What is process.memory giving ?

Yes, memory units of 20 bytes is right. Just for anyone else:

1988 (after reset) - 1841 = 147
147 * 20 = 2940 bytes

Note: I've discovered a bug here, which is that process.memory().history (which is the amount of memory used for the command history) is being calculated wrong, and so that knocks all the calculation of 'free' memory out. My info below is with a development version that now has this fixed. When 1v48 comes out that should have the fix in.

What I think is happening is that the script is being executed, and is generating variables/functions which are using up more space than just the individual characters. If you just had one function that wasn't executed then the situation would be a lot better.

For instance:

>process.memory() 
={"free":1988,"usage":12, ...

function foo() {
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXX
}

>process.memory()
={"free":1953,"usage":47, ...

So the code above (which, incidentally is 490 characters) uses 35 blocks in total which is 700 bytes.

Of that:

You can type trace() (a debug tool for developers) which outputs the raw structure of the interpreter's data, and that might help to explain where your memory is going...