If your OS and BIOS can recognise the whole 300gigs, you do not HAVE to partition it. If your OS is telling you your new 300 gig drive is only 105, then partitioning it into 3 x 100gig would mean you can use the whole drive.
There are arguments on both sides of the partitioning fence - I always partition so I can:
- defrag my 'files' partition quicker
- back up by copying a whole drive knowing it just contains files I put there and not stuff I could reinstall from CD/DVD
- when/if all goes pear-shaped I can re-format one partition, and the other partitions [and hence data, files, etc] stay in place - quite useful if Windows corrupts, and you need to re-install the OS from scratch
- some people like keeping songs/audio on one drive, programs on another, OS on another as a form of keeping things organised
Some experts (eg the guys at PC Format) say that partitioning is a waste of time these days [as long as your system can see the big partition] because:
- it doesn't achieve anything that creating folders doesn't do
- if you run out of space on one partition (normally the one Windows is installed on as many programs INSIST on being installed into C:\program files and Windows also likes to be in C then you have some work cut out to reorganise and move the partitions to make more room
- with modern disks, defragging is rarely necessary to get the performance required to sustain multi-channel audio and video.
I think what I am saying is - as long as you can see your 300gigs, then it is up to you if you partition. If you can't see it all, then partitioning is one straightforward way of utilising all the space on the disk. There are other ways depending on the disk, the OS, the BIOS, etc.
L0W's on the beam -- partitioning at one time had desirable performance consequences (due to sectoring, mostly); and, in cases of very large drives, it was mandatory in order to access all of the drive space.
These days, though, partitioning is largely an organizational preference; but, short of truly enormous drive -- unnecessary on most current operating systems.
I do suggest occasionally doing a defrag, however, especially on drives that take heavy traffic.
The typical sort of work one does with audio editing, for insance, can tend to scatter chunks of huge files all over the platters... and eventually that takes a toll, particularly if you're running close to the edge on performance to begin with.