A Code Segment Descriptor is used to reference the Code in a CodeFile.

It is created as an entry in the Segment Dictionary by the compiler with a Tag 3 and it contains the Segment Address and the Size in Words of the Code Segment.

Tag 3 - SegDesc
Field	Name	Description
[39:20]	SizeF	Size of the Code Segment in Words
[19:20]	AddressF	The Sector Address in the Codefile of the start of the Code Segment.

A PCW contains a Segment Dictionary Index (SDI) of a Segment Descriptor which describes a Code Segment.

The PCW contains a Word Index (PIR) of 13 bits and a Syllable Index (PSR) of 3 bits and they reference a Code Syllable in the Code Segment.

Since the PIR field is 13 Bits,  a Code Segment is limited to 8191 Words (273 Sectors).

The BRxx Branch Operators also contain a PIR of 13 bits.