Tutorials - Hardware

HDD Size Deduction Explained

It's because of the way different people calculate what a gigabyte is. The manufacturers will say "Well, that's a 750 GB drive because it has 750,000,000,000 bytes of avaiable storage." Ok, but a GB is in fact 1073741824 bytes (1024 X 1024 X 1024) So Windows reports available space according to actual gigabytes while the manufactures just use 1,000,000,000 bytes to represent a gigabyte.

That means there is around a 7% difference between what the manufacturers say and what an operating system will report... and that's pretty much explains your difference between 750 GB and 700 GB HDD.

Doing the math:
So do you want to try to understand it better? Then we have to do math calculations.
Before we do anything, we have to know some conversions the operating system way. Not the way that manufacturers think!
1GB = 1024MB
1MB = 1024KB
1KB = 1024Byte
1Byte = 8Bits

The only part that manufacturers and operating systems think alike is the conversion between Byte to Bits.

Let's say you have a 1GB Memory stick but it only shows 953MB. So you're thinking then my operating system should only reduce 24MB ONLY and show the total of 976MB. Not exactly! Because all the conversions that has been done between GB all the way down to Byte was 1024. So you are not loosing only 24MB! You are loosing 24MB from each conversion. To get the right amount you have to do the calculations below:

You have to multiply 1GB to 1000, 3 times to get down to bytes. Now this is what manufacturers are calculating. Then you divide 2 times to go up to GB. This is what operating systems are calculating.
Here is the formula:

((((1*1000)*1000)*1000)/1024)/1024 = 953.67431640625

Let's try another one:
Right now I have a 1TB HDD but it only shows 931GB. Now this one has one extra step for both conversions. Because it's TB! Here is the formula:

((((((1*1000)*1000)*1000)*1000)/1024)/1024)/1024 = 931.322574615478515625