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The account of USB Drive’s capacity
Key Word ：FLASH Memory , BLOCK , FAT
Flash memory is a solid-state, non-volatile, rewritable memory（NAND FLASH） that works like RAM and a hard-disk drive combined. Flash memory stores bits of electronic data in memory cells, just like DRAM and SRAM, but flash also works like a hard-disk drive because when the power is turned off, the data stays in memory. Flash memory is becoming increasingly popular for portable computing and communications applications.
By the original manufacturer design, The Flash memory make up of block. For example,128MB can be divided with 1024 blocks ,as the follow：
vided with 1024 blocks ,as the follow：
128Mbyte divided 1024 blocks ,and 1 block divided with 64 page
1 Page divided with 2K+64 bytes
But manufacturers use the account is that 1M =1000 M ,1K=1000Byte .
By this account，The capacity of 128MB can be accounted as follow ：
128MB = 1024（block）*64（page）*2000（byte）=131072000 bytes
As we know the computer use bytes as a unit to account disks capacity.
The computer use the account is that 1MB=1024K 1K=1024Byte
By this account，128M=1024*1024=1311768576 bytes. that we see the actual capacity is
131072000/（1024*1024）=125MB
But in fact，there are bad block in product process. A few bad block can be allowed. But the bad block can’t be used，Bad blocks will be deducted from the 1024 good blocks. As hard disk, USB drive also uses FAT or FAT32 file system. FAT file system include MBR main boot partition，FAT file config table and ROOT directory. There will use a few capacity，several Kilo Bytes as general .(The capacity is more larger the lost capacity )，while USB controller will use 10 blocks as spare space for bad block of future using. In order to sure the stability of products, most big manufacturers (such as Toliba, SONY, ect.) always keep above 10 blocks to ensure the stability. The capacity of 125MB will be occupied 1~5M because of above reason. The capacity of 128M Flash memory is impossible to show on computer as 128MB(1311768576 byte).
The hard disk manufactures (as MAXTOR，WESTWOOD，HATACHI) all use the same way to account the capacity. A 80GB hard disk, the actual capacity of 76GB only.
Below is the capacity standard of Tripower:
64M—60M
128M-120M
256M-240M
512M-475M-485M
1GB-960M-975M
2GB-1800M-1900M, show in computer is 1.75G-1.85G
4GB-3800M-3842M, show in computer is 3.7-3.75G
8GB-7600M-7900M, show in computer is 7.4-7.75G
16GB-15155M-16076M, show in computer is 14.7G-15.7G
"Upgrade" means using lower capacity flash memory upgrade to higher capacity flash by software.
For example, use 256MB can upgrade to any higher capacity as 512MB,1GB,2GB,4GB,8GB,16GB or more. When customer buys the upgrade flash memory drive, the real capacity is the lower flash capacity.
For example, when customer buys a 1GB upgrade to 8GB flash drive, the real capacity is 1GB only. When customer plug the drive into their computer, they will see the disk shows 8GB. If they store the data more than the real capacity 1GB, the more part than 1GB will be stored in the disk of the computer. If they plug the drive into their computer again or into another computer, the data which more than 1GB will be lost.
The best way to try if your USB Flash Drive is a full capacity drive or not, you could store full capacity data which the drive shows, and then take it to another computer. If it lose some data, then it's an upgrade flash drive or a drive with not full capacity.
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