60 8086 microprocessor viva questions and answers for Sunday-evening exam prep, covering architecture, addressing modes, arithmetic and flags, the stack, interrupts and DOS/BIOS calls, each answer linked to a worked program or reference post.
Complete 8086 addressing modes reference: all 9 modes with EA formulas, default segment rules, clock-cycle costs, the [BX+SI] vs [BX+DI] timing asymmetry, and all five string instructions (MOVS, CMPS, SCAS, LODS, STOS) with REP/REPE/REPNE, auto-adjustment table, and worked examples.
All 9 flags of the 8086 flag register explained: CF, PF, AF, ZF, SF, OF (status) and TF, IF, DF (control) with exact set/clear conditions, the CF vs OF unsigned/signed distinction, the four traps that catch every beginner, and a complete conditional jump reference.
The complete 8086 stack reference: SS:SP model, byte-level PUSH/POP mechanics, near and far CALL/RET, stack frame setup with BP for parameters and locals, and the INT/IRET stack protocol.
The 8086 interrupt system: IVT layout at 00000h-003FFh, the six-step hardware acknowledgment sequence, writing correct ISRs with register save/restore/EOI/IRET, vector installation via DOS INT 21h, and a complete worked timer ISR example.
How the Intel 8086 splits work between the Bus Interface Unit (BIU) and Execution Unit (EU) to create a two-stage pipeline, with the complete 40-pin signal reference (minimum and maximum mode), T-state bus cycle timing, even/odd memory banks, and the full I/O subsystem including 8255 PPI, 8259 PIC, and 8253 timer.
A complete 8086 assembly program implementing the Sieve of Eratosthenes to find all prime numbers up to 50. Includes annotated source code, algorithm walkthrough, how-the-code-works breakdown, sample output, and a common-mistakes table.
A fully working 8086 assembly language calculator that performs addition, subtraction, multiplication, and division on 16-bit numbers. Includes annotated source code, algorithm walkthrough, sample output, and a common-mistakes table.
A complete guide to handling the 8086 external timer interrupt INT 08h. Covers the interrupt vector table, how the CPU dispatches interrupts, saving and restoring the original BIOS handler, writing a far ISR that increments a tick counter, chains correctly, and exits safely — with a common-mistakes table.
A complete guide to 8086 assembly stack operations. Covers how the stack works (SP, SS, LIFO), what PUSH and POP do to memory, how CALL saves a return address and RET retrieves it, and a fully annotated working program that demonstrates all four instructions together.