Probation is a supervised program that occurs outs of the prison system after the defendant has been convicted.  Pre-trial intervention, on the other hand, does not actually result in conviction so long as you successfully complete all conditions of the program. In other words, after completing traditional probation, you will be required to disclose a criminal conviction in certain settings, but after successfully completing PTI, there will be no criminal conviction to disclose (although you will have an arrest record, which you may be entitled to expunge after six months).