This .NET class wraps the AcDbXrecord ObjectARX class. 

The Xrecord class is a data storage class that was implemented primarily to allow ADSRX and AutoLISP programs a means to store data in pieces larger than the xdata's 16KB-per-object limit. Each Xrecord object is capable of storing up to 2GB. By establishing an object's extension dictionary as the xrecord's owner, it's possible to associate large amounts of data with that object. 

The input or output mechanism for the data is via a linked list of resbuf structures very similar to the way xdata is accessed on objects. Unlike xdata, however, xrecords work with the standard AutoCAD group codes, which are all below 1000 in value. All the standard AutoCAD group codes are supported. This means that, in addition to all the normally used data types, an xrecord is capable of storing object IDs in any of the four types (hard owner, soft owner, hard pointer, soft pointer) which allows xrecords to own other objects, including other xrecords.

Autodesk.AutoCAD.DatabaseServices.DBObject
    Autodesk.AutoCAD.DatabaseServices.Xrecord

Public Class Xrecord
Inherits DBObject
Inherits IEnumerable

public class Xrecord : DBObject, IEnumerable<TypedValue>;