Here’s what a program-fragment looks like:
z = x + y;
Native to a processor: executed directly by hardware
Instructions consist of binary code: 1s and 0s
A programming language that uses symbolic names to represent
operations, registers and memory locations.
Slightly higher-level language
Readability of instructions is better than machine language
One-to-one correspondence with machine language instructions
Assemblers translate assembly to machine code
Compilers translate high-level programs to machine code
Either directly, or
Indirectly via an assembler
Software tools are needed for editing, assembling, linking,
and debugging assembly language programs
An assembler is a program that converts source-code
programs written in assembly language into object files in
Popular assemblers have emerged over the years for the
Intel family of processors. These include …
TASM (Turbo Assembler from Borland)
NASM (Netwide Assembler for both Windows and Linux), and
GNU assembler distributed by the free software foundation
In assembly language, mnemonics are used
to specify an opcode that represents a
complete and operational machine language
instruction. This is later translated by the
assembler to generate the object code. For
example, the mnemonic MOV is used in
assembly language for copying and moving
data between registers and memory
Each command of a program is called an instruction (it
instructs the computer what to do).
Computers only deal with binary data, hence the
instructions must be in binary format (0s and 1s) .
The set of all instructions (in binary form) makes up the
computer's machine language. This is also referred to as
the instruction set.
Machine language instructions usually are made up of
several fields. Each field specifies different information
for the computer. The major two fields are:
Opcode field which stands for operation code and it
specifies the particular operation that is to be performed.
Each operation has its unique opcode.
Operands fields which specify where to get the source
and destination operands for the operation specified by
The source/destination of operands can be a constant, the
memory or one of the general-purpose registers.
Built from two pieces
Add R1, R3, 3
What to do
with the data
get data and
◦ add, sub, mult
◦ and, or
◦ ld, st
Each operand taken from a particular
add r1, r2, r3
add r1, r2, 10
mov r1, (r2)
mov r1, 10(r3)
Reflect processor data pathways
ASCII, American Standard Code for
Information Interchange, is a scheme used for
assigning numeric values to punctuation
marks, spaces, numbers and other
characters. ASCII uses 7 bits to represent
characters. The values 000 0000 through 111
1111 or 00 through 7F are used giving ASCII
the ability to represent 128 different
characters. An extended version of ASCII
assigns characters from 80 through FF.
Accessibility to system hardware
Assembly Language is useful for implementing system software
Also useful for small embedded system applications
Space and Time efficiency
Understanding sources of program inefficiency
Tuning program performance
Writing compact code
Writing assembly programs gives the computer designer the needed
deep understanding of the instruction set and how to design one
To be able to write compilers for HLLs, we need to be expert with
the machine language. Assembly programming provides this
Shows how program interfaces with the processor,
operating system, and BIOS.
Shows how data is represented and stored in
memory and on external devices.
Clarifies how processor accesses and executes
instructions and how instructions access and
Clarifies how a program accesses external devices.
1. Assembly Language is used when speed and
reliability are the overriding factor like small
footprint real-time operating systems.
2. By using assembly language, programmers can
maximize on speed to a level. It is easy to write
than machine code programs.
3. It allows the programmer access to registers or
instructions that are not usually provided by a
4. The main Application of Assembly Language is
for direct hardware manipulation i.e. device
5. Assembly language also directly correlates
which machine instructions; the only way to get
closer to the machine is to write in binary or hex