Lenovo 278182U - IdeaPad Y430 Dual Core T3400 2.16 GHz, User Manual, Page: 6 / 150

If a portion of the hard disk space has been used for some specific purpose,
then the capacity indicated by the operating system will be even less than
X × 0.931 G.
II. A portion of the hard disk space is used for specific purposes
Lenovo computers come with preinstalled OneKey Rescue System, so the
hard disk has a special portion partitioned before delivery, which is used to
store hard disk mirror and OneKey Rescue System program files. The size
of the reserved space for this partition varies according to the model,
operating system and software of the computer. For the sake of safety, this
partition is not evident, which is commonly referred to as a “hidden
partition”.
In addition, after the hard disk is partitioned or formatted, the system will
assign a certain amount of hard disk space for the system files.
For the above reasons, the available hard disk space indicated by the
operating system is always less than the computer’s nominal hard disk
capacity.