Fundamentals of Computer Architecture and the 8086 Microprocessor

Core Computer System Components

Hardware, Software, and Firmware Defined

Hardware is the physical part of a system. Software is a set of programs and applications consisting of instructions and routines that are used to coordinate programs and microprogrammable devices. Firmware is system software recorded in the electronic structure of a system, containing a set of programs that serve as intermediaries between software and hardware.

The Arithmetic Logic Unit (ALU)

The ALU (Arithmetic Logic Unit) is the operational part of a microprocessor. This complex combinational circuit is responsible for performing arithmetic and logic operations. ALU types include 0-address, 1-address, 2-address, and 3-address ALUs. Inside the ALU are two registers: the accumulator and the status register.

Key Elements of a Motherboard

A motherboard typically includes:

• A socket for microprocessor installation
• Expansion slots
• A keyboard controller
• A series of connectors (banks)
• A group of IC sockets for cache memory
• A keyboard connector
• A small memory chip called BIOS ROM
• A set of jumpers

The 8086 Microprocessor Architecture

Execution Unit (EU)

The EU (Execution Unit) performs data processing within the 8086 microprocessor. It is responsible for interpreting and executing instructions. The memory range it handles is 64 Kbytes, and its internal buses are 16 bits. It consists of the following elements: the ALU, a 16-bit status register, and eight 16-bit registers (including SP, BP, SI, DI).

Bus Interface Unit (BIU)

The BIU (Bus Interface Unit) is responsible for generating 20-bit physical addresses and ensures that the bus is used at full processing capacity. The BIU pre-fetches instructions and data for storage and reading before they are needed by the EU, storing them in the instruction queue. This leaves the EU free to concentrate on data processing and instruction execution. It is composed of: segment registers (code segment, data segment, stack segment, extra segment), the Instruction Pointer (IP), the instruction queue, and an ALU.

8086 Microprocessor Operating Modes

• Maximum Mode: When working with other microprocessors and buses.
• Minimum Mode: The microprocessor works only with auxiliary chips from its family.

Integrated Circuit Encapsulation Types

Common encapsulation types include:

• Dual In-line Package (DIP)
• Plastic Leaded Chip Carrier (PLCC)
• Leadless Ceramic Chip Carrier (LCCC)
• Pin Grid Array (PGA)
• Single Edge Connector (SEC)

Understanding RAM Types

Dynamic RAM (DRAM)

Dynamic RAM (DRAM) utilizes a property of MOS transistors as the basis for information storage. These transistors form a small capacitor, which is used to store data. When the capacitor is charged, it represents a '1'; when discharged, it represents a '0'. These capacitors tend to discharge, so maintaining data requires periodic refreshing. This is achieved by auxiliary circuitry called refresh circuits.

Static RAM (SRAM)

Static RAM (SRAM) uses flip-flops as its basic storage cell, each capable of storing one bit. SRAM operates very simply; it remains indefinitely in a set or reset state as long as power is supplied and its state is not forced to change. SRAM technology includes bipolar and MOS technologies.