8086 vs Other Microprocessors - Detailed Comparison
Understand how the 8086 microprocessor compares with its predecessors and successors. Learn about the evolution of Intel's x86 architecture and competitive processors from other manufacturers.
Evolution of Intel Microprocessors
The 8086 represents a significant milestone in microprocessor evolution, introducing the x86 architecture that dominates personal computing today.
Key Evolutionary Milestones:
- 8008: First 8-bit microprocessor
- 8080: Enhanced 8-bit with better instruction set
- 8085: Integrated clock generator and system controller
- 8086: First 16-bit processor, birth of x86 architecture
- 80286: Added protected mode and memory management
- 80386: Full 32-bit processor with virtual memory
8086 vs 8080/8085 Comparison
Architecture Comparison
Feature 8080 8085 8086
=================================================
Data Bus Width 8-bit 8-bit 16-bit
Address Bus Width 16-bit 16-bit 20-bit
Addressable Memory 64KB 64KB 1MB
Internal Registers 7×8-bit 7×8-bit 14×16-bit
Clock Speed 2-3 MHz 3-5 MHz 5-10 MHz
Instruction Queue None None 6-byte
Segmentation None None Yes
Coprocessor Support None None Yes
Power Supply +5V,+12V,-5V +5V +5V
Package 40-pin 40-pin 40-pin
Register Comparison
8080/8085 Registers:
- Accumulator: A (8-bit)
- General Purpose: B, C, D, E, H, L (8-bit each)
- Stack Pointer: SP (16-bit)
- Program Counter: PC (16-bit)
8086 Registers:
- General Purpose: AX, BX, CX, DX (16-bit, can split to 8-bit)
- Index: SI, DI (16-bit)
- Pointer: SP, BP (16-bit)
- Segment: CS, DS, SS, ES (16-bit)
- Instruction Pointer: IP (16-bit)
- Flags: FLAGS (16-bit)
Advantage: 8086 has more and wider registers
Instruction Set Comparison
8080 Instructions: ~78 instructions
8085 Instructions: ~80 instructions (added RIM, SIM)
8086 Instructions: ~135+ instructions
New instruction categories in 8086:
- String operations (MOVS, CMPS, SCAS, LODS, STOS)
- Multiply/Divide (MUL, IMUL, DIV, IDIV)
- Bit manipulation (TEST, SHL, SHR, ROL, ROR)
- Loop controls (LOOP, LOOPZ, LOOPNZ)
- Procedure calls (CALL, RET with stack management)
8086 vs 80286 Comparison
Technical Specifications
Feature 8086 80286
=====================================
Data Bus 16-bit 16-bit
Address Bus 20-bit 24-bit
Addressable Memory 1MB 16MB
Operating Modes Real Real + Protected
Clock Speed 5-10 MHz 6-25 MHz
Cache None None
MMU None Yes
Multitasking Software Hardware
Backward Compatibility N/A 100% with 8086
Performance Baseline 3-5x faster
Protected Mode Features
The 80286 introduced protected mode, which 8086 lacks:
- Memory Protection: Prevents programs from accessing unauthorized memory
- Virtual Memory: Supports memory swapping and larger address spaces
- Privilege Levels: Four privilege levels for system security
- Multitasking: Hardware support for task switching
- Larger Memory: 16MB vs 1MB addressable memory
Performance Improvements
Instruction Execution (average cycles):
Instruction Type 8086 80286 Improvement
================================================
Register-Register 2-4 2 1-2x faster
Register-Memory 8-16 5 1.6-3.2x faster
Memory-Memory 16-24 7 2.3-3.4x faster
String Operations 9-17 3 3-5.7x faster
Multiply 70-118 13 5.4-9x faster
Divide 84-190 16 5.3-12x faster
8086 vs 80386 Comparison
Architecture Evolution
Feature 8086 80386
=====================================
Architecture 16-bit 32-bit
Data Bus 16-bit 32-bit
Address Bus 20-bit 32-bit
Addressable Memory 1MB 4GB
General Registers 8×16-bit 8×32-bit
Segment Registers 4×16-bit 6×16-bit
Operating Modes Real Real+Protected+Virtual
Cache None Optional
Paging None Yes
Virtual 8086 Mode None Yes
Register Extension
8086 Registers → 80386 Extended Registers:
AX → EAX (32-bit) BX → EBX (32-bit)
CX → ECX (32-bit) DX → EDX (32-bit)
SI → ESI (32-bit) DI → EDI (32-bit)
SP → ESP (32-bit) BP → EBP (32-bit)
New segment registers in 80386:
FS, GS (additional data segments)
Backward Compatibility:
- AX still accesses lower 16 bits of EAX
- AH, AL still access high/low bytes
- All 8086 instructions work unchanged
Memory Management Comparison
8086 vs Competitive Processors
Motorola 68000 vs 8086
Feature 8086 68000
=====================================
Introduction Year 1978 1979
Data Bus 16-bit 16-bit
Address Bus 20-bit 23-bit
Addressable Memory 1MB 8MB
Internal Architecture 16-bit 32-bit
General Registers 8×16-bit 8×32-bit + 8×32-bit
Addressing Modes 7 14
Clock Speed 5-10 MHz 8-16 MHz
Instruction Set CISC CISC
Package 40-pin 64-pin
Zilog Z8000 vs 8086
Feature 8086 Z8000
=====================================
Introduction Year 1978 1979
Architecture 16-bit 16-bit
Address Bus 20-bit 20-bit
Addressable Memory 1MB 1MB (segmented)
8MB (non-segmented)
General Registers 8×16-bit 16×16-bit
Addressing Modes 7 8
Clock Speed 5-10 MHz 6-10 MHz
Market Success Dominant Limited
Market Impact Comparison
- 8086/8088: IBM PC adoption led to x86 dominance
- 68000: Used in Apple Macintosh, Amiga, Atari ST
- Z8000: Limited adoption, mainly embedded systems
- Success Factors: IBM partnership, software compatibility, price
Performance Benchmarks and Analysis
Numerical Performance Comparison
Problem: Calculate performance for matrix multiplication (3×3) on different processors.
Matrix Multiplication Performance (3×3 matrices):
8080 @ 3 MHz:
- No hardware multiply
- Each multiply: ~50 software multiply cycles
- Total: ~1350 cycles for 27 multiplications
- Time: 1350 × (1/3MHz) = 450 μs
8086 @ 8 MHz:
- Hardware multiply instruction
- Each multiply: ~75 cycles (including setup)
- Total: ~2025 cycles for 27 multiplications
- Time: 2025 × (1/8MHz) = 253 μs
80286 @ 12 MHz:
- Optimized multiply: ~13 cycles
- Total: ~351 cycles for 27 multiplications
- Time: 351 × (1/12MHz) = 29.25 μs
Performance Improvement:
8086 vs 8080: 450/253 = 1.78× faster
80286 vs 8086: 253/29.25 = 8.65× faster
80286 vs 8080: 450/29.25 = 15.4× faster
Memory Access Speed Comparison
Memory Read Operation (1000 consecutive reads):
8085 @ 5 MHz:
- Memory read: 3 T-states = 3 × 200ns = 600ns per read
- Total time: 1000 × 600ns = 600 μs
8086 @ 8 MHz:
- Memory read: 4 T-states = 4 × 125ns = 500ns per read
- Total time: 1000 × 500ns = 500 μs
With prefetch queue optimization:
- Many instructions already in queue
- Effective time: ~400 μs
Improvement: 600/400 = 1.5× faster for sequential access
Code Efficiency Analysis
String Copy Operation (100 bytes):
8080 Assembly:
LXI H, SOURCE ; 3 bytes
LXI D, DEST ; 3 bytes
MVI B, 100 ; 2 bytes
LOOP:
MOV A, M ; 1 byte, 7 cycles
STAX D ; 1 byte, 7 cycles
INX H ; 1 byte, 5 cycles
INX D ; 1 byte, 5 cycles
DCR B ; 1 byte, 5 cycles
JNZ LOOP ; 3 bytes, 10 cycles
Total: 16 bytes, 39 cycles × 100 = 3900 cycles
8086 Assembly:
MOV SI, SOURCE ; 3 bytes
MOV DI, DEST ; 3 bytes
MOV CX, 100 ; 3 bytes
REP MOVSB ; 2 bytes, 9+17×100 cycles
Total: 11 bytes, 1709 cycles
Improvement:
- Code size: 16/11 = 1.45× smaller
- Execution: 3900/1709 = 2.28× faster
Application Domain Comparison
Processor Application Matrix
Application Domain 8080/8085 8086 80286 80386
=======================================================
Embedded Systems Excellent Good Limited Limited
Personal Computers Limited Excellent Good Excellent
Workstations Poor Limited Good Excellent
Servers Poor Poor Limited Good
Real-time Systems Good Good Good Good
Gaming Systems Limited Good Good Excellent
Industrial Control Excellent Good Limited Limited
Software Ecosystem
Market Success Factors
- IBM PC Adoption: 8088 (8086 variant) chosen for IBM PC
- Software Compatibility: Easy migration from 8080 software
- Third-party Support: Multiple vendors, competitive pricing
- Development Tools: Comprehensive software development ecosystem
- Backward Compatibility: Smooth upgrade path to newer processors
Cost-Performance Analysis
Historical Pricing (1980s)
Processor Pricing Comparison (approximate 1982 prices):
Processor Price Performance* Cost/Performance
========================================================
8080 $15 1.0 $15.00
8085 $20 1.2 $16.67
8086-4 $360 3.5 $102.86
8086-8 $500 5.0 $100.00
8088-5 $150 2.8 $53.57
80286-6 $450 12.0 $37.50
*Performance relative to 8080 baseline
Cost-effectiveness ranking:
1. 8080 (baseline)
2. 8085 (slight premium for integration)
3. 8088 (best 16-bit cost/performance)
4. 8086 (premium for full 16-bit bus)
5. 80286 (best absolute performance)
System Cost Comparison
Complete System Cost (1982):
8080-based System:
- CPU: $15
- Memory (16KB): $200
- I/O chips: $100
- Total: ~$315
8086-based System:
- CPU: $500
- Memory (64KB): $400
- I/O chips: $150
- Total: ~$1050
Price premium: 1050/315 = 3.33×
Performance gain: ~5×
Value proposition: Better performance per dollar
Architectural Limitations and Strengths
8086 Limitations
- Segmented Memory: Complex addressing, 64KB segment limit
- No Memory Protection: Programs can crash system
- No Multitasking Support: Cooperative multitasking only
- Limited Address Space: 1MB maximum
- No Cache: All memory accesses go to external memory
8086 Strengths
- 16-bit Operations: Efficient word processing
- Rich Instruction Set: Powerful string and arithmetic operations
- Hardware Multiply/Divide: Fast mathematical operations
- Flexible Addressing: Multiple addressing modes
- Coprocessor Support: 8087 FPU integration
- Backward Compatibility: Easy 8080 code migration
Design Philosophy Comparison
Legacy and Impact
Long-term Influence
- x86 Architecture: Foundation for all modern Intel/AMD processors
- Software Compatibility: DOS programs still run on modern systems
- Industry Standards: Established PC architecture conventions
- Market Dominance: Led to Intel's market leadership
Modern Relevance
8086 Features in Modern Processors:
Feature 8086 Modern x86-64
==========================================
Basic instruction set ✓ ✓ (extended)
Segmentation ✓ ✓ (legacy mode)
Real mode ✓ ✓ (compatibility)
Register organization ✓ ✓ (extended to 64-bit)
Little-endian byte order ✓ ✓
CISC instruction set ✓ ✓ (RISC µops internally)
Evolutionary path:
8086 → 80286 → 80386 → 80486 → Pentium → ... → Core → Ryzen
Educational Value
The 8086 remains important for education because it:
- Demonstrates fundamental microprocessor concepts
- Has manageable complexity for learning
- Shows evolution of computer architecture
- Provides foundation for understanding modern processors
- Illustrates trade-offs in processor design
Summary
The 8086 microprocessor represents a pivotal moment in computing history. While it had limitations compared to some contemporary designs like the 68000, its combination of performance, IBM PC adoption, and backward compatibility made it the foundation of the most successful processor architecture in history. Understanding how 8086 compares to other processors provides valuable insights into processor design trade-offs and market dynamics.
Key Takeaways:
- 8086 introduced 16-bit processing and x86 architecture
- Significant performance improvement over 8-bit predecessors
- Market success due to IBM PC adoption and software ecosystem
- Architectural decisions influenced decades of processor development
- Balance of performance, compatibility, and cost was key to success
- Legacy continues in modern x86-64 processors
