Horizontal & Vertical Microprogramming | Computer Architecture & Organisation (CAO) - Computer Science Engineering (CSE) PDF Download

Introduction

• In the Horizontal micro-programmed control unit, the control signals are represented in the decoded binary format, i.e., 1 bit/CS. Here ‘n’ control signals require n bit encoding. On the other hand. 
• In a Vertical micro-programmed control unit, the control signals are represented in the encoded binary format. Here ‘n’ control signals require log2n bit encoding. 

Difference between Horizontal and Vertical micro-programmed Control Unit:

Example: Consider a hypothetical Control Unit that supports 4 k words. The Hardware contains 64 control signals and 16 Flags. What is the size of control word used in bits and control memory in a byte using: 
(a) Horizontal Programming 
(b) Vertical programming

(a) For Horizontal 
64 bits for 64 signals % 16 bits for flags
Control Word Size = 64 + 16 = 80 bits
Control Memory = 4 kW = ( (4* 80) / 8 ) = 40 kByte

(b) For Vertical
6 bits for 64 signals i.e log264
4 bits for 16 flags i.e log216
12 bits for 4K words i.e log2(4*1024)
Control Word Size = 4 + 6 + 12 = 22 bits
Control Memory = 4 kW = ( (4* 22) / 8 ) = 11 kByte