after partition HDD shows less GB

Hello Everyone,

Hope somebody can help me to sort this out.

After many problem to build my new Rig, (15 days) I got XP Pro Sp2 x84 and Vista Home Premium Sp1 x64 working fine in dual boot for one week.

I was not using Xp since all my Games were running fine with Vista x64, but I start to have problem with Catalyst ATI software for my Video Card and finally finish having BSoD on any load of Vista (either safe mode, last good configuration etc...), same with XP; so I decide to do a full clean re-install.
First load XP and during installation eliminated all Partitions on both HDD and re-partition again. When choosing the partition to install XP automaticly first Partition of first HDD got format as FAT16 for Boot file and the one for XP on second HDD NTFS and automaticly was showing the rest of Partition as Logical and I need 3 Primary and 1 extended.
I was worry since I read that Vista does not like FAT16 and also having no other Primary will not be able to move my Paging Files. But anyway I installed also Vista and everything was looking good but again after installing all necessary Drivers again BSoD.

So I used Secure rescue with G-parted to clean again both HDD and Partition all as I wanted 3 Primary all NTFS.

First time I install XP after final load It freazed on desktop, like it was thinking for more than 30 mn , Light from front case of HDD activity was always on but icon of mouse was moving and Keyboard was active. SO I did a Soft reset and since always get XP starting to load but freezing before the Logo screen appears, staying with Black screen.

So I re-install XP after that I had 2 entries in Boot and 2 Windows directory I eliminate the ones from first installation from Boot file and Directory in Explorer, reboot with no problem except that now I realize that my HDD are not showed the size hey should be:
My Western Digital 500gb SATA 3gb shows a total of 465.76GB (wow I lost 35GB) and it only has the Boot file on first Partition
My Maxtor 160gb SATA 3gb shows a total of 149.05GB (11GB lost???) and only with XP installed on 3d partition

WHAT HAPPENED? Somebody can explain me, please? Is that Gparted being base on Linux has messed with my HDD. Both are new and Im pretty sure that first time I install everything both HDD were showing total amount of GB they were announced for.

(On attachment my actual Partition set-up)

Thank you in advance for your answers.

The answer is that hard drives are traditionally measured by the maker such that 1GB = 1000MB, 1Mb = 1000KB, 1KB=1000B, whereas operating systems use powers of 2 such that 1GB = 1024MB, 1MB = 1024KB, 1KB = 1024B. It looks like you're getting more for your money, much as CRT television sizes quoted such as 21" were not the actual picture size, now given in small print as an inch or so less.

So 500GB = 500 x 1000 x 1000 x1000/(1024 x 1024 x 1024) = 465.67GB (or Gib, Gibibytes, if we're being pedantic).

Added to that is a small loss due to formatting reserving space for file allocation tables, etc.

Thks CPEMMA for the explanation, I though maybe these lost GB were because doing the partition through G-Parted and since the process time is very short in comparasion to Partition and formating tools in XP, so my Noob mind concluded it was partitioning but not Formating well and instead of deleting all old partition files of my previous OS installation it was using a hided space on HDDs to keep these old files.

Thks again