The order of the rows in the absence of `ORDER BY` clause may be:

 - different between any two storage engines;
 - if you use the same storage engine, it might be different between any two versions of the same storage engine; [Example here][1], scroll down to "Ordering of Rows".
 - if the storage engine version is the same, but MySQL version is different, it might be different because of the query optimizer changes between those versions;
 - if everything is the same, it could be different due to the moon phase and that is OK.


  [1]: http://www.percona.com/docs/wiki/percona-server:features:improved_memory_engine