Varchar is the short form for the variable character field. This character represents data of indeterminate length. In an actual sense, varchar refers to a data column type that can be found in DBMS (Database Management Systems). Varchar columns can vary in field size, depending on whatever database is in consideration.
The maximum limit of the field in Oracle 9i is 4000 characters. The data limit for MySQL for a row is 65,535, and the field limit of Microsoft SQL server 2005 is 8000. On the other hand, Nvarchar refers to a column that can store relatively any length of Unicode data. The Nvarchar, however, must adhere to a code-page of 8-bit coding.
While 8000 is the maximum size for varchar, 4000 is the maximum size for Nvarchar. This simply implies that 8000 can be the maximum amount for a single column of varchar, while 4000 characters can be the amount of a single column of Nvarchar at the maximum.