JRockit JVM versus HotSpot JVM

JRockit was originally developed by Appeal and BEA Systems before being acquired by Oracle to run server software.¹ It was meant to be optimized for large applications requiring long running tasks, a lot of memory and a scalable environment, pushing optimizations for these scenarios even further than the Sun HotSpot JVM in server-mode (see also: Real differences between "java -server" and "java -client"?).

Since the acquisition of Sun Microsystems by Oracle, Oracle has communicated on a concrete plan and roadmap to have JRockit and the HotSpot JVM to converge to be a "best of both worlds" implementation, mostly built on HotSpot but integrating the most popular features of JRockit.

In fact, and as mentioned on the same blog, JRockit won't be released as a Java 7 JVM; and some of JRockit's features are being incrementally brought into HotSpot (internally even sometimes now referred to as "HotRockit").

For more details, read:

• Differences Between BEA JRockit SDK and Sun HotSpot SDK
• Differences between JVM implementations

^{1 As partially pulled from Wikipedia on March 3, 2012 at 1.50PM EST.}

There is no JRockit release for java 7. The downloaded JDK for Java 7 and Java 8 is Java HotSpot. I can confirm this for Java 7 and Java 8 jdk downloads for oracle. Link for Java 7

Here is version confirmation for java -version for JDK 1.7
Java (TM) SE Runtime Environment (build 1.7.0_80-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.80-b11, mixed mode)

JRockit and HotSpot have been merged and JDK 7 contains the first release of this converged JVM (refer Henrik blog on Java 7)

JRockit used to be regarded as better performing although I am not sure that was ever proved consistently. Oracle are currently merging JRockit and HotSpot.