Here are 23 pages of extensive notes on the not-so-obvious bits of the OCR F451 syllabus (for the January 2010 exam).
As always, these notes were written for me to revise from, and so there may be bits that are not covered as much as you need to learn them in, or there may be bits that are covered in nauseating detail for you because you are already 100% familiar with them.
Original document is a Word 2007 (.docx) which if you want, email me and I will send you a copy.
These notes cover all six topics within Unit 1:
Components of a Computer System
Data: Its Representation, Structure and Management in Information Systems