Windows 7: Hard Disc writing and erasing

I have a question on what happens after writing and then erasing large files onto a HDD?
Let me explain:
I put 3 banks of sounds and instruments on a new HDD, (300GB) one after other.
3 Folders, with sub-folders, size 100GB, than 40GB, last one 80GB.

I had to erase 1st one 100GB. Does it mean that there is an "empty space" in the beginning of the HDD?
What if I start to add stuff on the HDD? where is it going to be written?
Is there a way to move the 2 remaining folders to the beginning of the disc or what happens if I put a folder of 120GB? Is the folder going to be split up?
Does it effect performance of HDD?
TIA

Windows decides itself where to put files. But it makes the file contiguous if possible. If a file is modified (so you append some stuff to end of that file), that portition can not really be appended to the end (another file is already there) and windows places it somewhere is.

Since you're only copying/deleting stuff the files will stay contiguous. But folder itself isn't contiguous in your case (folder 120GB will be split up).

It doesn't effect performance a lot. (Probably you don't even see any difference). To make everything contiguous.... defragment your drive with Windows 7 disk defragment

The article at the following link provides a good explanation:

Disk Defragmentation Explained

HTH

With today's fast hard drives a file must be very badly fragmented before you even notice any lag.
Everything written on a HDD is split in blocks and in the header of a block, the drive finds the address of the next block so it can read your files completely and in order even if those blocks are not contiguous but spread all over the place. (which is more often than not the case since every drive in use becomes fragmented over time)

As Kaktussoft already said: if you concerned run the defrag process:
Either go to Computer and right click the drive in question, go to properties and there use the Tools Tab
Or put defrag in the search dialogue of your start menu.
Via control panel you can even set up a scheduled defragmentation that can take place while the computer is not in use
(Mine runs every Wednesday at 1 am)
-DG

Thank you all for the clarification and the link.

I defragment manually once a week, I don't want to do the scheduled one, because I am afraid that it will defragment my SSD-HD, which I don't want done.
I know there is a choice, which HDs to do, (I have it done on my other PC like that), but I don't trust it.

Again, many thanks for taking your time to answer.

All the best in 2013.