Ada's type system allows you to separate the high-level specification of a type (which models a problem) and its low-level representation (size, alignment, bit/byte order, etc.). The language also requires explicit conversions for two different types even if their underlying representation on the hardware is the same.

Example 1:

   type Byte_Count is range 1 .. 4
     with Static_Predicate => Byte_Count in 1 | 2 | 4;  -- Aspects are Ada 2012

   type Component_Count is range 1 .. 4;

   V1 : Byte_Count      := 3;   --  compiler error: expression fails predicate check
   V2 : Component_Count := V1;  --  compiler error: requires explicit conversion

For these two types I'm not really concerned about how they are represented by the hardware, but I could if I needed to.

Example 2:

Extra constraints added to some pre-defined types:

   subtype String8 is String
     with Dynamic_Predicate => String8'Length <= 8;

   subtype Even_Integer is Integer
     with Dynamic_Predicate => Even_Integer mod 2 = 0,
          Predicate_Failure => "Even_Integer must be a multiple of 2";

Example 3:

Use big-endian for some network packets:

   type Packet_Type is record
      Header : Header_Type;
      Data   : Data_Type;
   end record;

Low-level representation (placed in the private part of a package spec):

   for Packet_Type use record
      Header at 0 range   0 .. 255;
      Data   at 0 range 256 .. 1855;
   end record;

   for Packet_Type'Bit_Order use System.High_Order_First;
   for Packet_Type'Scalar_Storage_Order use System.High_Order_First;
   for Packet_Type'Size use 232 * System.Storage_Unit;