It's basically using two or more disk as one, and striping data across them. This allows for reading from two disk at once rather then one, same for writing. It's a good bit more complicated then that in reality and no where close to 2x the performance of a single drive real world, but that's the basis of it.
It's being used less and less now that SSD's are more affordable. 2x WD Raptors in Raid 0 was fairly common for gaming machines not to long ago, but no one really bothers with that anymore since SSD's perform so much better.
Reasonably well-educated opinion: it is _not_ better, and it is _not_ worth doing.
"RAID 0" is not actually RAID. The R stands for Redundant, and the idea of RAID was not only to speed things up by spreading IO over multiple drives but to survive the loss of one or more drives. In zero, lose one and you've lost the whole array. Do backups often.
Zero does improve serial transfers; Tom's did a project of building a large enough array to get 3 GBytes per second. SATA is 3 GBits per second, so this is eight times the throughput.
However, it does not scale as well on SSDs as it does for HDDs. With HDDs, in random read patterns seek time is dominant, and one drive could be transferring while another was seeking. SSDs seek so quickly that they do not scale up as well as HDDs do. They do scale up, but not as well.
Generic advice (I should save this in a file so I can just re-post it): Unless you are trying to solve a _specific_ need that RAID0 will address, or doing benchmarks for the fun of it (I used to do that), avoid RAID0. It introduces complication and risk, and the benefit is, in most cases, questionable. If you do need RAID for things like video capture or editing, consider investing in more drives and using RAID 5, 6, or 0+1 so that a single failed spindle will not wipe out all of your data.
Raid0 - Prior to SSDs I used raid0 on ALL of my builds. No longer use.
Raid0 improves Sequencial read/writes, But does not improve access time and very little preformance gain for random 4K read/writes. For the operating system and programs Raid0 does little to improve performance as Sequecial performance is the LEAST important matrix, It's access time and small 4k random performance that is important. Raid0 for HDDs does improve read/write performance when working with large files that are Sequencial - ie a 1 gig dot vob file will consist of 250 K clusters, a large photo jpeg may be up to 2500 sequencial clusters. So if you do a lot of vedio encoding or work with (often) large jpeg photoes, then Raid0 makes sense.
For SSDs(When SSD is a member drive of a Raid setup)a negative is that windows 7 Trim command is not allowed (currently). This means that the SSD must rely soley on it's internal garbage collection (CG) to maintain performance. CG works, but not the greatest. Due to the Cost of SSDs they are normally used solely for the OS + programs and benifit VERY little from raid 0. For the majority a 2 disk SSD, Not in raid0, is a good option. One for OS + programs and one for a scratch/work disk.
The best setup, if Working with LARGE file structures, is a 3 disk setup. One SSD for OS + Program and two HDD in a raid0 setup for your data.
^ You are correct trim is limited to Windows 7, No trim for Prior windows operating system - including no support in vista.
While CG has improved, depending on user and how CG is employed, a SSD may experience slow downs. I think ALL newer SSDs employ some form of CG, The CG in some of the SSDs (ie Marvel based Sata III) only works when the SSD is in Idle mode and some users have indicated that they have had to "log" off and leave the drive sit idle for a considerable period of time to restore the "factory fresh" performance.
If you follow some of the previews on anadtech for SSDs, this is noted as a negative.
^ Nice, and so true.
RAID 0 is not "better", as most people who ever set it up and actually use it, will find out after a period of time. It can be fun, and it can bring enhancements for large file transfer situations, but beyond that, it was a solution for days gone by when the norm was 512 meg of memory and ATA33 speed drives. With drives being painfully slow years ago, and the max onboard memory be relatively limited by either hardware constraints, or RAM that cost $100 a megabyte, we did anything we could to speed up moving information on our drives. With the much, much faster SATA drives today, huge amounts of cheap memory onboard, and especially the coming of SSD's, RAID 0 is pretty much an antiquated novelty.
People do RAID SSD,s though there really is no reason. Most people, including gamers, don't need to move large amounts of data quickly, they need sequential reads that happen very quickly for relatively small amounts of data, which an SSD does almost instantly. Seek times are very nearly non-existent. That is what the Raptors were good for, they had very low seek times and much faster sequential reads than an average drive. People RAID'd Raptors because, well, quite frankly the larger Raptors were very expensive. You could buy 2 smaller ones cheaper than 1 large Raptor, and get the same storage space as well as the benefit of increased overall throughput. Putting SSD's into RAID 0 has questionable benefits, it will increase overall data throughput, but with through put of an average SSD being 450 MB per second, how much more do you really need?
Then last but not least, striping your data across a couple of drives is a recipe for disaster. Most people find that its not the drives failing that is the worry, its gamers playing with their machines, overclocking, etc. that inadvertently for whatever reason they break the array. (having to reset the BIOS for instance will undo your RAID array) and before they understand fully the problem they have created and the fix, they damage the data in the array, rendering the array unrepairable and they lose everything they had on the drives.