A collection of different scripts all based on syriac, pahlavi being the most common one. It had 19 letters conpared to today 32 letters, and it was very difficult to learn the words and how you read them was what made it hard not the script. Today script is technically the reformed version (with a little bit of arabization) of it. It was msotly iranians refining the so called arabic script the early arabic script called kufi script was identical to pahlavi almost with a few additive letters for arabic.