Guyz, I'm not sure what u r all on about, but u do have the wrong idea about multi-session discs.
Basically, true "fixation" or "closing a disc" means just that, i.e. no more writing is possible.
For you newbies..
1. A cdrom/dvd drive will only start reading from the first TOC written in the leadin area, i.e. it will not go looking for other TOCs without this.
2. A multi-session disc works this way, after first TOC is read, it actually contains a link (multi-session link) to the location of the next TOC. So the drive uses this to read in the next TOC, otherwise, without it it will not go and read one.
3. After reading this 2nd TOC, it may also contain a link to the next 3rd TOC. But, if it was closed, then the link would have been written with address of FF:FF:FF, or there simply won't be a link entry in this TOC. So end of reading multi-session TOCs.
As u can see, multi-sessions on a CD are created by linking the previous TOC with the next new one and so on forming a chain. When a new TOC is generated in memory, it is made to link to the next empty space on the CD.
Closing a disc means that the last TOC will not link to the next empty space, so stopping the chain, and it will be impossible to create further sessions. Also, because this last TOC is already written, unless you are using a rewritable disc or u are able to rewrite to the CD-R, it is impossible to extend the disc with further sessions.
Also, the rewriter drive will not even let u write to the CD-R, unless it is a blank, or the last TOC links to a valid empty space.
Confusion & misnomers...
Lastly, "closing a session" can also have a different meaning in certain applications. In most, it simply just means writing the session project to disc with session leadout and a link to the next empty space. This is so that cdrom/dvd drives can read it. Which, this is a normal multi-session procedure. The disc is in fact a normal multi-session extendable disc.
Providing the "disc is not closed" (different from "closed session" above), any multi-session capable software will be able to write further sessions, e.g. Nero.
"Closed session" was made to distinguish between "Open session" - where, PMA (special area) was used to store the TOC/s which weren't actually written in the correct places yet. Only rewriter can read such discs.