How to make a file of the size you choose?

Hey, I have thought several times How do I make a file with size 15 GB or more. Being a technical person, the solution to the problem was either it should be a massive program or a BRRip movie. What if I want to make a file and when I make that file it lets me choose it's size. Now that idea was awesome. I read a lot and finally came to following method:

• Choose the file size you want.
• Start Windows Calculator. Now, it should look like this

Now click on View and choose Scientific (in Windows XP) and Programmer (in Windows 7/Vista).

Type in your number and then select Hex (it's on the left side along with Dec, Oct and Bin)

• Check if your converted number has 8 digits (like F457 has 4 digits) then pad with zeroes on the left (Then my number becomes 0000F457).
• Start command prompt.

          For Windows XP, click Start and then click Run. Type cmd and press Enter.
          For Windows Vista and 7, Click Start and then in Start Search Box type cmd and press Enter.

• Enter the command debug filename.dat and press Enter. Ignore the file not found message.
• Type RCX and press Enter.
• Enter the last four hexadecimal digits and press Enter.
• Type RBX and press Enter.
• Enter the first four digits of the hex number and press Enter.
• Enter W and press Enter.
• Enter Q and press Enter.

There you have it, a file with the size you told the computer to be. And as for what the file contains or is made up of. The answer is pretty simple: JUNK .

Update: The file size in step 1 has to be in bytes.