Thanks for stopping by my blog and adding value to one of the blog articles. The explanation in your book is very good – I must admit that I have not had a chance to read up to that page during the second read through of your book, otherwise your formula probably would have been mentioned in this article.

Your book’s formula seems to produce a number that is close (typically +/- 5) to the reported DB_FILE_MULTIBLOCK_READ_COUNT on Oracle 11g R2 when using the reported “Database Buffers” value that displays when the database instance starts. I did not check the __DB_CACHE_SIZE hidden parameter, so the actual memory for the buffer cache may have been slightly different due to the use of the SGA_TARGET parameter.

I shared my opinion about 1 at the bottom of page 178 in TOP…
http://books.google.com/books?id=b3DIkYO2gBQC&pg=PA178#v=onepage&q&f=false

Cheers,
Chris