Capacity of Storages

[life24]

Hello,
I have flash disk and memory RAM and ... .
When i bought 4 GB flash disk,I can used 3.75 GB . Why?
4 Gb * 1024 = 4048 MB
How calculated?

 

[LTC8K6]

Some space is used by the file system, and there are different ways to define "gigabyte".

 

[life24]

Some space is used by the file system, and there are different ways to define "gigabyte".

Thank you,
Can you more explain about this?

Some space is used by the file system

and there are different ways to define "gigabyte".

 

[LTC8K6]

4,028,600,320/1,073,741,824=3.75

Correct.

Plus the file system structure takes up space on the drive, so you can't use the whole capacity. The drive itself needs some storage.

This is true for all drives.

https://en.wikipedia.org/wiki/Gigabyte

 

[Nec_V20]

Hard, Flash and SSD drive capacity are always measured in powers of 10 (GigaBytes) and not powers of 2 (GibiBytes) as is the case with RAM.

Four GigaBytes of your flash drive are 4*10^9 whereas four GibiBytes of RAM would be 4*2^30.

 

[Red Squirrel]

Manufacturers define GB by 1KB = 1000 byte, which, on regular metric system is technically right, but in computers, it's not, it's 1024. So for every KB of the advertised storage you lose 24 bytes. It adds up.

ex:

1TB = 1024 * 1024 * 1024 * 1024 = 1,099,511,627,776 bytes

But manufacturers will say that:

1TB = 1000 * 1000 * 1000 * 1000 = 1,000,000,000,000 bytes

So take 1,000,000,000,000 and convert to real GBs: (because 1TB advertised by manufacturer is less than a real TB)

1,000,000,000,000 divided by1024 3 times = 931.3GB

When you get into 10TB+ raid arrays it really starts to add up. This is something to take seriously if sizing a large SAN for example. To make matters worse with SANs is that the vendor will not count raid either. A 10TB SAN might end up being like 4TB of actual usable space. Say you decide to go with a single raid 10 lun you are already down to 5TB, but remember that 1TB = 931GB from our calculations so the SAN ends up being about 4.5TB. When I worked at a hospital this is a mistake the ones responsible for sizing the SAN did. 60 grand later we still did not have enough space.

But back to your USB stick, the same calculations I shown above work out 3.73GB so it seems to be in the same ball park.

It's 4:44 am, so hopefully my math is not off. 😛

 

[Essence_of_War]

Manufacturers define GB by 1KB = 1000 byte, which, on regular metric system is technically right, but in computers, it's not, it's 1024. So for every KB of the advertised storage you lose 24 bytes. It adds up.

I just want to add that it is not just the manufacturers, and that defining a KB/MB/etc in this way isn't completely crazy. The metric system existed long before modern commodity hardware, and the SI unit prefixes are used correctly by the hard drive manufacturers, largely because it would be even crazier for metric prefixes to be powers of ten in some situations and be binary powers in computer contexts, but I'm sure the fact that it allows the manufacturer to advertise more capacity doesn't hurt!

When i bought 4 GB flash disk,I can used 3.75 GB . Why?
4 Gb * 1024 = 4048 MB
How calculated?

The terms kibi/mebi/gibi abbreviated by KiB/MeB/GiB can be used to unambiguously represent the binary powers, but most consumers either don't know that or don't care so the manufacturers stick with the metric prefixes. Depending on what OS and system utilities you use, you can use either definition. Consider GNU df, "df --human-readable" will give free disk space in metric powers, while "df --si" will give the same information in binary powers:

~$ df --human-readable
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              29G   22G  5.7G  80% /

~$ df --si
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              31G   24G  6.1G  80% /

The standard windows utilites use binary powers, so that mismatch between the manufacturer who advertises using the standard metrix prefixes and your windows utilities which use binary powers is often the cause of the "where is my disk space!" confusion.

When you get into 10TB+ raid arrays it really starts to add up.

Verily! One can show that the discrepancy is actually a semilog!

1KB / 1 KiB = 1000/1024 = .976
1MB / 1MeB = (1000/1024)^2 = .976^2 = .954
1 GB / 1 GiB = (1000/1024)^3 = .976^3 =.931
1 TB / 1 TiB = (1000/1024)^4= .976^4 =.909
1 PB / 1 PiB = (1000/1024)^5= .976^5 =.888

 

[dbcooper1]

Hello,
I have flash disk and memory RAM and ... .
When i bought 4 GB flash disk,I can used 3.75 GB . Why?
4 Gb * 1024 = 4048 MB
How calculated?

It's even worse than you thought; 4 * 1024 = 4096 not 4048.

 

[razel]

If your flash drive is from a reputable company not wanting to get sued in the U.S., then somewhere on the packaging is the disclaimer that they represent GB as 1,000,000,000 (base 10) not 1,073,741,824 (base 2).

 

[Puffnstuff]

This is something that needs regulation so that the definition of capacity is the same for all manufacturers so as not to confuse the buying public when they look at capacities. This is exactly why windows reports a lower capacity for storage than the manufacturer claims for a given drive. Hence manufacturer A sells a drive with a capacity of 1.5tb and when the customer gets home with it and installs it into their system windows reports a capacity of 1.36tb which confuses them. A single storage standard needs to be implemented so that a drive and OS manufacturer are using the same standard and reporting the same sizes for a given product. This oversight has been long ignored and needs to be addressed by a common standard for measurement just like SAE did with horsepower ratings. Until all manufacturers used the same standard you couldn't compare apples to apples and figures were all over the place.

 

[dave_the_nerd]

This is something that needs regulation so that the definition of capacity is the same for all manufacturers so as not to confuse the buying public when they look at capacities. This is exactly why windows reports a lower capacity for storage than the manufacturer claims for a given drive. Hence manufacturer A sells a drive with a capacity of 1.5tb and when the customer gets home with it and installs it into their system windows reports a capacity of 1.36tb which confuses them. A single storage standard needs to be implemented so that a drive and OS manufacturer are using the same standard and reporting the same sizes for a given product. This oversight has been long ignored and needs to be addressed by a common standard for measurement just like SAE did with horsepower ratings. Until all manufacturers used the same standard you couldn't compare apples to apples and figures were all over the place.

Speaking of Apple, OS X and a couple of linux distros now report KB/MB/GB now and not KiB/MiB/GiB. So it does seem like there's a push to standardize, even if it's conveniently on the numbers that "look" bigger.

 

[Essence_of_War]

Speaking of Apple, OS X and a couple of linux distros now report KB/MB/GB now and not KiB/MiB/GiB. So it does seem like there's a push to standardize, even if it's conveniently on the numbers that "look" bigger.

Yup, as I mentioned above, GNU and BSD df/du/ls report whichever way you'd prefer, and OSX's disk utility defaults to metric on all recent versions. Really, I think it's just Windows that does the binary-or-gtfo.