On the Nokia Lumia 530 Dual Sim, as on many other devices, part of the internal memory is reserved for the operating system and system files. This is a common practice to ensure that your device functions properly.

Your phone has 4GB of inbuilt memory, but not all of this space is available for storing user data. Some of the memory is reserved for the Windows Phone operating system, pre-installed applications, and system files.

If you want to free up extra space, you can use the following steps:

Uninstall unnecessary apps:

Check if you have any installed apps that you no longer use and uninstall them.

Clearing temporary files:

In your device settings, look for the "Storage" or "Memory" section.

There should be options there to delete temporary files, cache and other unnecessary data.

Move data to a memory card (if supported):

If your phone has a memory card slot, you can move some of your data (e.g. photos, music) to a memory card, thus freeing up space on the inbuilt storage.

If you are still struggling with space constraints, you may want to consider using a memory card or transferring some of your data to external storage.

There could be several reasons why a portion of your Nokia Lumia 530 Dual Sim's storage is blocked. One possibility is that the operating system and pre-installed apps are taking up a significant amount of space. Additionally, temporary files, cache data, and system files may also contribute to the "other" category, which can consume storage capacity. It's also worth noting that the device's storage capacity is often advertised in terms of raw capacity (4GB in this case), but the actual usable space is typically lower due to formatting and system requirements. Hope that helps!