When a word modifies the buffer, it sets the buffer as dirty
by calling BLK!!. BLK@ checks, before it reads its buffer,
whether the current buffer is dirty and implicitly calls BLK!
when it is.

The index of the block currently in memory is kept in BLK>.

Many blocks contain code. That code can be interpreted through
LOAD. Programs stored in blocks frequently have "loader blocks"
that take care of loading all blocks relevant to the program.

Blocks spanning multipls disks are tricky. If your media isn't
large enough to hold all Collapse OS blocks in one unit, you'll
have to make it span multiple disks. Block reference in
informational texts aren't a problem: When you swap your disk,
you mentally adjust the block number you fetch.         (cont.)
