If Michael Jackson's doctor, Conrad Murray, is convicted of felony involuntary manslaughter and sentenced to the maximum -- 4 years in state prison -- he will not spend a single day in prison and could end up on house arrest.

A new law went into effect in California on October 1, which says, because of overcrowding, people convicted of non-violent felonies cannot be sent to State prison.  Instead, non-violent felons serve their time in county jail.

Law enforcement tells TMZ that involuntary manslaughter is a non-violent felony, which means if Murray is convicted he'd go to L.A. County Jail.

As for how much time Murray would serve, L.A. County Sheriff's officials tell TMZ that Murray would be jailed for half the actual sentence.  So if he gets the maximum -- 4 years -- he would only serve 2. 

But there's a twist, Murray could actually serve way less than 2 years.  Because of severe overcrowding, inmates are eligible for house arrest, based on 2 factors -- their prior criminal history, and risk to the community.  Murray has a clean record and, as one law enforcement official put it, the crime he is accused of means he poses no risk to the public.

So if the jail is filled, the Sheriff could put him on house arrest with an electronic monitoring bracelet.   But one official from the Sheriff's Department told us, Murray wouldn't be placed on house arrest right out of the box.  He would almost certainly do some time before the jailhouse doors would open.