The ff package provides data structures that are stored on disk but
behave (almost) as if they were in RAM by transparently mapping only a
section (pagesize) in main memory - the effective virtual memory
consumption per ff object.

ff supports R's standard atomic data types 'double', 'logical', 'raw'
and 'integer' and non-standard atomic types boolean (1 bit),
quad (2 bit unsigned), nibble (4 bit unsigned), byte (1 byte signed
with NAs), ubyte (1 byte unsigned), short (2 byte signed with NAs),
ushort (2 byte unsigned), single (4 byte float with NAs).

For example 'quad' allows efficient storage of genomic data as
an 'A','T','G','C' factor. The unsigned types support 'circular'
arithmetic.