basically, RSTP is an enhancement to STP, the main difference being the improved convergence when recalculating the spanning tree. RSTP convergers in roughly 1 second, whereas STP can take up to 50 seconds. Watch out though: not all switches support RSTP, and for some, you need the enhanced image to support it (e.g. the 2950 switches).
Have a look at this document as well:
Understanding Rapid Spanning Tree Protocol (802.1w)
The nice thing between RSTP and STP is they are compatible... so if you have a switch A running RSTP connected to Switch B running STP, Swtich A will notice that Switch B is not a RSTP switch and it will go through the 50 seconds convergence time with switch B.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...