Introduction: What this topic is and why it matters
A microprocessor is the central processing unit (CPU) of a computer fabricated on a single integrated-circuit (IC) chip. It fetches instructions from memory, decodes them, and executes them — performing arithmetic, logic, data movement, and control operations. The Intel 8085 (an 8-bit processor, 1976) and the Intel 8086 (a 16-bit processor, 1978) are the two chips that Bangladeshi competitive exams (BCS, Bank IT/AsstProgrammer, IT-officer, teacher recruitment) return to again and again, because they are the classic teaching processors of every university syllabus.
Exam questions on this topic are highly predictable and factual: "How many address lines does the 8085 have?", "What is the physical address for CS = 2000H, IP = 0034H?", "After RESET the 8086 starts at which address?", "Difference between microprocessor and microcontroller / RISC and CISC?", "Name the addressing modes." This lesson closes the entire Microprocessor subject so you can answer every such question with confidence.
Source: Intel 8085 launched March 1976; Intel 8086 launched 8 June 1978; Intel 8051 microcontroller introduced 1980 (Intel history timeline; Wikipedia: Intel 8085, Intel 8086, Intel MCS-51).
Learning objectives
- Distinguish a microprocessor from a microcontroller and state where each is used.
- Describe the 8085 architecture: registers, ALU, flags, address/data buses, and key pins.
- Describe the 8086 architecture: BIU and EU, the four segment registers, and the 20-bit address bus giving 1 MB memory.
- Compute a physical address from a segment and offset, and explain the RESET → FFFF0H behaviour.
- Compare RISC vs CISC.
- Identify the five addressing modes with examples.
- Read and hand-assemble common instructions: MOV, ADD, ADC, SUB, XCHG, PUSH, POP, JNZ, JMP.
- Outline the 8255 PPI control word and the 8051 microcontroller for embedded use.