Real size of a 1 gig SD Card

[pivaska]

I just purchased a Lexar 1 gig SD (32X) and popped it into my Tosh E800. When I read the free space it says that it has 975.6 free. Does anyone know what they are doing with about 25 megs of space or is it really a 975.6 card and not a 1 gig card?

[Darius Wey]

The 1GB specified is only ever present in a raw, unformatted format. This applies to all memory based cards...even your hard disks! Ever wonder why you buy a 120GB HDD only to find it has a few GB less? It all goes into the formatting information used to make your card readable.

Hope that helps. :)

[applejosh]

In regards to the hard drives (I haven't looked around enough to see if this applies to flash memory cards), not only will you lose some space in the formatting, but the manufacturers look at bytes and then convert them using base10. So, according to the advertising execs at the hard drive companies, 1000 bytes = 1 kb, while a computer doesn't use that conversion ratio. It sees 1024 bytes = 1 kb since it calculates things on base2 (or binary) numbers. (1024 = 2^10 or something like that)

[pivaska]

So what is being formatted if there are no disks involved and how is it formatted as opposed to a disk?

[CiscoKid]

The Windows Mobile Operating System still needs to format it so that it can use the memory space - exactly like a hard drive.

[Wiggster]

To elaborate on the previous points:

A gigabyte is 2^30 bytes (2^10 (1024) bytes per kilobyte, 2^10 kilobytes per megabyte, and 1024 megabytes per gigabyte.... 2^10 * 2^10 * 2^10 = 2^30, or 1073741824 bytes). Almost every storage medium is measured in the "rounded" version of "1 MB = 1000 KB", based on base 10. So, a billion bytes (1000000000) is sometimes referred to as a Gigabyte in selling storage. But actually, a billion bytes is 953.67 Megabytes. So in the conversion from the easy-to-calculate-base-ten and the actual-base-two, you lose about 4.6% of the space you thought you'd have. But I don't think that the SD cards being sold as 1GB are really 1 Billion Bytes.

Also, space is always lost when a file system. When you're just writing raw data to a medium, how does it know where the file begins and ends? What directory it's inside? When the file was modified? The File System takes care of that. And, weird though it may sound, the bigger the storage size, the more space it takes up. Put in an old 8 MB card, and you'll notice it's almost the full 8 MB, but not quite. It seems like almost no space is taken up because the low percentage used by the File System seems very small with something that small: for example, 2% of 8MB is 164k. Put in a 1 GB card, and suddenly that 2% becomes 20 MB. But it's not as simple as a direct percentage like that. The disk or storage medium is divided up into sectors of a certain size: for example, clusters of 32 KB. No more than one file can go in a cluster, but a file can span across multiple clusters. So if you have a 1KB file in a 32KB cluster, that's 31KB of space that's technically empty, but unusable for anything else. This accounts for most of the wasted space you'll find on any device. I could go into it more, but that's getting deeper into the inner workings of file systems (well, FAT anyway).

[pivaska]

That should explain it. I was thinking that the media used on a card was handled differently than the media in a disk drive. Thanks again.

[JustinGTP]

I think that they should sell media cards with the amount of space that is accessible to the consumer. Therefore, if a 1GB card is really only 975MB, they should have 1.25GB cards and sell them as 1GB. The consumer, at the end of it all, only really cares about how many MBs or GBs they have. :)

-Justin.

[:) 1700 Posts. An uneven milestone. Yay. :)]

[Wiggster]

[:) 1700 Posts. An uneven milestone. Yay. :)]

In celebration, I have a new avatar!

[JustinGTP]

In celebration, I have a new avatar!

How wondrous! And, now, so do I!