to do the work.
The "built-in RAID" on a mobo is still a Software RAID. Its software is stored in the mobo's BIOS. In most cases when it is used, the software actually is copied at boot time into a spot in RAM used a little like a dedicated cache, just so access to the software is faster than a EEPROM chip can deliver. The RAID management "device driver" in the OS calls on this software to do the work. The work actually is done by the system resources - CPU, RAM, HDD controllers. Thus this method consumes some system resources and slows down overall system performance a bit.
Another version of Software RAID is any software utility package that can be stored on a HDD (or similar) and used as a background application to do the work. The RAID system included with Windows is an example of this. Again the system software will be loaded into RAM for easy quick access, and the system's "device driver" will call on that to do the work. Again the system uses main resources and has a small impact on overall system performance.
Pro's and Con's of those three main types? The main factor in this is that there is NO "Standard" way to do any RAID. Each supplier of systems can do a lot of stuff in their own unique manner, and you can NOT expect two different systems to put the data onto a HDD or retrieve it in the same way. Hence, often data on a HDD array written by one system cannot be read by another.
1. Hardware RAID. Everything on such a system can be unique. The way the data are organized, the nature and details of the management files, the utility tools used for management, etc. If your hardware RAID card fails, your best bet is to contact the maker of that system and ask what current equipment they can provide that WILL be able to deal properly with what's already on your disks. For this reason, one really needs to examine the history and reliability of the card maker, and judge how likely they will be available in ten years, or whatever. Another factor is cost - buying and installing true Hardware RAID is not cheap. The advantages of these systems mainly is speed (and maybe, size of large systems they can handle). Speed two ways - their own cards are faster and more efficient that the computer's main resources at this tasks, AND the main system is free to do other things while the card handles the storage tasks. NOTE that the cheaper "Hardware RAID" systems that do not actually provide all the resources on their own card (and thus hand off significant work to the computer's main CPU) offer less advantage in this processing speed area.
2. Software RAID "built in" on the mobo. Nothing especially unique about the hardware, but the data details written to the HDD's in the array are still unique. If the mobo fails, replacing it means that you also are replacing the software that ran your old RAID system. That CAN mean that the new system cannot use the data on your drives. BUT many mobo makers and their BIOS writers have recognized this and offered a partial solution. Some of them guarantee that, in future versions of the RAID software they include for the HDD controller chips they use on the mobo, they will always make the new RAID software able to use old drives if they still use HDD controller chips by the same maker. So, IF you replace the mobo but ensure that the new one uses HDD controllers from the SAME chip maker as on the old mobo, your old HDD's will still be usable with the new RAID system. Personally I had one experience of this type and it worked perfectly. The main advantage of mobo-included software RAID is cost to the user - almost nothing! If you take advantage of the assurances of future compatibility if you have to switch motherboards, that factor can be a plus that really helps.
3. Software RAID by a separate utility (including Windows' own software RAID) has the big advantage that it can always be replaced by another copy of the same thing, so future changes are much less a concern. In the case of what Windows already includes, the cost is definitely zero; for third-party utilities, maybe more. Some of these may not have all the features or all the handy utility tools needed for management of the system, particularly for handling RAID array failures. And, like other software RAID systems, they consume a small portion of main system resources.
Finally, for software RAID only - this pretty much does NOT apply to true hardware RAID systems - there are utility software tools available - some of them freeware - that claim to know how to read (and hence recover data) from anyone else's software RAID disks. So in the event of a failure that eliminates your original software system without damaging the data on the disks, you MAY be able to get your data this way, even if you can't get a new RAID software package that uses your old disks correctly.
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