Why Advertised Storage Does Not Match Real Data Capacity

This happens with us every time. We buy a hard drive but we never get the capacity as the drive was advertised for. Many consider find this rude. Today I am going to explain how manufacturers rate the capacity of storage drives compared to their actual sizes.

Advertised storage vs. real DATA

Advertised storage vs. real DATA

Bits, Byte and Prefixes

The baseline of storage drives is the binary format in form of zero or one. Eight of these bits combined together produce the commonly referred-to item used in computing which is called byte. Similarly various amounts of storage capacity are generated by this prefix which shows specific amount like a metric prefix. As every computer is based on binary math, so these prefixes generally show base 2 amounts with every level with an increment of 2 to the 10th power of 1,024. The common prefixes are as follow:

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

It’s important because a computer operating system gives report in form of bytes with prefixes. That’s why OS which reports of total space of 70.4 GB would have 75,591,424,409 bytes of storage space.

Advertised vs. Actual

We generally don’t think about the base 2 mathematics, manufacturers decided to rate most drive capacities with 10 base. So 1 GB is equal to 1 million bytes, and 1 TB is equal to 1 trillion bytes. This approximation didn’t gave any problem when Kilogram was used for it, but each level of increase in prefix actually increased the total discrepancy of the space compared to advertised.

Let’s see quickly how the amount of actual value and advertised value are different

Megabyte difference = 48,576 bytes
Gigabyte difference = 73,741,824 bytes
Terabyte difference = 99,511,627,776 bytes

So for every gigabyte about 73,741,824 bytes or 70.3 MB of disk space is over-reported. That’s why when 80GB advertised drive will give you actual disk space of 74.5 GB space which is about 7 percent less.

This varies from drive to drive and storage media market. Consumers need to pay close attention when they get 1 Gigabyte it’s equal of 1 billion bytes. While the flash media storage comes with actual memory amounts. Similarly a 512 megabytes memory card gives complete 512 MB of data capacity. Similarly SSD of 256 GB will give you only 240 GB of space. SSD markets set aside extra room to store the dead cells for binary vs. decimal difference.

Formatted vs. Unformatted

When you buy any kind of storage drive, you need to format it so that you can use it. This process allows the computer to know which bits stored on the drive are related to a specific file. There are several types of drive formats like FAT16, FAT32, and NTFS. A chunk of storage space is allocated for different formatting schemes so that the data can be cataloged enabling the computer or another device to read and write data smoothly.

As soon as you format the drive, the functional storage space will be decreased to the unformatted capacity. It varies depending upon the type of formatting which allows you to store different kind of file system. That’s why the manufacturers cannot quote the formatted size. You will see this issue commonly with flash drives than hard drives.

While buying a computer, hard drive or flash memory, it’s better to read the specifications. Every manufacturer leaves a footnote on the device specifications sheet to show it’s rating which can be helpful for consumer.

Parallel ATA (PATA)
Terabytes, Gigabytes, & Petabytes: How Big are They?

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