Side-by-side comparison
| Parameter | 8085 | 8086 Microprocessor |
|---|---|---|
| Data Bus Width | 8-bit | 16-bit |
| Address Bus Width | 16-bit — 64 KB addressable | 20-bit — 1 MB addressable |
| Clock Speed | 3 MHz (original), 6 MHz (8085AH) | 5 MHz, 8 MHz, 10 MHz variants |
| Multiplexed Bus | AD7–AD0 multiplexed (lower 8 address + data) | AD15–AD0 multiplexed (lower 16 address + data) |
| Instruction Set | 8-bit instructions, accumulator-based | 16-bit instructions, register-rich (AX, BX, CX, DX + segment registers) |
| Segmented Memory | No — flat 64 KB | Yes — CS, DS, SS, ES segment registers |
| Number of Registers | 7 general purpose (A, B, C, D, E, H, L) | 14 registers including segment, pointer, index registers |
| I/O Addressing | 256 I/O ports | 64K I/O ports |
| Interrupt Handling | 5 hardware interrupts (TRAP, RST 7.5, 6.5, 5.5, INTR) | 256 vectored interrupts via IDT |
| Technology | NMOS, 6500 transistors | HMOS, 29,000 transistors |
| Typical Use | Embedded training, lab kits, simple controllers | Early IBM PC (PC/XT), industrial controllers |
Key differences
The 8085 uses an 8-bit data bus and can address only 64 KB of memory — fine for a dedicated controller but limiting for any general-purpose software. The 8086 doubled the data path to 16 bits and expanded the address bus to 20 bits using segmentation (Physical Address = Segment × 16 + Offset), reaching 1 MB. The 8086 introduced a pre-fetch queue of 6 bytes, overlapping instruction fetch with execution — the embryo of pipelining absent in the 8085. Interrupt handling grew from 5 fixed vectors in the 8085 to 256 fully vectored interrupts in the 8086, making real-time OS design tractable.
When to use 8085
Use the 8085 for educational lab experiments and simple 8-bit embedded controllers where cost and simplicity are paramount. Most engineering lab kits (like the ALS-SDA-8085 trainer) are built around it for this exact reason.
When to use 8086 Microprocessor
Use the 8086 when 16-bit processing, larger memory addressing, or studying the x86 architecture lineage is the requirement. The original IBM PC 5150 used the 8088 (8-bit external bus version of 8086), which is the direct ancestor of every x86 PC processor today.
Recommendation
For university exams and placement prep, choose to discuss the 8086 when asked about architectural advancement — its segmented memory, 16-bit ALU, and prefetch queue are all examinable. Study the 8085 for instruction set questions since most lab programs are written for it.
Exam tip: The single most tested fact in university papers is the physical address calculation for the 8086: PA = (Segment Register × 10H) + Offset Register — practice this with at least three numerical examples.
Interview tip: A placement interviewer at an embedded systems company like Tata Elxsi or HCL expects you to state that the 8086's prefetch queue (6 bytes) was the first step toward pipelining in the x86 family — that historical insight shows deeper understanding than just listing bus widths.