Note that there are 2 official versions of the film, the USA version at 2hours 26mins, and the trimmed version at 1hour 55mins - cutting out a lot of incidental stuff but losing much of the ominous feel and slow built up of tension.
After Kubrick's death the long version, now referred to as the extended cut, has become widely available on Blu-ray, 4K and some DVDs (I think it was always the version on Region 1 DVDs), and I recommend this as the one to watch.
For artistic reasons Kubrick shot the film full frame, and it is best viewed without any matting. Unfortunately recent transfers present the film 1:85 (or wider) for a more 'cinematic look'.