What is JVM and what are the types of JVM?

JVM is a Java virtual machine which computer run a Java program. As described, there are three characters of JVM viz. 1. specification 2. implementation, and 3. instance. Data types of JVM is, float, double, returnAddress and reference. Their detail as below;

float - 32-bit IEEE 754 single-precision float,
double - 64-bit IEEE 754 double-precision float,
returnAddress - address of an opcode within the same method,
reference - reference to an object on the heap, or null. They run within this code / program of Java.

Here are some of the answers to your questions.

1. Default released JVM implementation is for the Java. There are other implementations of the language. Some of the known languages under this implementation are : JRuby, JPython, Scala, Clojure, Groovy etc. There are many other languages made for some specific purpose which make use of JVM implementation.

2. JVM does the conversion from the specific language code to bytecode and also makes use of JIT compiler to run it. JIT is usually specific to the programming language tweaked to improve performance of the language.

Depending on the reason of the inception of JVM based language it's specific purpose could be different. For example, scala and clojure both target different set of problems. Whereas JRuby and Jython both are pretty much same as ruby and python respectively but just make use of JVM.

Some of the JVM implementation are specific to some machine learning and artificial intelligence problems. So each JVM implementation has it's reason for inception. And the implementations differ based on that.