Instructions are basically numbers. The width of those numbers (e.g. 8-bit, 16-bit, etc) depend on the architecture. ARM instructions can be 16-bit, 32-bits wide or 64-bit wide, depending on which ...

For example, many high-level languages do not allow the programmer to specify items such as the screen's refresh rate. However, it is usually possible to specify this using machine code.

The JVM manages code compilation and optimization, so you don’t have to worry about machine instructions and the optimal way of writing application code for an underlying platform architecture.

The machine code is saved and stored separately to the high-level code. Compilation is slow, but machine code can be executed quickly. Java and C++ are examples of compiled programming languages.