Assembly Language and Computer Structure

Assembly Language and Computer Structure

• Assembly language is a low-level programming language that requires knowledge of computer structure to understand.
• The simple computer model consists of a system bus, CPU, and RAM, where the CPU is the heart of the computer and performs most computations.

General Purpose Registers

• The 8086 CPU has 8 general purpose registers, each with its own name and 16-bit size.
• The registers are: AX, BX, CX, DX, SI, DI, BP, and SP.
• Despite their names, the programmer determines the usage for each register.
• The main purpose of a register is to keep a number (variable).
• 4 general purpose registers (AX, BX, CX, DX) are made of two separate 8-bit registers (e.g., AH and AL).
• Modifying an 8-bit register updates the corresponding 16-bit register, and vice-versa.
• Registers are faster than memory because they are located inside the CPU and do not require the use of a system bus.

Segment Registers

• The segment registers are: CS, DS, ES, and SS.
• CS points to the segment containing the current program.
• DS generally points to the segment where variables are defined.
• ES is an extra segment register, and its usage is defined by the coder.
• SS points to the segment containing the stack.
• Segment registers work together with general purpose registers to access any memory value.
• The CPU calculates the physical address by multiplying the segment register by 10h and adding the general purpose register to it.

Effective Address and Special Purpose Registers

• The address formed with 2 registers is called an effective address.
• By default, BX, SI, and DI registers work with the DS segment register, and BP and SP work with the SS segment register.
• Other general purpose registers cannot form an effective address.
• IP (instruction pointer) and flags register are special purpose registers.
• IP register always works together with the CS segment register and points to the currently executing instruction.
• Flags register is modified automatically by the CPU after mathematical operations and determines the type of the result.

This quiz covers the basics of assembly language, a low-level programming language, and its relation to computer structure, including the CPU, RAM, and system bus.