Pentium Microprocessor Overview

The Pentium Microprocessor

• Significance: The Pentium microprocessor was a significant advancement in computer technology, known for its performance and features.

• Author: The book "The Pentium Microprocessor" was authored by Intel Corporation.

• Publisher: Intel Corporation also published the book.

• Publication Year: The book was published in 1993.

• Trademark: The trademark associated with the Pentium microprocessor is Pentium.

• Cataloging Section: The cataloging section contains information about the book's publication details, ISBN, and Library of Congress Control Number.

• Content: It covers the architecture, instruction set, programming, and applications of the Pentium microprocessor.

• Editorial Supervision: Intel Corporation was responsible for the editorial supervision of the book.

Pentium Registers and Flags

• Carry Flag (CF): Indicates whether an arithmetic operation resulted in a carry or borrow out of the most significant bit.

• Zero Flag (ZF): Indicates if the result of an arithmetic or logical operation is zero.

• Overflow Flag (OF): Indicates if an arithmetic operation resulted in an overflow (a result exceeding the capacity of the register).

• Interrupt Flag (IF): Determines if the processor is enabled or disabled to handle hardware interrupts.

Pentium Data Representation and Directives

• Byte: A byte in the Pentium architecture is equivalent to 8 bits.

• 16-bit Numbers: 16-bit numbers are represented using two bytes.

• Auxiliary Flag (AF): Indicates if there was a carry or borrow from the lower half of a byte to the upper half.

• Data Flag (DF): Determines the direction of string operations (forward or backward).

• DB Directive: Stands for "Define Byte." Used to define data as 1-byte values in assembly language.

• Byte-Swapping: In Intel data organization, low-order bytes come first, and high-order bytes come later. This requires swapping bytes when exchanging data with systems using a different byte order.

• DB and DW Directives: DB is used for 1-byte data, while DW is used for 2-byte (word) data.

• MSG Data Definition: The data definition for MSG in the sample occupies 7 bytes.

• EQU Directive: Equates a symbol to a constant value.

• 7 DUP(?) : Defines an array containing 7 elements, with each element initialized to undefined values.

• 1234H: Represents the hexadecimal value 1234 in the DW directive.

• p Notation: 'p' signifies a pointer.

80286 Memory Management

• Address Unit: In the 80286 processor, the address unit is 16 bits.

• Virtual Memory: Allows programs larger than physical memory to execute by swapping portions of the program between memory and disk.

• Protected Virtual Address Mode: Provides advantages over 8086 real address mode, including memory protection, multitasking, and virtual address space.

• Segment Descriptors: Control the access rights and location of segments in memory.

• Access Rights Byte: Determines who can access a segment (user or system), what type of access is permitted (read, write, execute), and privilege levels.

• Protection Enable Bit: When set in the 80286's status word, enables the protection mechanisms of the processor.

• 1 Gigabyte Virtual Address Space: Provides a larger address space for programs, enabling the execution of larger programs.

• 8086 Real Address Mode: Used when protected mode is not enabled or when the processor is in real address mode.

8087 Coprocessor

• Purpose: The 8087 coprocessor is primarily used for floating-point arithmetic operations.

80386 and 80486 Processors

• 80486 vs. 80386: The 80486 offers significantly higher performance compared to the 80386, primarily due to its built-in cache memory.

• Cache Memory: Provides faster access to frequently used data, reducing memory access time.

• Cache Hit: When data is found in the cache, it's called a cache hit. This reduces the latency of memory access, improving performance.

• Average Memory Access Time: The average time taken to access data considering cache hits and misses.

• Hit Ratio of 0.85: If the hit ratio is 0.85, it means 85% of memory accesses are cache hits, contributing to faster performance.

• 80486 Features: In addition to the cache memory, the 80486 features a built-in floating-point unit, instruction prefetching, and branch prediction.

• Cache Miss: If the data is not found in the cache, it results in a cache miss, which means the processor has to fetch data from the slower main memory.

• Addressing Space: The 80486 has a 32-bit addressing space, allowing access to a larger amount of memory compared to the 80386.

Assembly Language Programming

• ORG Command: Sets the origin for the program's code.

• Hexadecimal vs. Decimal: It's essential to distinguish between hexadecimal and decimal numbers in assembly language to avoid errors.

• MOV Instruction: Moves data from a source to a destination.

• ADD Instruction: Adds two operands' values, storing the sum in the destination register.

• INC Instruction: Increments the value of a register or memory location by 1.

• DEC Instruction: Decrements the value of a register or memory location by 1.

• JNZ Instruction: Jumps to another instruction if the Zero Flag (ZF) is not set (i.e., the result of the last operation was not zero).

• RET Instruction: Returns execution to the calling program.