水平和垂直微程序控制单元之间的区别

前提条件–有线v / s微程序控制单元
基本上，控制单元(CU)是在适当顺序的控制信号的帮助下运行计算机所有功能的引擎。在微程序控制单元方法中，与操作相关的控制信号存储在特殊的存储单元中。将导致特定的微操作发生的控制信号集视为“微指令”是很方便的。微指令序列可以存储在内部“控制”存储器中。

根据存储在控制存储器中的控制字的类型，可以将微程序控制单元分为两种类型，即，水平微程序控制单元和垂直微程序控制单元。

• 在水平微程序控制单元中，控制信号以解码的二进制格式表示，即1位/ CS。在此，“ n”个控制信号需要n位编码。另一方面。
• 在垂直微程序控制单元中，控制信号以编码的二进制格式表示。在此，“ n”个控制信号需要log ₂ n位编码。

水平微程序控制单元和垂直微程序控制单元之间的比较：

Horizontal µ-programmed CU	Vertical µ-programmed CU
It supports longer control word.	It supports shorter control word.
It allows higher degree of parallelism. If degree is n, then n Control Signals are enabled at a time.	It allows low degree of parallelism i.e., degree of parallelism is either 0 or 1.
No additional hardware is required.	Additional hardware in the form of decoders are required to generate control signals.
It is faster than Vertical micro-programmed control unit.	it is slower than Horizontal micro-programmed control unit.
It is less flexible than Vertical micro-programmed control unit.	It is more flexible than Horizontal micro-programmed control unit.
Horizontal micro-programmed control unit uses horizontal microinstruction, where every bit in the control field attaches to a control line.	Vertical micro-programmed control unit uses vertical microinstruction, where a code is used for each action to be performedand thedecoder translates this code into individual control signals.
Horizontal micro-programmed control unit makes less use of ROM encoding than vertical micro-programmed control unit.	Vertical micro-programmed control unit makes more use of ROM encoding to reduce the length of the control word.

示例：考虑一个支持4 k个字的假想控制单元。硬件包含64个控制信号和16个标志。使用以下命令以位为单位的控制字和以字节为单位的控制存储器的大小是多少：
a)水平编程
b)垂直编程

解决方案：

a)For Horizontal 

64 bits for 64 signals
Control Word Size = 4 + 64 + 12 = 80 bits

Control Memory = 4 kW = ( (4* 80) / 8 ) = 40 kByte


a)For Vertical
6 bits for 64 signals i.e log264

Control Word Size = 4 + 6 + 12 = 22 bits

Control Memory = 4 kW = ( (4* 22) / 8 ) = 11 kByte