CF card capacity - different to usual

Hi,

I just got a new CF card, 1Gb. When formatted in my camera it shows up
as 980Mb. The thing is, my other 1Gb CF cards all format to 988Mb. Why
should this one be 8Mb smaller? Assuming it's a bad block or some such
thing, would it remain stable that way, or is the card likely to
deteriorate?

(Cards are all Sandisk Ultra II. Camera is Canon EOS 5D)

Thanks for any advice,

John

 

I have no definitive answer, just another data point.

I have 3 Sandisk UltraIIs, one 2GB and two 1GB. I got all three
from "reputable" dealers, so I don't THINK that any of them are
fake.

One of the 1GB cards has the serial number along the "side" edge.
The other 1GB card and the 2GB card both have the serial number
along the "bottom" edge.

The cards with the "bottom" serial indicate they will hold
111 and 222 RAW pictures from my Canon 20D. The 1G card with
the "side" number only indicates 109.

After formatting in the camera:
2G (bottom) card shows 65,536 used, 2,039,480,320 free
1G (bottom) card shows 32,768 used, 1,011,367,936 free
1G (side) card shows 32,768 used, 1,011,367,936 free

I can't figure out how to show if there are any "bad sectors"
on a CF card, and I've been using both of the 1G cards for
more than a year with no problems. But SOMETHING must be
indicating to the camera that there's less available space
on the 1G (side) card...

 

Hmmm... strange things, these CF cards.

Some more data..

My cards show (when formatted in the camera)
32,768 used 1,036,042,240 free (x4)
32,768 used 1,027,827,472 free (the one I am asking about)

So, that's slightly more confusing. Why should my 1Gb cards format to a
different size to yours?
Mine five cards vary slightly in appearance, which I put down to be
different ages and Sandisk changing their labels, but maybe some are
fakes? I hadn't really considered this for small value items like this,
but I guess they could be.
Sandisk tech. support aren't a lot of help either. Don't seem that
knowledgeable about their own product, to be honest.

I guerss, at the end of the day, 8Mb =/- on a 1Gb size card doesn't
really matter, and I got it pretty cheap, but I'd just like to know
what's going on. Also I'd like to be sure the card won't suddenly lose
some more space, with my pictures in it!
Sadly, as with a lot of IT things, getting the real facts is difficult.

John

 

And, computers in general.

There's another question for the gallery... but, I *am* using
a 20D. It's possible there was a "format change" between the
20 and the 5...

I really don't know. I've heard about people getting "ripped off"
on ebay, but I thought, in general, the tip off was the card SPEED,
not the capacity.

That confirms what anecdotal evidence I've heard, too...

As I said, even my one "weird" card has been ultimately dependable.
I can't say if it's a "bad sector" deal or what. If I was a "pro"?
I'd probably chuck it and get another. As it is, the "weird" card is
now my "spare".

Agreed. Hey, if you hear anything else, please post it here? I've
checked with my regular (non-photo) IT guy, and he can't think of
any "easy" answers. I'll be watching the thread, and hoping that
someone comes up with SOME kind of definitive answer before I leave
for the Grand Canyon in 2 weeks!

Good luck!

 

Flash cards are designed to appear as if they're hard disk drives.
That means that they should indicate a fictitious number of
cylinders, sectors per track and platters. For instance, a ten year
old WD Caviar 1.6GB hard drive has on its label:

With a sector size of 512 bytes, that works out to 1,624,670,208
"marketing" bytes. Dividing by 1024 * 1024 results in 1,549.4 MB.
Another hard drive manufacturer might have made a hard drive with
3252 cylinders, 15 heads and 64 sectors per track (and the same
sector size) and gotten a 1,601,372,160 byte drive (1,527.2 MB).
Both probably would have been marketed as 1.6 GB drives.

Many flash memory cards have more than the reported amount of
memory. Some of it is used to remap bad sectors (when they occur)
so that the drives continue to function without appearing to have
lost any capacity, at least while there are spare sectors remaining.
I don't know if any of your camera's memory cards do this, though.
It depends on how the cards were designed. Whether a given card has
a slightly smaller or greater reported capacity than one from
another manufacturer, or a different model from the same
manufacturer, it won't be a good predictor of the card's quality.

 

It can depend on what the card tells the camera.

More peculiar is that the odd one you are asking about is clearly not a
multiple of any valid blocksize for a FAT formatted disk (is there a
typo???)

1,036,042,240 = 16 x 1024 x 63235
1,027,827,472 = 16 x 64239217 (most odd)

I'd expect a cluster size of at least 1024.

Regards,
Martin Brown

 

Martin,

You're right, I had finger trouble.
Correct figure is 1,027,817,472.

ohn

 

I had another reply from Sandisk, saying that it might be a mapped-out
bad block, but they strongly suggest that it's a hidden file put there
by the OS. That can't right though as I don't see why the camera would
put more hidden files on one CF card than another apparently identical card.

I've often thought that companies have a few people who really know
what's what with their products etc. but these guys are in some kind of
'inner sanctum' and communicating with them is hard. The average help
desk guy just doesn't have the detailed knowledge to answer many of the
questions posed.

Oh well, it's only a CF card. I think I'll give a it a good test though,
before using it on something important.

John

 

I've formatted all the cards both in the camera and with windows,
and the "bytes free" numbers remain the same, but that one card
STILL holds 2 fewer pictures.

Good luck!

 

On Thu, 29 Jun 2006 16:14:06 -0400, Philip Bailey wrote:

:: from an earlier msg ::
: After formatting in the camera:
: 2G (bottom) card shows 65,536 used, 2,039,480,320 free
: 1G (bottom) card shows 32,768 used, 1,011,367,936 free
: 1G (side) card shows 32,768 used, 1,011,367,936 free
:
: I can't figure out how to show if there are any "bad sectors"
: on a CF card, and I've been using both of the 1G cards for
: more than a year with no problems. But SOMETHING must be
: indicating to the camera that there's less available space
: on the 1G (side) card...

If there were a few bad sectors that weren't remapped, the free
space would also be reduced. That apparently isn't the case. The
camera has found some other difference between the cards that you
(we) still haven't also determined.

If you don't have a disk utility that shows the types of format
and block sizes of the cards, try this. Immediately after
formatting both 1GB cards, copy a very small file (less than 1kb but
greater than zero would be ideal) to both of them. Then compare the
remaining free spaces. It's possible that the cards don't have the
same file allocation block size, and one is more efficient in
utilizing disk/card space, while the other (if it were a hard drive
and not a flash card) would have a slight speed advantage. The
number of pictures your 20D thinks it can store on the card is only
an estimate, and both cards might end up holding the same number, or
the difference could be even more pronounced than the 20D's
estimate. Since pictures vary in size, the only way to really know
if there's a real difference would be to try to copy all of the
pictures from one of the cards (when it's full) to the other card,
and if they all copy, compare the final, remaining free spaces.

 

Update...

The vendor says that the card I bought is Asian spec. which is different
from the European ones. That seems to make sense (to me, not being an
electronics expert) - presumably the actual chips inside are different,
resulting in a slightly different capacity. The 1Gb is only a nominal
capacity of course, so it would still qualify as being 1Gb.

The card seems to work fine, and I got it at a good price (eBay) so I
guess that's it - sorted.

John