What is instruction set encoding?

Question

When designing a process Virtual Machine , the initial consideration that you make is the instruction set encoding.

Could someone please explain what this exactly means without going too much into compiler construction or computer architecture.I would appreciate it if the explanation would only touch on what to expect when designing an instruction set for a register based Virtual Machine and the importance of considering the encoding of the instruction set before design.

Some code examples would really be appreciated :)

Answer 1

I found out exactly what I was looking for by reading the following.

1. A Short Introduction to the x86 Instruction Set Encoding
2. Encoding Real x86 Instructions

I hope this helps someone :)