Is 2GB really 2GB?

[Will Sawtelle]

I just bought a new 2GB SanDisk Extreme III CF card. When I formatted the card, it showed 258 remaining shots (Jpeg SHQ). My old Belkin UDMA 2GB card shows 256 shots after a format, while the 2GB Olympus Type-M XD card shows 264 shots.

While I recognize that the camera is showing an estimate of the available exposures remaining, Why are the 3 figures different?

[er1kksen]

Perhaps in order to format the card, the camera has to write a certain menu system or something to provide compatibilty, which may vary from card to card? This would take up a little space on the card and would affect the available space. I imagine this might be the least with the Olympus card because it would be already optimised to use with an olympus camera and require the least formatting.

^^^this is just a wild guess, I have little actual knowledge on this subject.

[bhrm]

I just bought a new 2GB SanDisk Extreme III CF card. When I formatted the card, it showed 258 remaining shots (Jpeg SHQ). My old Belkin UDMA 2GB card shows 256 shots after a format, while the 2GB Olympus Type-M XD card shows 264 shots.

While I recognize that the camera is showing an estimate of the available exposures remaining, Why are the 3 figures different?

also the fact that with JPEG compression, the camera only gives an estimate of shots. Its just the nature of how 1's and 0's work

Doesn't matter what brand, or what type card. Even hard drives and any kind of storage is the same story.

[Michael Meissner]

I just bought a new 2GB SanDisk Extreme III CF card. When I formatted the card, it showed 258 remaining shots (Jpeg SHQ). My old Belkin UDMA 2GB card shows 256 shots after a format, while the 2GB Olympus Type-M XD card shows 264 shots.

While I recognize that the camera is showing an estimate of the available exposures remaining, Why are the 3 figures different?

Different manufacturers interpret gigabytes differently. Originally, gigiabytes, megabytes, kilobytes, etc. were powers of 2, i.e a gigabyte is 2**30 (1,073,741,824 bytes), a megabyte is 2**20 (1,048,576 bytes), and a kilobyte is 2**10 (1,024 bytes). However, disk makers decided to measure things in terms of powers of 10, so a disk gigabyte was 1,000,000,000 bytes, a megabyte was 1,000,000 bytes. Note that a filesystem never gives you all of the bytes, since some are used for the format of the filesystem. Some flash memory makers use the power of 2 rule and some use the power of 10 rule. There have been at least two lawsuits about this.

Here is what Wikipedia has to say:
http://en.wikipedia.org/wiki/Gigabyte

[Jonathan McGee]

You don't even need to get into squabbles over the definition of GB versus GiB just to learn why two different 2GB give different sizes. All it truely means is that it's closer to 2.0GB (however they choose to define it) than it is to 1.9GB or 2.1GB. What is really required by the hardware, in the end, is that it is an integer multiple of 512 bytes (one sector). I could build a 3.145GB drive and I guarantee the vast majority of hardware would support its full capacity without even realizing how silly a number it is.

Most of these CF cards, if you break them open, will have a 16Gbit flash chip in them (maybe 2 8Gbit flashes). Things like wear leveling (which prevent the flash card from dieing on the 100th write) and "spare" sectors (sectors set aside to replace flash segments that go bad during the card's operation) all take up space on the flash and differ by make and model. Since a majority of flash chips of that capacity ship with at least one segment bad, some manufacturers may even choose to adjust the user-visible space depending on the specific chip's initial condition.

I would just make sure to buy brand name flash (Lexar, Sandisk, etc.) and not worry if it is 346 or 344 pictures. If those last two pictures mattered, you are better off buying a second card.

[Will Sawtelle]

Oh, I agree. In fact that is why I bought the second CF card. Still, I thought it a bit curious that the three cards while sold as the same capacity report different estimates of the available number of exposures.

I considered a 4GB Sandisk Extreme III, but decided on the 2GB because of the price. Maybe in a few months I'll get the 4.

[Joop]

Besides already said things, up to 2Gb you have the option to format it as a large floppy or as a hard drive. The option of a hard drive is fat32 and that will give some other results than fat16 as a large floppy. The option as large floppy is usefull when you want to use it on different operating systems and card equipment.

[cappalucci]

Also I feel that the camera makes an estimate of how many pics can fit based on latest shooting conditions I have started with a card at 256 and filled it to over 270, the camera only gives you an estimate. without changing file format