Sunday 22 August 2021

The Transcend JetFlash 920 USB drive is fast - but is it legal?

I bought and received a Transcend JetFlash 920 (#Amazon ad link) today which was advertised as USB 3.2 Gen 1 and with a capacity of 128GB - but is it legal?

This is half the depth and length of the SanDisk Extreme!

The first thing I did was test it using FakeFlashTest.exe and thankfully it passed in just 32 seconds.

Next I tested it using CrystalDiskMark and it gave a benchmark figure on my Haswell Asus Z87 PC which was very similar to the more expensive SanDisk Extreme Pro 3.1 128GB drives which I already have.


Both drives were tested when brand new since a used drive, once filled, will be slower due to read/write/erase cycles being needed. Also, my Z87 mainboard is not USB 3.2 Gen 1 compliant but only 3.0.


Transcend JetFlash 920 USB 3.2 Gen 1  128GB       = currently £28 on Amazon (#ad)
SanDisk Extreme Pro USB 3.1 Gen 1 128GB Z880  = currently £42 on Amazon (#ad)

So it looks pretty good value!

The SanDisk USB connector is retractable while the JetFlash has a detachable plastic cap which does not even clip over the opposite end of the drive and usually gets lost within the first day of use!


Now a 128GB drive should have a capacity of 128,000,000,000 or more, shouldn't it?

Well the total decimal unformatted capacities of my 128GB SanDisk flash drives and the Transcend drive are as follows:

SanDisk1 SDCZ880:            128,043,712,512 bytes (119.25GiB)  Last LBA 250,085,375
SanDisk2 SDCZ880:            128,043,712,512 bytes (119.25GiB)  Last LBA 250,085,375
SanDisk3 SDCZ880:            128,043,712,512 bytes (119.25GiB)  Last LBA 250,085,375
SanDisk4 SDCZ88 (old):     128,043,712,512 bytes (119.25GiB)  Last LBA 250,085,375
Transcend TS128GJF920:    123,718,336,512 bytes (115.22GiB)  Last LBA 241,637,375

So the Transcend is advertised as 128GB but is actually 123.7GB - so we have paid for 4GB that we don't get!

Reviews on Amazon also show that others have noticed the less-than-advertised capacity on their JetFlash 920 USB drives too, so this is not just a one-off occurrence.

The Transcend FAQ says:

Why is the actual storage capacity of my JetFlash USB Flash drive slightly less than the volume specified on the product's package?

All storage products will display less than stated memory capacity on a computer. The discrepancy results from different algorithms. 

On a computer, 1GB = 1024*1024*1024 = 1,073,741,824 (1024 is 2 to the power of 10, which is the algorithm used by the computer) 

For a 16GB JetFlash, the computer will calculate it as having capacity of 14.90GB.  

16,000,000,000÷1,024÷1,024÷1,024 ≒ 14.90GB. 

Also note that each Flash memory may possess innate variances because of its manufacturing process. Transcend will therefore adjust the available space on the JetFlash to store necessary firmware configurations or system data. Please be assured that we do so at appropriate measures and that your JetFlash has the normal capacity. 

Isn't this against the UK 1968 Trades Description Act? Can you really call a product '128GB' but it only has 123.7GB of usable memory?  What if you bought a new car advertised as having a 2.2 litre engine but actually it had only a 2.0 engine - or if you bought 1 litre of  Vodka but it only contained 970ml of Vodka instead of 1000ml?

And, where has the missing 13,720,616,960 bytes of memory gone (137,438,953,472-123,718,336,512)? Surely it can't all be reserved as spare blocks and housekeeping space? Does this mean that it already had a lot of failed bad blocks which needed to be mapped out?

Some SSD drives with 128GiB of memory are sold as '120GB' because they reserve extra blocks as spares and the unformatted capacity is < 128GB so they call it '120GB' - so why not in this case also?


I have been using SanDisk Extreme Pro drives for many years and they have never let me down.
Since I just received the JetFlash today, I will have to let you know how it goes...


I have found that Strelec WinPE does not detect this USB 3.2 drive (but does detect all other 3.1 USB drives) when using a USB 3 port. Therefore it is not as compatible as older USB 3.1 or USB 3.0 drives.

P.S. There was a usb 3 driver missing from the strelec winpe. The latest strelec iso has been fixed.

This problem can be avoided if you boot from the USB drive using a USB 2 Male/Female extension cable to force it to use USB 2.

There may also be other similar situations in WinPE or Linux distros where USB 3.2 is not supported???

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