Thursday, May 8, 2014

Why you have ~10% less Hard Drive/USB space than the advertised space on the package?

Why do you have less hard drive / USB drive size in Windows than advertised?

Let's examine this, I recently purchase a USB stick that can hold advertised space of 32Gb of data. 

When I plugged in this USB drive and went to format this drive in Windows, I only get a reported maximum capacity of only 29.7G of space? 

This is an apparent loss of 32-29.7 = 2.3 Gigs of space! Or 6.7% of space gone.
What happened? Where did that extra space go, I didn't do anything yet.

Lets take an in-depth look into the drive info to find out. A cleaver way to do this is to use the MSINFO32.exe (Start->Run->type msinfo32) to run. Goto Components > Storage > Disks and scroll down to the General USB Disk. 

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Here we see in the reported Size is 29.71Gb or (31,905,861,120 bytes) for the USB Drive.

Advertisers are the total bytes number and treating it a normal decimal number.
By their math, dividing by 1000 to get shift of 3 places, results in this 

          31,905,861,120 bytes = 
31,905,861 Kb = 31,905 Mb = ~ 32Gb ADVERTISED

But this is wrong. Bytes is NOT a decimal number. 

How many bits in byte?  Well, there are 8 bits in a byte. Each bit can either 1 or 0. A bit is called binary number. Binary is base 2, whereas decimal is base 10 because it has 10 digits {0,1,2,3,4,5,6,7,8,9}.

So to move a number by 3 places place in binary we have to divide by 1024, which is a standard agreed by International Electrotechnical Commission. 

Let's do the right math, we divide by 1024 to get shift of 3 places.

         31,905,861,120 bytes = 31,158,067.5 Kb = 30,427.8 Mb = 29.71Gb ACTUAL

Windows correctly reports the size of the hard disk/USB Flash Disk drive.

Advertisers are reporting the wrong HD/USB space. Advertiser are wrong math to when calculation Gigabyte sizes. 

So you are are loosing 2.2 Gb ~ 6.7% of space on this 32Gig HD out of the box!

This chart summarizes the amount of lost data because of bad math.

click for larger

As we can see Windows reports the actual HD/USB space correctly, and advertisers are ripping you off.
A class action lawsuit was settle by Western Digital in 2006 over HD size, that's how old this issue is and marketer's are still doing it! Sue my friends, sue.

Here's a logarithmically scaled version from Wikipedia.

click for larger

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