first its called Dal
So, the DarlikVM was specificly designed for Android and for the needs of running in an embedded environment, like: limited battery, limited memory, limited cpu,...
The DalvikVM runs *.dex-Files
what are of course still ByteCodes, but which are converted at build-time from *.class or *.jar -files. After that conversion the ByteCode is highly optimized to run on Embedded Devices and so is much more memory and cpu-efficient.
It is also designed to allow multiple VM instances to run at once, relying on the underlying operating system for process isolation, memory management and threading support. Dalvik is often referred to as a Java Virtual Machine, but this is not strictly accurate, as the bytecode on which it operates is not
I assume this was enough information, wasn't it ?
If not i'll tell you some more