A database management system is a set of programs that allow users to create and maintain a database. Although there are many advantages to using database management systems, there are some disadvantages. These disadvantages include the complexity, size, performance, and associated costs of a database management system. The advantages of a database management system outweigh the disadvantages, but one must understand the disadvantages to ensure you have a complete understanding of the system. First, database management systems can be very complex and difficult to understand. Designers and end users must have the necessary skills to be able to use it correctly. Database designers must have knowledge of SQL coding to write database software correctly. Not only do they need to know SQL coding, but they will also need to learn the modified version of SQL that the database management software might use. The end user will need to understand how to run queries, generate reports, and update the database if their security level allows. In addition to the complexity of the software, the hardware required can be complex. Most modern database management systems require a central computer to host database management. Depending on the size of the database, a large mainframe and terminal system can cost hundreds of thousands or millions of dollars. The mainframe computer required could have extreme processing power and allocated memory compared to most personal computers. This makes the mainframe an expensive piece of equipment and a significant investment for most businesses. Maintaining the mainframe and database system could be costly in itself. Mainframe maintenance involves replacing defective or near-defective parts, which will ensure the database is available for as long as possible.