[pron]

Most JVM implementations are similar in their capabilities (with the exceptions being some hard real-time JVMs). So when people say "the JVM" they either mean all of them (the well-known ones, at least), or the HotSpot or OpenJDK VMs, which are almost identical. Usually it doesn't make a difference.

There exists at least one commercial JVM (that I know of) that guarantees no GC pauses over a few milliseconds. It is based on HotSpot, so it offers HotSpot's advantages as well. Another implementation, based on IBM's J9 JVM, also guarantees no pauses but may require configuration (that one also supports hard real-time uses IIRC).