Of buffers

vi keeps a number of buffers including the current one.

y	Yank to buffer
p	Pull from buffer to after cursor
P	Pull from buffer to before cursor

Any of those commands can be prefixed with "id Where the ID specifies a particular buffer. Pulling from a buffer does not empty it - you can pull multiple times to copy something.

Numbered buffers

Deletion actually copies to one of the numbered buffers. Last deleted block goes to buffer 1, one before that buffer 2 etc.

"1p	Recover the last deleted block
"1p....	Repeat the pull - special case on number buffered, goes back to previous ones

Alphabetic buffers

A series of buffers for your own use exist labelled a-z. Useful tricks include:

    "aY
    :e anotherfile
    "ap

To copy between files.

Buffers are also where good deep vi macros are built using the @buffer id command.