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# CRC verse Checksum Verification for USB Flash Drives

This is a slideshow which explains the difference between verification methods best used for USB flash drives. The two methods being compared are CRC verification (cyclical redundancy check) and Checksum verification. Good information to have if you care about the accuracy of data to USB flash drives.

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### CRC verse Checksum Verification for USB Flash Drives

1. 1. CRC VERSE CHECKSUM VERIFICATION FOR USB FLASH DRIVES
2. 2. Is Checksum or CRC better for checking data written to USB flash drives?
3. 3. SHORT ANSWER CYCLICAL REDUNDANCY CHECK OR CRC Best method for checking data written to a USB flash drive
4. 4. MANY BELIEVE CHECKSUM Best method to verify data written to a flash drive
5. 5. CRC IS BEST Easier to understand how the verification works Easier to implement
6. 6. There are flaws in checksum verification and therefore not suitable for verification of data written to a flash drive
7. 7. WHAT IS THE DIFFERENCE BETWEEN CHECKSUM AND CRC VERIFICATION?
8. 8. CHECKSUM CRC Uses addition in its math calculations to check whether all data was written correctly CRC uses long division in its math calculations to check whether all data was written correctly
9. 9. I am talking about binary long division, not the school-yard long division
10. 10. CHECKSUM Calculate the total bits in a packet of data and include that total checksum amount when the data is sent over communication lines The receiver will then look at the packet, read the checksum value and then perform the same calculation to make sure everything adds up If the calculation on the receiver’s end matches the value passed in the packet, all is good
11. 11. The problem is a high probability that somewhere between the sender and receiver the bits of data are changed, corrupted or swapped yet still turn a correct checksum value after calculation on the receiving end
12. 12. CRC Cyclical Redundancy Checking is about as straight forward as addition but using long division The advantage with this approach is looking throughout the entire packet to verify if all the information arrived correctly As with traditional long division, binary division works through the dividend number from the divisor number
13. 13. Cyclical Redundancy Check Calculations are long division calculations for a packet of information but have just a slight bit of tweaking TO START THE CALCULATION Divisor number is set or “given.” Add in zeros that are one less than the divisor number
14. 14. FOR EXAMPLE If the divisor number is 5 digits long, then you would add four zeros at the end of the packet Calculation would then start for binary long division
15. 15. Now if the calculation swaps the remainder number with the four zeros mentioned above (when the calculation first started), then when the long division is ran again, there is no remainder (remainder is zero) Using this method means all bits in a packet are examined during the binary long division process after the data packet is received
16. 16. Study the two charts below, then it will make sense
17. 17. When it comes to the reason for verification methods to be employed for data transmission it is typically done because of “noise” on the transmission lines
18. 18. Poor design of the electrical part Noise on a transmission line can be encountered for many reasons Not grounded properly Poor quality materials used in the device Source: Thank you Nexcopy Inc. engineers for taking a technical topic and presenting in a non-technical way
19. 19. By using dependable verification methods, the receiver can, more reliably, determine if all the data was sent and received correctly