There are several reasons why two seemingly identical 5TB hard drives might show a different available space of around 900GB. Here are some potential explanations

 There are several motives why  seemingly equal 5TB hard drives may display a unique available space of round 900GB. Here are a few potential causes:

1. **File System Overhead:**

   - The file device used at the tough pressure (e.G., NTFS, FAT32, exFAT) can result in some overhead, the use of a small amount of area for machine systems, metadata, and other internal purposes. This overhead can range among record structures and have an effect on the to be had garage.

2. **Formatting Differences:**

   - If the 2 drives were formatted with extraordinary allocation unit sizes or cluster sizes all through the formatting method, it can lead to variations in the quantity of area used for storing file metadata and handling report allocation.

3. **Hiddetical for the functioning of the file gadget or the operating device.

4. **Reserved Space:**

   - Some running structures reserve a positive quantity of space for device functions, inclusive of paging, hibernation, or device restore factors. This reserved space won't be a part of the user-accessible storage.

5. **Drive Formatting Tools:**

   - The gear used for formatting the drives or coping with partitions may additionally allocate area differently. For example, if one pressure changed into formatted using a specific device or with distinctive settings than the alternative, it is able to result in variations in available space.

6. **Manufacturing Variations:**

   - While unusual, there may be versions in the real capacity of tough drives due to manufacturing variations or defects. Two drives labeled as 5TB may have a mild difference in their real ability.

7. **File Compression or Encryption:**

   - If file compression or encryption is enabled on one power and no longer on the opposite, it may affect the quantity of area documents occupy. Compressed or encrypted files may additionally absorb less or more area depending at the content material.

8. **File System Quotas:**

   - Some record structures help user quotas, limiting the quantity of space man or woman customers or groups can use at the force. If quotas are in place, they could have an effect on the available space.

To inspect the unique variations, you may use file machine tools, disk control utilities, or 0.33-party software program to investigate the file gadget, partitioning, and area allocation on every pressure. Keep in thoughts that the distinction in available space can be because of a combination of the elements cited above.