Answered: Briefly explain repeat prefix

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Briefly explain repeat prefix

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Step 1: Explanation

The REPE prefix repeats an instruction while Zero flag is set.

REPE/REPZ - Repeat Equal/Repeat Zero

Modifies Flags: None

The object code of REPE/REPZ instruction is 1111 001Z = F3 as Z=1.
“REPE” repeats execution of string instructions while CX!= 0 and the Zero Flag is set.
“CX” is decremented once for each repetition.
Zero Flag is tested after each string operation.
The combination of a repeat prefix and a segment override on processors other than the “386” may result in errors if an interrupt occurs before “CX=0”.

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