When you link or open external tables in a Microsoft Jet database, it’s easy to forget that you’re accessing the data through an additional service layer (the IISAM or ODBC driver). When you consider the amount of overhead involved in maintaining a connection, transferring and translating data, and maintaining a remote index in a foreign format, you can see why certain Microsoft Jet operations are significantly slower when executed against an external data source. The first part of this section discusses one way to dramatically increase performance when you only need to read data in a single pass. The remainder of the chapter focuses on two common problems: connections and temporary space.