The episode's title, "B.S.O.D", is another computer-referenced title. The meaning is "Blue Screen of Death" - a condition in which a blue screen appears on a Windows computer after it has crashed, because of an error where the system detects that it can't operate safely.
This relates to the risky safety state that The Machine was in where things ended in the season 4 finale.
Cluster made from PS3 consoles to provide infrastructure for The Machine is not something uncommon. These consoles were somewhat widely used by academic, government and private research facilities to build both powerful and cheap (compared to, i.e. Intel Xeon architecture) computing clusters. As of April 1st 2010, with the release of 3.21 firmware, Sony removed the feature that allowed users to install Linux on their consoles, but one may guess that this fact would not pose a challenge to The Machine.
In the flashback where Harold talks to Grace, Grace is walking her dog. In real life the dog belongs to Michael Emerson and Carrie Preston, and is named Chumley.
Detective Fusco refers to Harold Finch as "Mister Peabody." Mr. Peabody, one half of the duo "Mister Peabody and Sherman," is a animated cartoon super-intelligent dog that wears glasses.
An end card states: In memory of our friends / Tommy Heilig / Joel Reynolds / Maciek Malish
Joel Reynolds died on 29 May 2015. He worked as Assistant Art Director on 44 episodes of Person of Interest (2011), and has 5 credits spanning 1998-2015, including 1,245 episodes of All My Children (1970).
Maciek Malish (1962-2015) died on 12 Sep 2015. He worked as Dialogue Editor on 5 episodes of Person of Interest (2011), and has 126 credits spanning 1987-2017. He won two Emmys for outstanding sound editing for The X-Files (1993) in 1996 and 1997. He was nominated for another 10 Emmys over the course of his career, including for his work on the TV series Lost (2004), The X-Files (1993), Millennium (1996), and The Tick (1994).
There is no information about Tommy Heilig, nor is there any information about cause of death for the other two.
Joel Reynolds died on 29 May 2015. He worked as Assistant Art Director on 44 episodes of Person of Interest (2011), and has 5 credits spanning 1998-2015, including 1,245 episodes of All My Children (1970).
Maciek Malish (1962-2015) died on 12 Sep 2015. He worked as Dialogue Editor on 5 episodes of Person of Interest (2011), and has 126 credits spanning 1987-2017. He won two Emmys for outstanding sound editing for The X-Files (1993) in 1996 and 1997. He was nominated for another 10 Emmys over the course of his career, including for his work on the TV series Lost (2004), The X-Files (1993), Millennium (1996), and The Tick (1994).
There is no information about Tommy Heilig, nor is there any information about cause of death for the other two.