>1 Virtual Shared Memory Segment slow down

I've been told by Informix that having >1 virtual shared memory segment slows down your Informix Online Database server. Informix normally has 3 share memory segments 1 Fixed size 'Resident' shared memory segment for disk cache etc. 1 Fixed size 'Message' shared memory segment for communication with clients. and 1 Fixed size 'Virtual' shared memory segment Addition 'Virutal' shared memory segments can be added if needed. These are usually smaller than the initial one. Why would added more shared memory segments slow down the server (they are mapped contiguously but the way)?? Anything internal to any UNIX kernel which may affect performance? -- David Williams