This parameter allows you to specify the size of a volume to be created.
By default, NNN is a decimal number of Kilobytes. Including MB or GB after the number changes the value to Megabytes or Gigabytes.
The maximum supported volume size is 4 Gigabytes (4,000MB) on Win9x/Me, or 2048GB on NT/2000/XP/Vista/Win7, or the size of your hard disk, whichever is smaller.
SDWEXPAN.EXE also has a /Size option, but the meaning is slightly different. When resizing volumes, the /Size parameter is used to specify the new size of the volume in megabytes.
/SIZE = NNN [MB | GB]
/Size=100 - 100 Kilobytes
/Size=100MB - 100 Megabytes
/Si=1000MB - 1 Gigabyte
/Si=20GB - 20 Gigabytes