A query should not be dependent upon an operating system. Oracle's multi-protocol facility manages this aspect of distribution.
A distributed database is a database that is under the control of a central database management system (DBMS) in which storage devices are not all attached to a common CPU. It may be stored in multiple computers located in the same physical location, or may be dispersed over a network of interconnected computers.
The RDBMS should be able to run under any operating system or at least under any of the popular operating systems. Do not allow your choice of RDBMS to tie you to a particular operating system.
Oracle is certified on at least as many operating systems as hardware platforms. However, be warned that the more popular operating systems monopolize the attention of most of Oracle's development and support staff. So, if you are running on HP-UX, Sun Solaris, or Windows NT, you will not have any problems acquiring the latest versions of Oracle's RDBMS. However, those of you on operating systems that are less popular and/or nearing extinction, such as VM or VMS, will have to wait.
A distributed database is a database in which storage devices are not all attached to a common CPU. It may be stored in multiple computers located in the same physical location, or may be dispersed over a network of interconnected computers.
Collections of data can be distributed across multiple physical locations. A distributed database can reside on network servers on the Internet, on corporate intranets or extranets, or on other company networks. The replication and distribution of databases improves database performance at end-user worksites.