2Tb Or Not 2Tb

[The_Munchmaster]

Last trip to Dubai I bought a 2TB WD My Passport portable hard drive to store movies on, as my 1TB drive was almost full.

 

Well the 2TB drive is now almost full, although when I say almost full I mean 1.75TB full because my 2TB drive only has "available capacity" of 1.81TB.

 

So where is the other 190GB of storage?

 

I can understand some of the 2TB storage being used up with pre-loaded software but not 190GB of pre-loaded software!!

[Guest]

It might be because of bad (unusable) sectors on the disc

[radioman]

You think in base 10 but your computer works in base 8. Additionally some is given over to management tables and indexing that grows as you use the disk.

 

Fear not, Mekong will be along with the math that I simply can't be arsed to do at beer o'clock.

[My Penis is hungry]

I've had two of those, both eventually died on me, quite pissed off I was

[Mekong]

Radioman my friend, thank you for volunteering my good self to answer this query but you know me and I am up for a challenge.

 

It comes down to Bits and Bytes

All computer data is stored in binary format as either a one or zero (called a bit). Eight of these bits together are most commonly called a byte. Storage capacity is measured by a prefix to the B (byte) to represent a specific amount, ie K(Kilobyte), M (Megabyte), G (Gigabyte), T (Terabyte) etc. Since all computers are based on the binary system, these prefixes represent base 2 amounts. Each level is an increment of 2 to the 10th power or 1,024.

The common prefixes are as follows:

• Kilobyte (KB) = 1,024 Bytes
  
• MegaByte (MB) = 1,024 Kilobytes or 1,048,576 Bytes
  
• Gigabyte (GB) = 1,024 Megabytes or 1,073,741,824 Bytes
  
• Terabyte (TB) = 1,024 Gigabytes or 1,099,511,627,776 Bytes
  

This is very important information because when a computer operating system or program reports the available space on a drive, it is going to report the overall total of available bytes or reference them by one of the prefixes. So, an OS reporting a total space of 74.51 GB actually has around 80,004,503,306 Bytes of storage space.

Advertised vs. Actual

Since consumers don't think in base 2 mathematics, manufacturers decided to rate most drive capacities based on the standard base 10 numbers we are all familiar with. Therefore, one Megabyte equals one million bytes while one Gigabyte equals one billion bytes. This isn't too much of a problem with fairly small numbers such as a Kilobyte, but each level of increase in the prefix also increased the total discrepancy of the actual space compared to the advertised space.

Here is a quick reference to show the amount that the actual values differ compared to the advertised for each common referenced value:

• Megabyte Difference = 48,576 Bytes
  
• Gigabyte Difference = 73,741,824 Bytes
  
• Terabyte Difference = 99,511,627,776 Bytes
  

Based on this, for each Gigabyte that a drive manufacturer claims, they are over reporting the amount of disk space by 73,741,824 Bytes or roughly 70.3 MB of disk space. So, if a manufacturer advertises an 80 GB (80 billion bytes) hard drive, the actual disk space is around 74.5 GB of space, roughly 7% less than what they advertise.

Based on this an advertised 2TB Drive will have 1,862.65GB of storage minus the on board drivers for the External HDD to communicate with the host machine approx 0.05 TB and the 1.81TB figure is about right. As a rule of thumb base 2 to base 10 is 7% loss and 50GB for Drivers and Communications (0.05%) is about right.

 

I am well passed beer O'Clock, it's a school day for me in the morning. I hope this makes sense

[baa99]

IBM started this mess to advertise their drives. It made their drives seem larger than competitors.

[radioman]

You think in base 10 but your computer works in base 8. Additionally some is given over to management tables and indexing that grows as you use the disk.

 

Fear not, Mekong will be along with the math that I simply can't be arsed to do at beer o'clock.

 

Bwah hah hah, base 8 my fat arse! Meant base 2 of course, getting my bits n bytes mixed up again, told you it was past beer o'clock. In fact it's now past pussy o'clock!