There exists a website which in fact had an earlier memory limit of 12 Megabytes (12 Megabytes in php.ini, and 16 Megabytes in configurations.php) and labored formerly.

After moving to a different server it began giving memory limit errors and exhibiting half-blank screen.

We increaded the limit both in files (php.ini and configurations.php) and today it really works, however i dont know how is it feasible that now it requires a substantially bigger quantity of memory (previously use 12 Megabytes, now it cont use under 20 Megabytes).

I suppose you didn't alter the OS along the way. Moving from Home windows to Linux or the other way around is very prone to change resource usage.

Which is a lengthy shot, but possibly you moved from the 32-bit system to some 64-bit one? This could slightly increase memory usage as addresses (pointers) are two times as large on 64-bit architectures, and code with a lot of small objects uses lots of pointers.

Overall though, we can not let you know much without seeing what transformed concerning the system.

12 is not high enough, if you do not only use drupal because it is. Greater is recommend, than more modules you'll install, usually 96MB is sufficient with image processing...

12 Megabytes is actually really low. I'd tend to disregard it and continue.

Ideas what might have transformed, though:

  • That old server might have had modules installed that reduced memory usage, e.g. memcache

  • The brand new server might have to depend on GD library for image processing, as the old server maybe had ImageMagick (that is an exterior oral appliance does not count for the memory limit)