Should a 2GB memory stick have exactly 2048MB

Dman001

I was looking thriugh ebay for a 2GB memory stick and I saw a few ads said that the available memory is 1.85GB.Is this right?All help appriciated

robinph

They changed the way they count gigs a while ago so that they are a round 1000 now rather than 1024 as they should be, but 1k is still 1024bytes so at some point in calculating the capacity you appear to lose some due to the rounding. You can also loose a bit of the capacity depending on the formatting of the card file system as well. 1.85g sounds about the same as I have on my 2g cards though

steveland?

The filesystem takes up space on the stick. Basically there's 2048Megabytes of space but you're never going to have 2048MB of free space as there needs to be a filesystem on it to read it. Think of it like a cardboard box with a certain amont of space in it. The capacity is read as the entire space taken up by the box but the only space you can use to store stuff is the entire space taken up by the box and the space inside it minus the space taken up by the box itself... if that makes sense.

Zapho

I've found the same with hard disks too. Certain companies advertise say a harddrive with 40,000,000,000 bytes as being 40gb when in reality its 37.25GB.
Its a little bit irritating, but as long as they tell you the exact number of bytes
then you'll be able to work out the gb yourself.

mathias

Im going to post this as this is the exact reason for the difference in reported capacity , its nothing to do with the file system lads !!

Basically Windows uses binary prefix definitions while drive manufacturers use SI prefix definitions

This is from the Wiki on hard disks , and its correct !!

Capacity measurements

Hard disk manufacturers specify disk capacity using the SI definition of the prefixes "mega," "giga," and "tera." This is largely for historical reasons. Disks with multi-million byte capacity have been used since 1956, long before there were standard binary prefixes. The International Electrotechnical Commission (IEC) only standardized binary prefixes in 1999. Many practitioners early on in the computer and semiconductor industries used the prefix kilo to describe 2^10 (1024) bits, bytes or words because 1024 is close to 1000. Similar usage has been applied to the prefixes mega, giga, tera, and even peta. Often this non-SI conforming usage is noted by a qualifier such as "1 kB = 1,024 bytes" but the qualifier is sometimes omitted, particularly in marketing literature.

Operating systems, such as Microsoft Windows, frequently report capacity using the binary interpretation of the prefixes, which results in a discrepancy between the disk manufacturer's stated capacity and what the system reports. The difference becomes much more noticeable in the multi-gigabyte range. For example, Microsoft's Windows 2000 reports disk capacity both in decimal to 12 or more significant digits and with binary prefixes to 3 significant digits. Thus a disk specified by a disk manufacturer as a 30 GB disk might have its capacity reported by Windows 2000 both as "30,065,098,568 bytes" and "28.0 GB." The disk manufacturer used the SI definition of "giga," 10^9. However utilities provided by Windows define a gigabyte as 2^30, or 1,073,741,824, bytes, so the reported capacity of the disk will be closer to 28.0 GB. For this reason, many utilities that report capacity have begun to use the aforementioned IEC standard binary prefixes (e.g. KiB, MiB, GiB) since their definitions are unambiguous.

Some people mistakenly attribute the discrepancy in reported and specified capacities to reserved space used for file system and partition accounting information. However, for large (several GiB) filesystems, this data rarely occupies more than a few MiB, and therefore cannot possibly account for the apparent "loss" of tens of GBs.

The capacity of a hard disk can be calculated by multiplying the number of cylinders by the number of heads by the number of sectors by the number of bytes/sector (most commonly 512). However, the cylinder, head, sector values are not accurate for drives using zone bit recording, or address translation. On ATA drives bigger than 8 gibibytes, the values are set to 16383 cylinder, 16 heads, 63 sectors for compatibility with older operating systems.

Another common error you may see is people saying that you always lose 7% in the conversion from binary prefixes to SI prefixes ,
for todays hard drive capacities that is almost true but does not hold constant all the way , for instance , a Kilobyte is

in binary , 2^10 = 1024 , and in decimal 10^3 = 1000 , so 1000/1024 = 0.976 or a difference of about 2.5%

the percentage rises as the capacity goes up though ,

for instance 30 GB is

in binary , 2^30 or 1,073,741,824 , and in decimal its 10^9 = 1,000,000,000 , so 1,000,000,000/1,073,741,824 = 0.931 or a difference of 7% approx.

It gets worse as you get bigger , a 1 TB drive for instance ,

1TB in binary = 2^40 = 1099511627776 and in decimal = 10^12 = 1,000,000,000,000 , so 1,000,000,000,000 /1099511627776 = 0.909 or nearly 10% ,

so you can imagine the outrage some people will express when they buy their WD TB external drive and find that theres apparently 100GB missing !! ( of course when you understand the numbers there is no missing capacity )

Dman001

So 1.85GB is real?Thanks everyone

ZENER

Nice one mathias, that or an edited version of it should be put in one of the stickies at the top of the page.

ZEN