function Read(
    var VBuffer; 
    ACount: Longint
): Longint; override;

Longint - Number of bytes actually read in the operation.

Read is an overridden Longint method that isolates the platform-specific stream methods required to implement read operations. Read relies on the method implementation in a descendant classes for the protected virtual abstract IdRead method. 

On the .Net platform, Read uses an array of Byte to represent the Buffer for storing values read from the stream. 

On all other platforms, Read uses an untyped pointer to represent the Buffer for storing values read from the stream. Read calls the Move procedure from the Runtime library to update Buffer with the read values. 

Use Write to output values to a platform-specific stream implementation. 

Use Seek to reposition a platform-specific stream implementation.