25.3. Vertical Micro Program

So, this is just again very quickly very quickly let us look at now we are going to take a more elaborate depth with more clear examples that, optimization is done on the signals by encoding. So, last unit we have already discussed that encoding is very important.

The speaker is emphasizing the importance of optimizing signals in computers through a process called encoding. Encoding helps to represent the control signals in a more efficient way, improving the overall performance of the CPU.

Think of encoding as translating a long-winded speech into a concise summary. Just like a summary captures the essence without unnecessary details, encoding optimizes control signals to minimize space and enhance processing speed.

To do this we have seen that in the last unit, that we have to optimize by encoding the signals, which is actually called the vertical micro instruction. So, if you just go for a very flat compression that is from 2n, we just compress it to n or from n to log n and using n to 2n decoder, then actually full compression is there.

In microprogramming, there are two types: horizontal and vertical. Horizontal microprograms allow all control signals to be activated simultaneously, but require a lot of memory. In contrast, vertical microprograms use encoding to compress the signal representation, making it much more memory-efficient. This enables the compression of data from 2n bits down to n or even log n bits.

Imagine packing your wardrobe. A horizontal approach means you keep everything hanging, which takes a lot of space. A vertical approach, however, is like folding your clothes neatly into boxes, condensing what you have into a much smaller area. Both ways keep your clothes but vertical packing is much more efficient.

But in this case only one bit signal can be made a 1. So, if simultaneously 3 or 4 points to be a 1 you require 4 cycles for that. But we have seen that this is not a very very good way of solving the problem, because it makes the memory very small, but it will take very long time to solve the problem.

Using full compression in vertical micro programming complicates execution since only one signal can be active at a time. This limitation requires multiple cycles for operations that could potentially be done simultaneously, leading to inefficiency even though memory usage is minimized.

Consider a crowded lift that can carry only one person at a time. Even if there are many individuals wanting to go to different floors, the lift can only go one at a time. This is efficient in terms of space but incredibly slow for those waiting to go up.

So, what we basically do is that, we go for basically something called a hybrid approach in hybrid we make clustering and for each clustering we will try to put signals in one cluster, which need not be 1 simultaneously.

To overcome the limitations of strict vertical microprograms, a hybrid approach is introduced. This involves clustering signals together so that groups of signals that don’t need to be high at the same time can be controlled more effectively, enabling better efficiency and performance.

Think of this as organizing your daily schedule. Instead of trying to fit all activities into a strict timeframe that overlaps, you group similar tasks together, like running errands, to streamline your day and use time wisely.

So, this slide tells about the horizontal micro program that it is one extreme, and it is basically it is longer and in the vertical micro program it is highly compressed. So, it is the other extreme.

In the discussion, the speaker illustrates both ends of the spectrum: the horizontal micro program being slower and requiring more memory, while the vertical micro program is fast but inefficient. The hybrid approach attempts to bring the best of both worlds by optimizing memory usage while maintaining decent processing speeds.

Consider a restaurant menu. A horizontal menu has an extensive list where each dish is described in detail, while a vertical menu has minimal descriptions, making it easy to read but lacking information. A hybrid menu gives you brief descriptions but also categorizes the dishes effectively, making it both efficient and informative.

So, we are taking a single bus architecture, now we will mainly focusing on example because theory mainly we have covered in the last unit. So, if you look at it, this is a single word single bus architecture.

Here, the speaker introduces a specific architecture called the single bus architecture, which will be the focus of the example. This architecture uses one bus to connect multiple components, allowing data to travel between registers and the CPU efficiently.

Imagine a single lane road where cars share the same path to travel. While this can be efficient when traffic is light, it can lead to congestion during peak hours, similar to how a single bus architecture can slow down data transfer as multiple components compete for the same pathway.

So, how many registers total? 1, 2, 3, 4, 5, 6, 7 and for each register you have a input and output port. So, it is 7 into 2 14 signals are there just keep it in mind, then we have a instruction register.

The speaker proceeds to count and detail the number of control signals needed in the single bus architecture. Each register has both input and output ports, contributing to the total signal count required for operation.

Think of a multi-story building where every room has a door for entrance and exit. Just as each door corresponds to an entry or exit point that needs to be counted for safety, each register’s input and output needs to be factored into the total system design for successful communication.

So, let us see what is the count. So, we will see the count in the next slide, but if you take all the counts and put in the flat architecture the size will be very high already we have discussed so many times, which will be a horizontal micro program.

This portion discusses the challenges faced when managing the complexity of signal counts in a flat architecture. A large number of signals lead to an increase in complexity and resource usage, making the horizontal approach less favorable.

Picture trying to manage a large party with no organization. Each person wants to tell their story at the same time, making it chaotic and overwhelming. If you group guests by topics and allow them to share sequentially, the overall experience becomes much better organized.

--