The High Sheriff of Berkshire, in common with other counties, was originally the King's representative on taxation upholding the law in Saxon times.
The title of High Sheriff is therefore much older than the other crown appointment, the Lord Lieutenant of Berkshire, which came about after 1545.
Between 1248 and 1566, Berkshire and Oxfordshire formed a joint shrievalty (apart from a brief period in 1258/1259).
Unlike the Lord Lieutenant of Berkshire, which is generally held from appointment until the holder's death or incapacity, the title of High Sheriff is appointed / reappointed annually.
(From 3 November 1258 to Michaelmas 1259, Nicholas de Hendred was sheriff for Berkshire only.)