disk pages, buffers and blocks

Hi,
we'd like to know how disk pages map to disk blocks.
In particular, looking at the code it seems that one
page can be built on several disk blocks while in the
first lines of bufpage.h it is said that "a postgres
disk page is an abstraction layered on top of *a*
postgres disk block".
As a matter of fact, it looks quite reasonable to have
more than a block per page.
We've also found out that a postgres buffer contains
exactly one disk block, but we'd like to understand
how pages, blocks and buffers relate to each other.

Thank you very much for your help!
regards, alice and lorena

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