Virtual arrays are arrays that are  stored  on  a  mass  storage  device
  rather than in main memory.  You use them just as you use normal arrays,
  but you must specify a different form  of  the  DIMENSION  statement  to
  allocate  them.   You  should  explicitly  initialize  all  variables in
  virtual arrays at the start of your program.

  Virtual arrays are supported to provide  compatibility  with  BASIC-PLUS
  and  BASIC-PLUS-2  and are not recommended for use in development of new
  BASIC programs.