diff --git a/lib/arm/arm_platform.rb b/lib/arm/arm_platform.rb
index 5f3fef0b..7376a238 100644
--- a/lib/arm/arm_platform.rb
+++ b/lib/arm/arm_platform.rb
@@ -10,5 +10,8 @@ module Arm
     def padding
       0x11000 - loaded_at
     end
+    def num_registers
+      16
+    end
   end
 end
diff --git a/lib/risc/block_compiler.rb b/lib/risc/block_compiler.rb
index 9d733690..2f76476f 100644
--- a/lib/risc/block_compiler.rb
+++ b/lib/risc/block_compiler.rb
@@ -1,7 +1,8 @@
 module Risc
 
   # A BlockCompiler is much like a MethodCompiler, exept for it's for blocks
-  # This only changes scoping for variables, lsee slot_type
+  # This only changes scoping for variables, see slot_type
+  # (dynamic resolve, as needed when the block is passed, is not implemented)
   #
   class BlockCompiler < CallableCompiler
 
diff --git a/lib/risc/callable_compiler.rb b/lib/risc/callable_compiler.rb
index bec24927..1cf23485 100644
--- a/lib/risc/callable_compiler.rb
+++ b/lib/risc/callable_compiler.rb
@@ -25,6 +25,7 @@ module Risc
     end
     attr_reader :risc_instructions , :constants , :callable , :current
 
+    # find the return label. Every methd should have exactly one
     def return_label
       @risc_instructions.each do |ins|
         next unless ins.is_a?(Label)
@@ -33,6 +34,7 @@ module Risc
     end
 
     # add a constant (which get created during compilation and need to be linked)
+    # constants must be Parfait instances
     def add_constant(const)
       raise "Must be Parfait #{const}" unless const.is_a?(Parfait::Object)
       @constants << const
diff --git a/lib/risc/interpreter.rb b/lib/risc/interpreter.rb
index 236c5843..13d97b5f 100644
--- a/lib/risc/interpreter.rb
+++ b/lib/risc/interpreter.rb
@@ -29,7 +29,7 @@ module Risc
       @registers = {}
       @flags = {  :zero => false , :plus => false ,
                   :minus => false , :overflow => false }
-      (0...12).each do |reg|
+      (0...InterpreterPlatform.new.num_registers).each do |reg|
         set_register "r#{reg}".to_sym , "r#{reg}:unknown"
       end
       @linker = linker
diff --git a/lib/risc/interpreter_platform.rb b/lib/risc/interpreter_platform.rb
index 69bd93af..e5ad4ec0 100644
--- a/lib/risc/interpreter_platform.rb
+++ b/lib/risc/interpreter_platform.rb
@@ -10,6 +10,9 @@ module Risc
     def padding
       0x100 - loaded_at
     end
+    def num_registers
+      16
+    end
   end
   class Instruction
     def nil_next
diff --git a/lib/risc/platform.rb b/lib/risc/platform.rb
index f305f2b2..2af1a5b4 100644
--- a/lib/risc/platform.rb
+++ b/lib/risc/platform.rb
@@ -13,6 +13,11 @@ module Risc
     # return an integer where the binary is loaded
     def loaded_at
     end
+
+    # return the number of registers the platform supports
+    def num_registers
+    end
+    
     # Factory method to create a Platform object according to the platform
     # string given.
     # Currently only "Arm" and "Interpreter"
diff --git a/lib/slot_machine/block_compiler.rb b/lib/slot_machine/block_compiler.rb
index 3cfba0e0..16c6df47 100644
--- a/lib/slot_machine/block_compiler.rb
+++ b/lib/slot_machine/block_compiler.rb
@@ -1,6 +1,10 @@
 module SlotMachine
 
-  # A BlockCompiler is much like a MehtodCompiler, exept for blocks
+  # A BlockCompiler is much like a MethodCompiler, except for blocks
+  # Blocks are much like methods (hence the base classes) , just the
+  # scope for accessing variables is different. (This only applies to static
+  # blocks, not ones being passed around. That is undone because it needs runtime
+  # code to resolve variables)
   #
   class BlockCompiler < CallableCompiler
 
@@ -16,6 +20,8 @@ module SlotMachine
       "#{@method.self_type.name}.init"
     end
 
+    # Create the risc equivalent, which is a also a (Risc) BlockCompiler
+    # sintructions are converted from slot to risc in instructions_to_risc (in base class)
     def to_risc
       risc_compiler = Risc::BlockCompiler.new(@callable , @method , slot_instructions)
       instructions_to_risc(risc_compiler)
diff --git a/lib/slot_machine/callable_compiler.rb b/lib/slot_machine/callable_compiler.rb
index 13805a4c..f4dd42c7 100644
--- a/lib/slot_machine/callable_compiler.rb
+++ b/lib/slot_machine/callable_compiler.rb
@@ -6,6 +6,9 @@ module SlotMachine
   # - slot_instructions: The sequence of slot level instructions that was compiled to
   #                 Instructions derive from class Instruction and form a linked list
 
+  # Since we have many different compilers, and they are kept in lists, the
+  # Util CompilerList encapsulates the list behaviour
+  #
   class CallableCompiler
     include Util::CompilerList
 
@@ -21,6 +24,8 @@ module SlotMachine
     end
     attr_reader :slot_instructions , :constants , :callable , :current
 
+    # find the return_label, every method should have exactly one (see constructor)
+    # used during return sequence code generation
     def return_label
       @slot_instructions.each do |ins|
         next unless ins.is_a?(Label)
diff --git a/lib/slot_machine/method_compiler.rb b/lib/slot_machine/method_compiler.rb
index 20b9cf98..cb1695a0 100644
--- a/lib/slot_machine/method_compiler.rb
+++ b/lib/slot_machine/method_compiler.rb
@@ -5,6 +5,30 @@ module SlotMachine
 
   class MethodCompiler < CallableCompiler
 
+    # helper method for builtin mainly
+    # the class_name is a symbol, which is resolved to the instance_type of that class
+    #
+    # return compiler_for_type with the resolved type
+    #
+    def self.compiler_for_class( class_name , method_name , args , frame )
+      raise "create_method #{class_name}.#{class_name.class}" unless class_name.is_a? Symbol
+      clazz = Parfait.object_space.get_class_by_name! class_name
+      compiler_for_type( clazz.instance_type , method_name , args , frame)
+    end
+
+    # create a method for the given type ( Parfait type object)
+    # method_name is a Symbol
+    # args a hash that will be converted to a type
+    # the created method is set as the current and the given type too
+    # return the compiler
+    def self.compiler_for_type( type , method_name , args , frame)
+      raise "create_method #{type.inspect} is not a Type" unless type.is_a? Parfait::Type
+      raise "Args must be Type #{args}" unless args.is_a?(Parfait::Type)
+      raise "create_method #{method_name}.#{method_name.class}" unless method_name.is_a? Symbol
+      method = type.create_method( method_name , args , frame)
+      self.new(method)
+    end
+
     def initialize( method )
       super(method)
     end
@@ -30,38 +54,13 @@ module SlotMachine
       risc_compiler
     end
 
-    # helper method for builtin mainly
-    # the class_name is a symbol, which is resolved to the instance_type of that class
-    #
-    # return compiler_for_type with the resolved type
-    #
-    def self.compiler_for_class( class_name , method_name , args , frame )
-      raise "create_method #{class_name}.#{class_name.class}" unless class_name.is_a? Symbol
-      clazz = Parfait.object_space.get_class_by_name! class_name
-      compiler_for_type( clazz.instance_type , method_name , args , frame)
-    end
-
-    def add_method_to( target )
-      target.add_method( @callable )
-    end
-
+    # create a block in the scope of the method.
+    # Blocks are like other constants, exept with code.
+    # They need to be compiled, so a list of them is kept
     def create_block(arg_type , frame_type)
       @callable.create_block(arg_type ,frame_type)
     end
 
-    # create a method for the given type ( Parfait type object)
-    # method_name is a Symbol
-    # args a hash that will be converted to a type
-    # the created method is set as the current and the given type too
-    # return the compiler
-    def self.compiler_for_type( type , method_name , args , frame)
-      raise "create_method #{type.inspect} is not a Type" unless type.is_a? Parfait::Type
-      raise "Args must be Type #{args}" unless args.is_a?(Parfait::Type)
-      raise "create_method #{method_name}.#{method_name.class}" unless method_name.is_a? Symbol
-      method = type.create_method( method_name , args , frame)
-      self.new(method)
-    end
-
     # determine how given name need to be accsessed.
     # For methods the options are args or frame
     def slot_type_for(name)
diff --git a/test/arm/test_arm_platform.rb b/test/arm/test_arm_platform.rb
index 9e141545..fbd7cbb8 100644
--- a/test/arm/test_arm_platform.rb
+++ b/test/arm/test_arm_platform.rb
@@ -14,5 +14,8 @@ module Arm
     def test_platform_loaded_class
       assert_equal ::Integer , @arm.loaded_at.class
     end
+    def test_registers
+      assert_equal 16  , @arm.num_registers
+    end
   end
 end
diff --git a/test/risc/test_interpreter.rb b/test/risc/test_interpreter.rb
index 7d133fd3..93cfe412 100644
--- a/test/risc/test_interpreter.rb
+++ b/test/risc/test_interpreter.rb
@@ -20,7 +20,7 @@ module Risc
       assert_equal :stopped , Interpreter.new(@linker).state
     end
     def test_has_regs
-      assert_equal 12 , Interpreter.new(@linker).registers.length
+      assert_equal 16 , Interpreter.new(@linker).registers.length
     end
     def test_has_r0
       assert_equal :r0 , Interpreter.new(@linker).registers.keys.first
diff --git a/test/risc/test_interpreter_platform.rb b/test/risc/test_interpreter_platform.rb
index ba4e2774..2a6f040e 100644
--- a/test/risc/test_interpreter_platform.rb
+++ b/test/risc/test_interpreter_platform.rb
@@ -17,6 +17,9 @@ module Risc
     def test_translator
       assert IdentityTranslator.new
     end
+    def test_registers
+      assert_equal 16  , @inter.num_registers
+    end
   end
   class TestIdentityTranslator < MiniTest::Test
 
diff --git a/test/sol/send/test_not_found.rb b/test/sol/send/test_not_found.rb
index ffab9cfe..c9e68a5e 100644
--- a/test/sol/send/test_not_found.rb
+++ b/test/sol/send/test_not_found.rb
@@ -1,7 +1,7 @@
 require_relative "../helper"
 
 module Sol
-  class TestSendCachedSimpleSlotMachine < MiniTest::Test
+  class TestNotFoundSlotMachine < MiniTest::Test
     include SolCompile
 
     def setup