Why are JVM memory parameters usually in multiples of 256?

Question

I have seen almost all of the JVM memory parameters usually in multiples of 256 or a round binary value - e.g. 256m, 512m, 1024m etc. I know, it may be linked to the fact that physical memory (RAM) is usually a binary number, such as 256 MB, 1 GB etc.

My question is does it really help the memory management in anyway if JVM memory is set to a value that is a multiple of 256 or any binary value for that matter? Does it hurt to keep the JVM memory a round decimal value, such as 1000m, instead of 1024m - though I have never seen any JVM using such a value that is considered round in terms of decimal.

The OS would allocate the mentioned memory to JVM when it is launched, so I guess, it is more of a question for the JVM whether it can manage a round decimal memory size (e.g. 1000 MB) efficiently or would there be any shortcomings.

EDIT: I know, we CAN use decimal values for JVM memory, but my question is SHOULD we use decimal values?

EDIT2: For opinions/guesses about JVM being equally efficient of handling every memory size, please share any relevant links that you used for coming to that conclusion. I have seen enough WAR on this topic among fellow developers, but I haven't seen much of concrete reasoning to back either - decimal or binary value.

Answer 1

It is not necessary to use a multiple of 2 for the JVM memory parameters. It is just common use for memory allocation to double the value if the old one isn't enough.

If you increase your assigned memory value in 1MB steps you will have to adjust the value several (hundred) times before the configuration matches you requirements. So it it just more comfortable to double the old value.

This relies on the fact that memory is a cheap ressource in those days.

EDIT:

As you already mentioned it is possible to assign values like 1000 MB or 381 MB. The JVM can handle every memory size that is big enough to host the permGenSpace, the stack and the heap.

Answer 2

It does not matter. There is no special treatment of rounded values.

You can specify the memory size within 1-byte accuracy - JVM itself will round the size up to the value it is comfortable with. E.g. the heap size is rounded to the 2 MB boundary. See my other answer: https://stackoverflow.com/a/24228242/3448419