Different flash drives always have a capacity below what is said to be its memory capacity. A 2GB flash drive will always have a capacity of between 1.7GB and 1.8GB. I have two '4GB' flash drives which have storage capacities of 3.68GB and 3.72GB respectively.

On the other hand, the storage capacity of a computer's HDD is always what the manufacturer called it.

Why can't a flash drive have the storage capacity written on it?

Am yet to find a storage device that's exactly the description size, its always below, even my ps3 storage size, the thing is the hard drives are numbered binericaly.

It has to do with the numbering system. Some computer components (including hard disk)use the binary system of numbering where 1024bytes equals 1Kbyte but in decimal numbering, 1Kbyte is 1000bytes. The difference in size is a function of this 24bytes difference on every Kilobyte. I hope you understand.

tessyade: It has to do with the numbering system. Some computer components (including hard disk)use the binary system of numbering where 1024bytes equals 1Kbyte but in decimal numbering, 1Kbyte is 1000bytes. The difference in size is a function of this 24bytes difference on every Kilobyte. I hope you understand.

Thanks for your response. I got what you're saying. If the decimal numbering is used, a 4GB flash will have 4 X 1000MB=4000MB but since the computer accesing it uses the binary numbering (1GB=1024MB), that same flash will have a storage capacity of 3.90GB (4000/1024MB). I believe I got your explanation right.

However, if what you said is the cause, then every 4GB flash should have a storage capacity of 3.90GB. The case where two 4GB flash drives from different manufacturers have different storage capacities would never have occurred. And I'm yet to see a 4GB flash that has a storage capacity of up to 3.90GB (its always lesser).

In addition to my original post, I've also observed that there is a difference between the storage capacities of a flash drive and a memory card said to be of the same capacity (say 4GB) from the same manufacturer.

Further to what @tessyade said, every memory device reserves certain amount of space for journaling/partition table. These reserved space is typically inaccessible to the user and the amount reserved is dependent on the format of the partition (FAT32, NTSF, ext4 etc). Thats why when you just newly format a drive, with no files on it, you see the available space is already depleted.

The difference in capacities is due to two different methods for defining what exactly the prefixes mega, giga, tera mean. In the computer world, these prefixes have different meanings depending on what exactly you are talking about. Hard drive manufacturers report the size of hard drives using the decimal definition of these terms (10^6, 10^9, 10^12 resepctively), whereas operating systems and other software use the binary definition of these terms (2^20, 2^30, 2^40).

As you can calculate, these values are close, but not exactly the same. 10^6 is 1,000,000, but 2^20 is 1,048,576. Once we get to larger hard drive sizes, the difference really becomes noticeable.

One gigabyte in binary is 1,073,741,824 bytes (2^30), but in decimal it’s only 1,000,000,000 bytes (10^9), which is a difference of 73,741,824 bytes (~70MB). So, when we're talking about storage size in gigabytes a hard drive's capacity as reported by the OS will be about 7.2% less than what is advertised by the hard drive manufacturer.

So for example, what we're buying is not a 500 Gigabyte hard drive, but rather a ~500 billion byte drive. A true 500 GB hard drive would be ~536.87 billion bytes. To know what the actual size your drive is, to the computer, multiply the advertised capacity by 7.2% i.e a 500Gb drive would be: 500 - (500 x 0.072) = 464Gb (in real binary as a computer would see it)

source: Why Is My Hard Drive Capacity Lesser Than Advertised

Maleeq: Further to what @tessyade said, every memory device reserves certain amount of space for journaling/partition table. These reserved space is typically inaccessible to the user and the amount reserved is dependent on the format of the partition (FAT32, NTSF, ext4 etc). Thats why when you just newly format a drive, with no files on it, you see the available space is already depleted.

source: Why Is My Hard Drive Capacity Lesser Than Advertised

Thanks for the insight. My point still remains that if the difference in binary and decimal numbering is the sole cause of this disparity, then every 500GB HDD and 4GB flash should have storage capacities of 464GB and 3.72GB respectively but this obviously is not the case.

I have attached a picture showing the properties of my two 4GB flash drives (from the same manufacturer and with the same partitioning format FAT32) with different storage capacities.

Well, guess the manufactures trick people out of bits. They figure both are still approximately 4Gb!

But are the models of the drives the same? You know possibly different memory components were coupled together for the drives.

^^^^^ No, they are not the same model.