[SSD Basic] My new SSD shows less capacity than advertised. Why?

This is a very common observation and is entirely normal. There are two primary reasons:

Decimal vs. Binary Measurement (Marketing vs. OS Calculation):
- Manufacturers (Decimal): SSD manufacturers define a kilobyte (KB) as 1,000 bytes, a megabyte (MB) as 1,000,000 bytes, and a gigabyte (GB) as 1,000,000,000 bytes (powers of 10). So, a 1TB drive is advertised as 1,000,000,000,000 bytes.
- Operating Systems (Binary): Computer operating systems (Windows, macOS, Linux) calculate storage using powers of 2. So, a kibibyte (KiB) is 1,024 bytes, a mebibyte (MiB) is 1,024 x 1,024 bytes (1,048,576 bytes), and a gibibyte (GiB) is 1,024 x 1,024 x 1,024 bytes (1,073,741,824 bytes).
- The Discrepancy: When your OS reports a 1TB drive, it's actually displaying it in GiB. So, 1,000,000,000,000 bytes / (1,024^3) ≈ 931.32 GiB. This is why a 1TB SSD typically shows around 931GB of usable space.
Over-Provisioning (OP) and Firmware Space: As discussed in Question 6, a portion of the SSD's raw capacity is reserved by the manufacturer for firmware, over-provisioning, and bad block management. This space is essential for the drive's performance, endurance, and reliability but is not accessible to the user.