Why is my 8GB MicroSD card not actually 8GB?

MikeHunt79 · 19 May 2011 at 07:18

I have 2 different cards, 2 different brands (Sandisk and Transcend) and neither one seems to be 8GB:

Is there a way of repartitioning these cards so I can actually get 8,000,000,000 bytes?

Predicament · 19 May 2011 at 07:22

Hardware Knowledge said:
The difference in capacities is due to two different methods for defining what exactly the prefixes mega, giga, tera mean. In the computer world, these prefixes have different meanings depending on what exactly you are talking about. Hard drive manufacturers report the size of hard drives using the decimal definition of these terms (10^6, 10^9, 10^12 resepctively), whereas operating systems and other software use the binary definition of these terms (2^20, 2^30, 2^40).

As you can calculate, these values are close, but not exactly the same

40GB = 37GiB
80GB = 74GiB
100GB = 93GiB
120GB = 111GiB
160GB = 148GiB
200GB = 186GiB
250GB = 232GiB
300GB = 279GiB
320GB = 297GiB

You get the idea.

RJC · 19 May 2011 at 07:22

You wont, its how the Windows calculates the capacity, they use a different calculation to what manufacturers use.

paradigm · 19 May 2011 at 07:41

RJC said:
You wont, its how the Windows calculates the capacity, they use a different calculation to what manufacturers use.

You mean the OS uses the correct value of Kilo/Mega/Giga/Tera.

The OS sees multiples of 1024 bits, the manufacturers of disks about 15 years ago decided that using 1000 made their products look better than they actually were.

RJC · 19 May 2011 at 07:49

Could not remember which way round it was

PhillyDee · 19 May 2011 at 08:21

Even so, op is still
35 016 704
bytes short (of a picnic)

Duke · 19 May 2011 at 08:30

Try formatting in NTFS.

Richdog · 19 May 2011 at 08:31

You joined in 2004, and ask such a noob question like this? Jesus.

pv123 · 19 May 2011 at 09:50

Richdog said:
You joined in 2004, and ask such a noob question like this? Jesus.

You joined in 2005 and you still don't have any manner, Jesus!

Hutch-Sco · 19 May 2011 at 09:53

Its false advertising sue them lol

MikeHunt79 · 19 May 2011 at 09:53

I already know that a 8gb can equal 8,589,934,592 bytes or 8,000,000,000 bytes depends on how it's calculated, but I only have 7,964,983,296 bytes which is less than 8gb no matter how you calculate it...

PhillyDee said:
Even so, op is still
35 016 704
bytes short (of a picnic)

I see you actually looked at the amount on bytes on my screenshot...

Duke said:
Try formatting in NTFS.

Thanks, I'll give that a go.

Richdog · 19 May 2011 at 10:00

pv123 said:
You joined in 2005 and you still don't have any manner, Jesus!

Manners.

Sorry, but this is literally one of the oldest, most-asked, and easily-researched IT questions on the whole of the interweb, I was just surprised to see it from a very senior member.

HeX · 19 May 2011 at 10:03

You'll also lose space to the File Allocation Table, which is probably where your missing bytes are.

Ch3m1c4L · 19 May 2011 at 11:04

Richdog said:
Manners.

Sorry, but this is literally one of the oldest, most-asked, and easily-researched IT questions on the whole of the interweb, I was just surprised to see it from a very senior member.

yea, but if you use your eyes and look at his post, that wasnt what he was asking, he was asking why he didnt have enough bytes

MikeHunt79 · 19 May 2011 at 11:24

Richdog said:
Manners.

Sorry, but this is literally one of the oldest, most-asked, and easily-researched IT questions on the whole of the interweb, I was just surprised to see it from a very senior member.

Well I'm still looking for my answer...

I still don't know exactly why my so called 8Gb cards are not in fact 8gb, which is turning out to be a bit of a pain, as I'm trying to make a clone (including bootblock) of another 8GB Sandisk Cruzer USB memory stick, which has a partition size of 8,000,012,051 bytes to be exact.

Right now my only option seems to be to order a 16gb memory stick, which I'd rather not do as I need to get this done this weekend really...

HeX said:
You'll also lose space to the File Allocation Table, which is probably where your missing bytes are.

Ok, I found windows to be a bit of a pain as far as partitioning stuff goes, so I had to resort to using a Mac.

Anyway, using Disk Util, I managed to find out the capacity of the whole device (not just the partitions), in fact I even removed the FAT32 partitions from both of my 8Gb memory cards before doing these screenshots.

Here's the capacity in Disk Util of my 8gb Samdisk MicroSD card:

Here's the capacity in Disk Util of my 8gb Transcend MicroSD card:

And finally I managed to borrow a 16Gb Sandisk Cruzer USB stick from someone for comparison:

So we can clearly see that the 16Gb Cruzer is more than 16,000,000,000 bytes while my MicroSD cards are less than 8,000,000,000 bytes. So I guess I'm going to have to order some 16Gb cards in order to clone an 8Gb card then?

weird_dave · 19 May 2011 at 12:33

The raw capacity of the flash chips should be the `true` 8/16GB value of 8589934592/17179869184, but you never see it because the manufacturers use the space for nefarious marketing purposes. Kinsgton and Sandisk both state 8000000000/16000000000, the extra space is used to increase the life of the drive at its stated capacity as cells die. Some of the spare space is for the 'housekeeping' area which handles the bad sectors.
You can blame HD manufacturers for the K=1000 malarky, flash disk makers realised they could benefit from not giving us the real capacity and copying the HD manufacturers numbering system.
If you take a look at the specs of an actual flash chip, you can see the raw capacity:
http://www.spansion.com/Support/Datasheets/S29GL-P_00_A13_e.pdf
Then on top of that you have the filesystem overhead.