Overview of real-time embedded systems for non-embedded developers

As others have noted, the term 'embedded systems' covers a really wide
range of activities, which may or may not have a processor (in that
wider sense, an embedded system has embedded functionality of some
description, which may have been achieved in pure hardware).

If you are speaking of embedded controllers, then embedded.com has some
good articles (although there's a lot of ads).

Cheers

PeteS