Why is a 4TB drive only 3.63 TB?
When it comes to purchasing a new hard drive, it’s essential to understand the technology behind how storage capacity is measured and what factors might affect its actual usable capacity. Unfortunately, many people are baffled when their 4TB drive doesn’t yield the full 4 terabytes of storage they thought they were buying.
The Anatomy of Digital Storage
What Is a Terabyte?
A terabyte (TB) is an SI unit of digital storage, equivalent to 2^40 (1 billion) bytes, or about 1,000 gigabytes (GB). Most modern file systems, like NTFS, HFS+, XFS, JFS, and ext3, use a unit of addressable storage that is even smaller than bytes, referred to as a minimum physical block or, in some systems, simply as a block size. Common block sizes include 4,032 bytes (sectors); 8,192; 16,384 or 32,768 in older systems like FAT systems; and so on
Why a 4TB Drive Doesn’t Reveal Its Entire Capacity: A Marketing Truth
Another significant factor in the digital storage world is the division of storage between the primary and secondary systems. Both have their separate purposes:
| Storage Type | Purpose | % of Total Capacity |
|---|---|---|
| Primary Storage | Run operating system and applications, | 80%, approximately |
While a 4TB disk might be large enough, its actual size is about 3.63TB due to different factors mainly based on technology and space efficiency. We will understand why this may happen:
- Byte to Kilobyte Formula
We know every hard drive capacity is rounded off to be more noticeable, but for instance:
1 TB = 931,330,000 Bytes
We can take the time to understand 4 bytes (or less) space left for additional data types in the header of different blocks. With this process, we reach the ultimate limit of actual storage at 3,630 GB, which roughly translates from 3.63 TB.