[Businessasusuall2008]

Does anyone know what the difference between the data capacity of a hard disk and the available capacity of a hard disk is?

I will be grateful for your replies

cheers

[Dave Hybrid]

Well a 160GB drive will normally give around 150GB formatted, the space is taken up with file tables and the boot partition.

It differs from drive to drive, but somewhere around 5% I guess.

[Businessasusuall2008]

thanks for your reply Dave...

...any chance you could further elaborate on your explanation as I am trying to be more computer illeterate but have some difficults understanding all the technicalities at the moment

P.s Am guessing that what you mean is that when you have a hard disk and connect/instal it, i never has its entire memory as stated i.e. 30GB would end up being 27.9GB available capcity and the 2.1GB would be the data capacity?

[alex]

whilst formatting does have an effect it's not the primary cause of the disparagy in the measures.

What does mainly cause the difference is manufacturers of storage medium's quote a megabyte as 1000kb's (kilobytes). This is a decimal format.

But your computer measures the storage in binary (the correct way) so a megabyte equals 1024kb's.

As you can see when you have a drive of a few hundred gigabyte capacity, this disparagy of 24kb per megabyte soon add's up.

[Businessasusuall2008]

cheers Alex...

So if a Western Digital Hard Diskette Has 24 heads, 240 sectors on each track, and 6500 cylinders. What would the difference be and how would i work it out?

[Mike0001]

Originally Posted by Businessasusuall2008 cheers Alex... So if a Western Digital Hard Diskette Has 24 heads, 240 sectors on each track, and 6500 cylinders. What would the difference be and how would i work it out?

At a guess,

24*240*6500*512 bytes

19 Gb?

[Businessasusuall2008]

thats the answer i got mike so i guess it must be right then thanks

So to conclude this discussion


Available Capacity is that whats left after a disk is being formatted

and Data Capacity is that which is taken up from the formating?

Is this correct or getting the wrong end of the stick?

[DreamHazard]

Available capacity is what's actually storeable(?) on the drive, and data capacity is the theoretical amount that can be stored on the drive. Formatting a drive with smaller segments would increase the amount of data you can store on the drive, but will increase fragmentation. if you have an allocation size of 1024 bytes, a file only one byte long would take up a kilobyte on the drive. Any remaindered bytes are stored in a full allocation block. So if you save a file that's 1025 bytes long, it will actually take up 2048 bytes on the physical drive.

[Mike0001]

Originally Posted by Businessasusuall2008 thats the answer i got mike so i guess it must be right then thanks So to conclude this discussion Available Capacity is that whats left after a disk is being formatted and Data Capacity is that which is taken up from the formating? Is this correct or getting the wrong end of the stick?

There are lots of ways to format a drive, FAT, Fat32, NTFS, Ext3 (Linux) and all have some overhead. There is a partition table and Fat uses blocks of pointers to link all the sectors in a user file together. But the biggest hit is in laying down sectors along each track. There are "blank" sections between them that are effectively wasted. The most efficient use in one sesse would be if each track was a sector, but then a small file would occupy a whole track, very wasteful.

I think the "quoted" capacity assumes all of each track is usable. For some applications that would almost be true, eg, video recorders. Thus 20Gb=20,000,000,000 bytes, which is rather less in real gigabytes, measured as 1,073,741,824 bytes. You then lose some through laying down 512byte sectors, so you end up with your 19Gb drive. But then, you will almost certainly not be able to use all of that as for instance Fat uses clusters of sectors at a time to store files. If 64 sectors were used per cluster, say, then on average each large file would waste 32 sectors and small files would waste even more.

But the real con is in equating 1,073,741,824 bytes with 1,000,000,000 bytes in specifications!

[DreamHazard]

Originally Posted by Mike0001 the real con is in equating 1,073,741,824 bytes with 1,000,000,000 bytes in specifications!

Which every manufacturer seems to do.