USB drives larger capacity than advertised?

[jtr1962]

I thought this might be of some general interest. We've all been buying USB drives for a long time. Usually their capacity seems to be exactly as advertised, or sometimes a slight amount less. For example, I have a pair of these I bought last year which are 127,968,411,648 bytes total capacity-a bit less than 128 decimal GB but still very close. Last week I bought two of these. One had 133,143,953,408 bytes and the other 137,019,490,304 bytes. What I think accounts for the differences is the nature of flash memory chips. They're made in powers of two, so 128 GB drives really have chips with 128 binary GB, or 137,438,953,472 bytes, of raw flash memory. At the factory they test all the cells, lock out the defective ones, and keep some percentage as spares. I guess in the case of my two new PNY drives the flash memory tested better than expected, so rather than locking out a lot of perfectly good memory, they left it accessible to the user.

Has anyone else experienced this? Obviously it's great to get more than you paid for. I'm just wondering how often it happens.

 

[LunarMist]

Has anyone else experienced this? Obviously it's great to get more than you paid for. I'm just wondering how often it happens.[/FONT]

I don't really notice USB flash drive capacities, but high end memory card free capacity is consistently lower than the maximum. Usually the 32GB cards are about 29.8, 64GB are about 59.6, and so forth.
I assume they have some space reserved for mapped bad cells and reserved areas for future bad cells. The firmware for the controller is probably only a few MB and would not show at the GB level.

 

[time]

Lunar, storage has been measured in billions of bytes (Gigabytes or GB) for many years now - except in brain-dead Windows, which never quite got past the days of MS DOS.

Windows displays binary gigabytes, i.e. GiB, which is actually only relevant to RAM because each word/dword is directly accessible through binary address lines. Mass storage has (almost) never worked that way.

So multiply storage capacity by 0.9313 if you want to see what Windows will show (I haven't checked to see if this is still the case with Windows 10).

 

[Stereodude]

I can't say I've ever noticed one exceeding the listed size. They've always been smaller (due to the base 10 vs base 2 thing).