The PE File format is expressed in terms of a number of common types. In code these are generally realized as an enumeration, typedef or type alias of some sort o help ensure both clarity of code and correctness of use. This additional clarity and type safety is preferred over use of raw primitive types directly as they onvey no real meaning beyond their basic ranges making correct use of the code less obvious and more error prone.

Table Index

Many PE data structures store Index into a particular table index as a field. This table defines the type names used to store the index and which table it is Index into.

Name underlying type Description
StringTableIndex unsigned 16 bit integer Index into the string table (see: StringTables) for more details)
TypeDefTableIndex unsigned 16 bit integer Index into the type definition table
TypeRefTableIndex unsigned 16 bit integer Index into the type reference table
FieldDefTableIndex unsigned 16 bit integer Index into the field definition table
MethodDefTableIndex unsigned 16 bit integer Index into the method definition table
SigTableIndex unsigned 16 bit integer Index into the signature table (see: SignatureBlobs for more details)
GenericParamTableIndex unsigned 8 bit integer Index into the generic params table (OK to use 1 byte index because we won't support more than 255 generic parameters)
MethodSpecTableIndex unsigned 16 bit integer Index into the method specification table

EmptyIndex Constant

Since Index values are used to access members of a table and since (in C, C++, and many other languages) tables are indexed with the first element as index == 0 the value 0 is not useable as a constant to indicate "none" or "null". Thus a dedicated value is used for .NET nanoFramework metadata tables. Any index with the value 0xFFFF is considered the EmptyIndex and this is normally defined as a manifest constant for the entire code base to test against.

Table Kind

The CLR_TABLESENUM enumeration identifies a specific table in the assembly metadata.

Name Value Description
AssemblyRef 0x0000 Assembly reference table
TypeRef 0x0001 Type Reference Table
FieldRef 0x0002 Field Reference table
MethodRef 0x0003 Method Reference Table
TypeDef 0x0004 Type Definition Table
FieldDef 0x0005 Field Definition Table
MethodDef 0x0006 Method Definition Table
GenericParam 0x0007 Generic Parameters Table
MethodSpec 0x0008 Method Specification Table
Attributes 0x0009 Attribute Table
TypeSpec 0x000A Type Specification Table
Resources 0x000B Resources Table
ResourcesData 0x000C Resource Data Blob Table
Strings 0x000D String Blob table
Signatures 0x000E Signature Blob table
ByteCode 0x000F IL Byte Code Stream Blob Table
ResourcesFiles 0x0010 Resource Files Table
EndOfAssembly 0x0011 End of Assembly Table (Used to quickly find the end of the assembly when scanning assemblies)
Max 0x0012 End of enumeration valid enumeration values must be less than this value

Miscellaneous Types

Name underlying type Description
MetadataOffset unsigned 16 bit integer Offset from the start of the IL instruction stream blob data
MetadataPtr pointer to a const byte Pointer to the interior of the IL instruction stream blob data


Many instructions in IL and fields of data structures contain a token. Tokens in IL Metadata reference some other piece of metadata in the assembly. Tokens contain the table the token refers to along with Index into the table into a single primitive integral value. In .NET nanoFramework PE files there are two kinds of tokens MetadataToken and a more compact BinaryToken.

Metadata Token

A metadata token is an unsigned 32 bit value where the Most significant byte is the table kind and the least significant 16 bits are the table index (In .NET nanoFramework PE format a table index is 16bits only thus there are 8 bits of unused data in a MetadataToken)

Binary Token

A Binary Token is a compact form of representing Index to one or more tables. .NET nanoFramework follows the convention specified by ECMA-335 (I I.24.2.66) for coded index where the least significant bits are used to determine which of the possible tables and the remaining bits provide the index of the table entry. Except for a few tags that, because of legacy code, use the most significant bits. Because of it's small size only the 2 bytes version is used. The following table provides the type name aliases for the various combinations of tables used in .NET nanoFramework PE metadata.

TypeRefOrAssemblyRef: (1 bit to encode tag) Tag
AssemblyRef 0
TypeRef 1
TypeDefOrRef: (2 bits to encode tag) Tag
TypeDef 0
TypeRef 1
TypeSpec 2
MethodDefOrRef: (1 bit to encode tag) Tag
MethodDef 0
MemberRef 1
MemberRefParent: (3 bits to encode tag) Tag
TypeDef 0
TypeRef 1
ModuleRef 2
MethodDef 3
TypeSpec 4
TypeOrMethodDef: (1 bit to encode tag) Tag
TypeDef 0
MethodDef 1
FieldRefOrFieldDef: (1 bit to encode tag) Tag
FieldDef 0
FieldRef 1


Many .NET nanoFramework PE data structures include a version. The versions, when presented for readability are typically represented as a quad of 4 integer values separated by a '.' (i.e. the following table defines the Version info structure used in the PE file to represent a version.

Name Type Description
Major unsigned 16 bit integer Major component of the common version quad
Minor unsigned 16 bit integer Minor component of the common version quad
Build unsigned 16 bit integer Build component of the common version quad
Revision unsigned 16 bit integer Revision component of the common version quad


The DataType enumeration corresponds to the ECMA-335 ELEMENT_TYPE_xxxx, however the actual numeric values are not the same as the interpreter uses only a reduced sub-set of the standard values.

Name Description
Void 0 byte void value
Boolean 1 byte boolean value
I1 8 bit signed integer
U1 8 bit unsigned integer
CHAR 16 bit UTF-16 character
I2 16 bit signed integer
U2 16 bit unsigned integer
I4 32 bit signed integer
U4 32 bit unsigned integer
R4 32 bit IEEE-754 floating point value
I8 64 bit signed integer
U8 64 bit unsigned integer
R8 64 bit IEEE-754 floating point value
DateTime 8 bytes - Shortcut for System.DateTime
TimeSpan 8 bytes - Shortcut for System.TimeSpan
String 4 bytes - short cut for reference to System.String
Object 4 bytes - Shortcut for reference to System.Object
Class CLASS <class Token>
ValueType VALUETYPE <class Token>
SZArray Shortcut for single dimension zero lower bound array SZARRAY <type>
ByRef BYREF <type>
Var VAR Generic parameter in a generic type definition, represented as number (new in v2.0)
GenericInst GENERICINST Generic type instantiation (new in v2.0)
MVar MVAR Generic parameter in a generic method definition, represented as number (new in v2.0)