Calculating HDD Partition Sizes

  Danoh 10:45 06 Nov 2004

A new PC with a 160Gb HDD formatted as a single drive shows only 149 Gb available, losing 11 Gb somewhere.

In reformating a new 160 GB HDD (NTFS, 4Kb) with multiple partitions, I've tried to calculate the optimum partition sizes to land on a cylinder boundary but am not sure I've got it right as the end result is still 11 Gb missing.

The BIOS is set to Auto detect and comes up with;
160,041 Mb available, which with the default 1024 cylinders set up, should equate to multiples of 159 Mb to be used to fall on cylinder boundaries.

Is this correct?

Running Windows XP SP2, 1st primary & active partition followed by an extended partition with 3 logical drives (for now).

  Peter 11:02 06 Nov 2004


Unlike memory, hard disk manufacturer calculate their hard drive capacity using 1,000 = 1K, 1,000,000 = 1M, 1,000,000,000 = 1G. It makes them look bigger than they are!

When Windows looks at the capacity it use 1,024 = 1K, 1,048,576 = 1M, 1,073,741,824 = 1G. Therefore your 160 G needs to be divided by 1.073741824 to give its true capacity of 149.0116119385 which accounts for your "lost" 11 G.


  [email protected] 11:04 06 Nov 2004

suggest you set primary 1st partition @ 20G then divide the rest into the number of partitions you want. Xp + office normally takes up to & sometimes over 11G including your progs
Reason is primary HDD partition on which your OS is normally speedier if on start up it only has to search thro 20G as compared to anything bigger

  Danoh 11:41 06 Nov 2004

Wow guys!! That was fast!! Thanks!!

The Award BIOS shows the HDD capacity at 160,041 however.

  Danoh 17:01 06 Nov 2004

~ bump ~ to 1st page; any further suggestions please? Thanks.

  bremner 17:17 06 Nov 2004

Peter has explained why your drive shows 149GB.

Logical Block Addressing has replaced Cylinders / Heads and Sectors as the way drive sizes are calculated.

The old method of multiplying the three together and then by 512 simply does not give you the drive size.

So I do not think you can actually work out where the cylinders end.

  Danoh 18:56 06 Nov 2004

Thanks all! Can't help wondering how LBA works under the covers, but time for fireworks, etc., now! Will tick as resolved.

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