alters the type of the variable and also changes the length. For example, to change numeric to string or vice versa. You can use this command for single, multiple or ALL variables in your file. Here is the command for all variables.
ALTER TYPE ALL (A=A200).
the above will convert all the numeric to string with 200 character length. But it does not allow you to create a new version of the variable (unlike RECODE OR AUTORECODE).
For a good description of converting variable type see this UCLA page:
Another good page to look at this is at the following user comment in a google group: