Why is the effective hard drive size lower than the actual size?

I just got a new Lenovo Laptop which has been installed with Windows 7 and is supposed to have 250 GB hard disk.

Windows 7 reports that the hard disk drive has two parts: 221 GB C: and 9.76 GB Lenovo Recovery. The sum of the two parts is 230.76 GB.

If I remember correctly, if divide 250 GB by 1024 three times, I will get 232.8 GB, which should be what the OS reports as the hard drive size. But why the sum 230.76 GB of the two parts of hard drive is still smaller than 232.8 GB?

Because NTFS by design uses a piece of your volume for a MFT (Master File Table) which holds file names, creation dates, access permissions, and contents as metadata. The bigger the volume, the bigger the chunk NTFS will need.

Actually. This is because harddrive manufacturers conform to the 1MB = 1,000 KB rule and your OS uses the 1MB = 1,024 KB rule.

This would probably account for most of your lost space. Its normal. You will NEVER buy a drive that is the size it specifies, ever. I looked in to it myself not too long ago :)

Unfortunately, life's hard and this is one of those things that annoys people non stop.

At least you are smart and understand that there is a conversion that needs to be made.

The "extra" space is usually used up by the allocation table, meta data and various other items that just make it work without you needing to think of it... it is nothing to worry about.

If you want to make 100% sure you have the correct drive, go in to device manager and expand hard drives, find the model number and Google it. If it reports the correct drive (which it should) there shouldn't be anything to worry about.

A chunk of your loss at least is due to the partition table eating it's entire track--a horribly inefficient legacy we are left with.

It could just be the manufacturer rounding the hard drive size to the nearest whole gigabyte. If we start with what Windows shows and calculate what that work out to in billion bytes:

232.8 * 2^30 / 10^9 = 249.9671 million bytes

So they just rounded the marketing size to 250, cause whose going to miss 0.0329 million bytes.

If you can get the module number of the hard drive and get it's detailed specs and find it's sector count you can determine what the actual capacity of the drive really is.