level n	Virtual machine Mn, with machine language Ln	←Programs in Ln are either interpreted by an interpreter running on a lower machine, or are translated to the machine language of a lower machine
level 3	Virtual machine M3, with machine language L3	. . .
level 2	Virtual machine M2, with machine language L2	←Programs in L2 are either interpreted by interpretres running on M1 or M0, or are translated to L1 or L0
Level 1	Virtual machine M1, with machine language L1	←Programs in L1 are either interpreted by an interpreter running on M0, or are translated to L0
Level 0	Actual computer M0, with machine language L0	← Programs in L0 can be directly executed by the electronic circuits

level 5	problem-oriented language level
	| | translation (compiler) | |
level 4	assembly language level
	| | translation (assembler) | |
level 3	operating system machine level
	| | partial interpretation (operating system) | |
level 2	instruction set architecture level
	| | interpretation (microprogram) or direct execution | |
level 1	microarchitecture level
	| | hardware | |
level 0	digital logic level

-device level: at this level, the designer sees individual transistors, which are the lowest-level primitives for computer designers.

-digital logic level:

-gates: ea. gate has one or more digital inputs (1 or 0) and computes as output some simple functions of these inputs (and/or)

-register: 1-bit memories can be combined in groups of 16, 32, or 64 to form registers. each register can hold a single binary number up to some maximum.

-microarchitecture level: at this level we see a collection of (typically) 8 to 32 registers that form a local memory and a circuit called an ALU (Arithmetic Logic Unit) which is capable of performing simple arithmetic operations.

-data path: the registers are connected to the ALU to form a data path over which the data flow. the basic operation of the datat path consists of selecting one or two registers, having the ALU operate on them and storing the result stored back in some register.

-microprogram: controls the operation of the data path.

-instruction set architecture level (ISA level): instructions carried out interpretively by the mocroprogram or hardware execution circuits. if a computer manufacturer provides two interpreters for one of its machines, interpreting two different ISA levels, it will need to provide two "machine language" reference manuals, one for each interpreter.

-(hybrid level): also in the ISA level; a set of new instructions; a different memory organization; ability to run two or more program concurrently, and various other features. more variation exists between level 3 designs than between those either at level 1 or level 2.

-operating system machine level: the new facilities added at level 3 are carried out by an interpreter running at level 2 which has been called an operating system. those level 3 instructions that are identical to level 2's are carried out directly by the microprogram, not by the operating system. i.e. some of the level 3 instructions are interpreted by the operating system and some are interpreted directly by the microprogram.

-systems programmers: those whom write interpreters and translators that are intended primarily to support the higher levels (above 3rd level); a definite break from level 3 to level 4.

-assembler: the program that performs the translation at level 2 and lower

-high-level languages: level 5 programs; e.g. c, c++, java, lisp, and prolog; programs written in these languages are generally translated to level 3 or level 4 by translators known as compilers.

-compilers: translators for high-level programs from level 5+ to level 3 and level 4; e.g. programs like java are usually first translated to an ISA-like language called java byte code, which is then interpreted.

-architecture: the set of data types, operations, and features of each level.

-computer architecture: the study of how to design those parts of a computer system that are visible to the programers.