Another way to think about it is to be aware of and keep in mind all the various limitations of your implementation. If you have a program that reads some stuf

Another way to think about it is to be aware of and keep in mind all the various limitations of your implementation. If you have a program that reads some stuff into memory, then transforms it, and then spits it back out (which is basically every program)... how can it still work if the data set is bigger than the amount of memory? What if it's bigger than the address space? (figure out how to split the data up and work on segments then combine the results) Using ints or longs or whatever as an identifier? What if we have more things to identify than UINT_MAX or ULONG MAX? What if we need to allocate identifiers so quickly, and in so many different places, that contention for the next available number becomes a bottleneck? (use uuids or random identifiers) A lot of people write software with the assumption that there is an unlimited amount of memory, CPU, etc., and usually that works fine, until it doesn't and it blows up. Scalability is about being aware of all the finite limitations, and having strategies for dealing with them instead of just hoping you don't get close to them.