What are the differences between DVD-R / RW, DVD+R / RW and DVD-RAM?

There are 3 main streams :         
DVD-R / RW : leads by Pioneer and Sharp         
DVD+R / RW : leads by Sony, Philips and HP         
DVD-RAM : leads by Panasonic, Toshiba and Hitachi

DVD-RAM
DVD-RAM uses Zone Constant Linear Velocity ( also known as Z-CLV ) for reading. It divides the disc into several districts and arranges in a spiral way. Each district contains several sectors. Each sector has its own physical address. Therefore, it uses the same " Data Random Storage " as HDD, which also provides burning repetition.        
DVD-R / RW
Its burning principle is similar to CD-R / RW, which uses Constant Linear Velocity (also known as CLV). A DVD-R can only be burned once. But DVD-RW uses " Phase Change " burning technology; therefore, it can be re-burned.        
DVD+R / RW
DVD+R / RW are the same as DVD-RAM, but it also provides Constant Angular Velocity ( also known as CAV ) for burning, where the device must maintain at a constant speed during burning processes. If it fails to do so, the burning processes must be stopped or else the disc may not be read by ROM devices, such as DVD Player or DVD-ROM. Such circumstances are called " Linking Loss ". To prevent such circumstances, DVD+R / RW has developed a " Lossless Linking " technique to provide Various Burning Rate ( VBR ).