Up to version 10, the regular window version has a maximum of 215 – 1 = 32 767 variables and a maximum of 231 – 1= 2.15 billion cases.
The student version is limited to 50 variables and 1,500 cases.
Starting with version 10, the limit on the number of variables has been removed, the only "hard coded" limit is 2.15 billion variables. This does not mean that it would make sense to work with millions of variables. It is always more efficient to load only the variables you currently need.