You’re correct in saying they both use the same protocol (ISO 14443A) for basic structure of communication but that’s where the similarities stop.
ISO14443A is just a standard which broadly defines various things but does not set rules for how specific chips should implement data structure, security, authentication etc.
Think of the protocol (ISO1443A) like language (ie English) and the specific chipset (Eg MFC S50, NTAG213, 215, 216 etc) like dialect (Boston, Southern USA, Totonto, Scouse, Fijian English etc). While each dialect is based on the same language and follow broad concepts, these arent always what is implemented or used by people who speak a specific dialect when conversing.
More specifically comparing Mifare Classic to NTAG21x chipsets, they share a few similarities but also fundamental differences:
| Similar | Differences |
|---|---|
| ISO14443A protocol | Encryption - Crypto1 (MFC) vs no encryption (Ntag21x) |
| 13.56 MHz frequency | Memory layout: sectors/blocks (MFC) vs pages (Ntag21x) |
| Passive, contactless tags | Authentication: key-based (MFC) vs password + lock bytes (Ntag21x) |
| Read/write capabilities | NFC type: Doesnt conform (MFC) vs NFC Forum Type 2 (Ntag21x) |
| No internal power source | Typical usage: Controlled Access (MFC) vs NFC sharing / ID (Ntag21x) |
| Short-range communication | Compatibility: Some phones dont fully support MFC, all NFC phones support Ntag |
If youre looking for more reading, Id recommend looking at the datasheets for both chipsets and understanding how each works before comparing the two.
Hope this helps, not sure if this has explained or clarified much but Im happy to try more should you still have questions.