Assembly language
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Assembly language is a low-level programming language designed for specific processor families, allowing programmers to write human-readable instructions that correspond closely to machine language. It provides maximum control over the computer's operations but is not portable and requires explicit detail in programming. Understanding assembly language offers insights into how programs interact with hardware, enables efficient execution, and is essential for time-critical tasks, although it also has limitations like difficulty in maintenance and readability.
Assembly language
- 1. Assembly language What is Assembly Language? Each personal computer has a microprocessor that manages the computer's arithmetical, logical, and control activities. Each family of processors has its own set of instructions for handling various operations such as getting input from keyboard, displaying information on screen and performing various other jobs. These set of instructions are called 'machine language instructions'. A processor understands only machine language instructions, which are strings of 1's and 0's. However, machine language is too obscure and complex for using in software development. So, the low- level assembly language is designed for a specific family of processors that represents various instructions in symbolic code and a more understandable form.
- 2. Assembly language Why is ASM useful? Machine language is just a series of numbers, which is not easy for humans to read. Using ASM, programmers can write human- readable programs that correspond almost exactly to machine language. The disadvantage is that everything the computer does must be described explicitly, in precise detail. The advantage is that the programmer has maximum control over what the computer is doing. Why is ASM a "low-level" language? Assembly is called a low-level programming language because there is (nearly) a one-to-one relationship between what it tells the computer to do, and what the computer does. In general, one line of an assembly program contains a maximum of one instruction for the computer.
- 3. Assembly language How is ASM different from a "high-level" language? High-level languages provide abstractions of low-level operations which allow the programmer to focus more on describing what they want to do, and less on how it should be done. Programming this way is more convenient and makes programs easier to read at the sacrifice of low-level control. Is ASM portable? No. Because assembly languages are tied to one specific computer architecture, they are not portable. A program written in one assembly language would need to be completely rewritten for it to run on another type of machine.
- 4. Assembly language Advantages of Assembly Language Having an understanding of assembly language makes one aware of − How programs interface with OS, processor, and BIOS; How data is represented in memory and other external devices; How the processor accesses and executes instruction; How instructions access and process data; How a program accesses external devices. Other advantages of using assembly language are − It requires less memory and execution time; It allows hardware-specific complex jobs in an easier way; It is suitable for time-critical jobs; It is most suitable for writing interrupt service routines and other memory resident programs.
- 5. Assembly language An assembly language program can be divided into 3 sections:- The data section The bss section The text section The data Section The data section is used for declaring initialized data or constants. This data does not change at runtime. You can declare various constant values, file names, or buffer size, etc., in this section. The syntax for declaring data section is − section.data The bss Section The bss section is used for declaring variables. The syntax for declaring bss section is − section.bss
- 6. Assembly language The text section The text section is used for keeping the actual code. This section must begin with the declaration global _start, which tells the kernel where the program execution begins. The syntax for declaring text section is − section.text global _start _start: how it works: Most computers come with a specified set of very basic instructions that correspond to the basic machine operations that the computer can perform. For example, a "Load" instruction causes the processor to move a string of bits from a location in the processor's memory to a special holding place called a register.
- 7. Assembly language Assuming the processor has at least eight registers, each numbered, the following instruction would move the value (string of bits of a certain length) at memory location 3000 into the holding place called register 8: The programmer can write a program using a sequence of these assembler instructions. This sequence of assembler instructions, known as the source code or source program, is then specified to the assembler program when that program is started. The assembler program takes each program statement in the source program and generates a corresponding bit stream or pattern (a series of 0's and 1's of a given length). L 8,3000
- 8. Assembly language The output of the assembler program is called the object code or object program relative to the input source program. The sequence of 0's and 1's that constitute the object program is sometimes called machine code. The object program can then be run (or executed) whenever desired. Assembler An assembler is a program that takes basic computer instructions and converts them into a pattern of bits that the computer's processor can use to perform its basic operations. Some people call these instructions assembler language and others use the term assembly language.
- 9. Assembly language While assembly languages differ between processor architectures, they often include similar instructions and operators. Below are some examples of instructions supported by x86 processors. • MOV - move data from one location to another • ADD - add two values • SUB - subtract a value from another value • PUSH - push data onto a stack • POP - pop data from a stack • JMP - jump to another location • INT - interrupt a process the following assembly language can be used to add the numbers 3 and 4: mov eax, 3 - loads 3 into the register "eax" mov ebx, 4 - loads 4 into the register "ebx" add eax, ebx, ecx - adds "eax" and "ebx" and stores the result (7) in "ecx"
- 10. Assembly language limitations of assembly language • No Symbolic names for memory locations. You need to keep track of the exact memory location that a piece of data is stored. That is, you must manipulate memory locations directly. • Hard to read. Although we've made a few improvements by eliminating hex code, the command names are not always clear. • Code is still machine dependent. We haven't really moved that far away from the machine language - just put psuedo-English labels on it. We still need to rewrite every piece of code for every machine. • Hard to maintain and debug. Finding mistakes in machine code is difficult. Correcting them or adding new features can also be a challenge. • Code must be heavily documented. It's very difficult (if not impossible) to figure out what a program does by reading the code. Detailed explanation must be prepared for future coders (including the original programmer) who need to modify or use the code.