Storage size reduces after format

Posted on 2004-10-07
Last Modified: 2013-11-15
Hi Guys,
I have an interesting query!
U have a hard drive n then u format it as n when required.Why does the total capacity of that HD always dwindle down a few 100Mb ? CD RW blanked also has the same end result...I have a 40gig here..After a few formats over time,its like total = 38gigs.

Whered my 2 gigs go.It doesnt happen to a video tape(VHS) or the defunct audio tape. Does it :))))
Question by:rajivmhas
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Expert Comment

ID: 12250897
As far as a hard drive goes, it's because hard drive manufacuters define a kilobye as 1,000kb whereas Windows defines it as 1,024kb. When you convert this to gigabytes, the size the manufacuter says you are getting and the OS are different.

As far as a CD-RW goes, a certain amount of data is reserved for things other than data, like the lead-in and lead-out tracks for instance.

and no, this is not a problem with VHS tapes or Audio cassette tapes :)
LVL 20

Expert Comment

ID: 12250944
For reference,

1 megabyte is (2^20) = 1,048,576 bytes
1 gigabyte is (2^30) = 1,073,741,824 bytes
In your case..
40GB (According to the manufacturer) = 40,000,000,000 bytes
40GB (According to Windows) = 42,949,672,960 bytes
a difference of 2,949,672,960 bytes, or roughly 2-3GB

Accepted Solution

chumplet earned 125 total points
ID: 12250950
There are a few things going on here.  

First of all, understand that a 40gig drive does NOT necessarily mean exactly 40gigs -- it's a rounded number.  Motorcycles do a similar thing.  A 850cc motorcycle may actually be 842cc, or something like that.  No harddrive manufacturer wants to sell a 39.2gig harddrive -- especially when their competitor is selling a 39.4gig model!  Drive sizes are rounded up, typically, and so your 40gig drive is likely a bit less.

Secondly, a *gigabyte* is actually 1,024 megabytes.  My harddisk at work is technically 41 billion 'bytes', but it comes out to 38.2gigs.  Regardless of all of that it is STILL sold as a 40gig drive, though the actual capacity is a bit less.  Wacky.

Lastly, if you're losing drive space whenever you format, then you're most likely getting bad clusters.  In other words, parts of your drive media are going bad, you format it, the system notes those bad clusters and marks them as defective, and they are no longer part of the available media space.  Your system does not want to write to bad clusters because data could be lost.  If this is the case (losing drive capacity with each format), then you're most likely getting bad clusters.  Not much you can do, really, but you could try a disk repair utility.

My $.02 on this.  Hope it helps!

LVL 55

Expert Comment

ID: 12251870
Even if all the clusters are good you have to lose space during the format, just like the page number in books takes up space on the page so does the format information that is written on the disl to tell the OS where it is.

Video and tape don't allow random access to data, they are sequential devices; therefore there is no format information to take up any space.
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Expert Comment

ID: 12255677
yep, the best way to describe this is the index of a book
even though the book has technically 200 pages, the index takes 5 pages or so in itself, just like the file allocation tables
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Expert Comment

ID: 12256277
When you format a drive with NTFS you create what is called a Master File Table (MFT).
This table is the "Index" or "Table of Contents" if you will, for the drive.
The size of the table depends on the size of your disk.
The bigger the disk the more entries will be required in the table and hence, the more space you will "loose" creating it.

Also it is good to bear in mind, as some have posted here already, that the HDD manufacturers use a different accounting method for what size a Gigabyte actually is thus rendering your 40GB drive a 38GB drive before you even start.

Another thing to remember is that cluster size also plays a part in the calculation of available space on a drive.
When you format a disk you do so into clusters.
These clusters are all the same size (between 1024 and 4096 bytes) and if, after dividing the disk into clusters, there is any space left over (ie space that is smaller in size than your cluster size) it is rendered unuseable.

Hope this helps you out.

Expert Comment

ID: 12256286
Oh yes, and this does not apply to VHS or Betamax or Audio tapes or Vinyl.
LVL 10

Expert Comment

ID: 12256559
this is (obviously) because hard drives don't always write sequentially but vhs and beta are recorded and read sequentially

Expert Comment

ID: 12256573
You know it.

Expert Comment

ID: 12256640
everyones correct as far as the manufacturers rounding goes, but the random access actually has nothing to do with it. along with the rounding that happens something else happens with the clusters. picture a table with empty bowls on it. lets say each bowl can hold up to one gallon of water. you have 2.5 gallons of water to pour into the bowls so you fill up two and the half of another one. along comes your friend with a half gallon of water, but once a bowl has water in it it is sealed and can no longer hold anything else. he must put that .5 gallon into another bowl. this happens with your hard drive when its seperated into clusters, when those 4kb clusters are filled with data from a program  not every clusters get filled with a full 4kb but once it has something in it information from another data source cant be put into it. its called hard drive slack.

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