TL;DR: WD82PURX and WD82PURZ have similar specifications, but are intended for different regions. WD84PURZ is a lower RPM part number.
WD has introduced so many different part numbers lately that it's hard to keep track. Here is a quick comparison of the different part numbers
| Attribute | WD82PURX | WD82PURZ | WD84PURZ |
| Cameras Supported | Upto 64 HD | Upto 64 HD | Upto 64 HD |
| AI Streams | 32 | 32 | - |
| Max Suistained Transfer rate | 245 MB/s | 245 MB/s | 194 MB/s |
| Cache | 256 MB | 256 MB | 128 MB |
| RPM | 7200 | 7200 | 5640 |
| MTBF | 1.5 M Hours | 1.5 M Hours | 1.0 M Hours |
| Warranty | 3 Yrs LTD | 3 Yrs LTD | 3 Yrs LTD |
| Power Average RW | 8.6 W | 8.6 W | 6.2W |
It is not uncommon to have a surveillance drive with low RPM. Since both power consumption and vibration are low on low RPM drives, they tend to be more reliable, albeit with lower transfer rates.
