23.1.1. Encoding and Compression

So, whenever we want to optimize based on encoding or compressing of the signals in each of these cells or each of the words in the program control memory, we call it as a vertical micro-program. In horizontal it is very flat and no optimization is there. So now, what way you can do the only way you can do is you have to encode encoded by mean many way xyz.

Vertical micro-programming refers to a method of organizing and optimizing control signals in memory. Unlike horizontal approaches, which are simpler and without optimizations, vertical methods aim to encode these signals for better efficiency. This means arranging the data in a way that reduces the space needed to store it. Essentially, vertical micro-programming focuses on compressing the signals to make the system more efficient.

Imagine organizing a closet. A horizontal approach would be just hanging clothes anywhere, making it messy. In contrast, a vertical method would be like folding your clothes and organizing them by type (shirts, pants, etc.), allowing you to find what you need quickly and taking less space.

So, basically first the most formal or the preliminary way of doing it is basically encode the signals in the control memory. So, what do you do? So, whatever signals has to be applied you just encode them and use a decoder, I will show you a figure and then we will come back.

The encoding of control signals involves translating the signals into a compressed format that can be stored in memory. This is done using a decoder that retrieves and decodes the signals as needed. This preliminary step is crucial as it lays the groundwork for efficient communication between different parts of the computer system, ensuring that the right commands are executed.

Think of this process as writing a grocery list with abbreviations. Instead of writing 'apples' and 'bananas', you might write 'A' and 'B'. When you get to the store, you decode the list in your mind to remember what each letter stands for, making it easier to refer to your list without clutter.

So, how many are there? There are 8 bits which has to be controlled or 8 locations which has to control. So, I just put a 3:8 decoder then, what will be the memory size? The memory size will be 3 bits. So, if you give 000 the corresponding row of the decoder will be 1 and you generate 𝑃𝐶 = 1.

In this example, a 3:8 decoder is used to control 8 different signals with just 3 bits of input. This means that you can use three binary inputs (like 000, 001, etc.) to select one of the eight outputs. The decoder is essentially a switchboard that takes the input and routes it to one specific output, allowing for efficient control of the system without using too much memory.

This is similar to a remote control for your TV where pressing a button (input) selects a specific channel (output). With just a few buttons, you can control an entire range of channels efficiently.

So, here there are 2 disadvantages one is that you have to you can you will have more number of steps required to give simultaneous 1s to the different control positions. So here two 1s are required so, you require 2. If multiple 1s are required you have that many number of time steps.

While vertical micro-programming significantly compresses memory usage (from 2^n to n bits), it has disadvantages. The method requires more steps or time to activate multiple signals at once. In scenarios where two signals need to be on simultaneously, the system must execute actions in steps instead of all at once, leading to slower responses.

Consider a vending machine where to get two snacks (say chips and a soda), you first have to select one and then make a second choice. This is slower than if you could choose both in one go, just like how vertical programming takes longer for simultaneous operations.

So, what I do? I actually make a cluster 2 clusters. In 1 cluster I will put the 𝑃𝐶 , in another cluster actually I will put memory address register in. So, in if there are 2 different clusters basically. So, interestingly what is going to happen I can make this one 1 and this one also simultaneously.

To overcome the limitations of vertical micro-programming, clustering is introduced. This involves organizing signals into groups (clusters) where each group has the ability to activate one signal at a time. By doing this, we can achieve more efficient signal activation without the delays imposed by vertical encoding, creating a balance between the speed of horizontal micro-programming and the space-saving of vertical methods.

Imagine using a multi-lane highway instead of a single lane. Each lane (cluster) can manage its own traffic independently, allowing multiple cars (signals) to move simultaneously without delay, which enhances the overall flow of traffic.

So, basically with this we come to the end of this unit. In the next unit basically, we will look in more depth basically the type depending on different type of instructions or macro instruction.

The section closes by summarizing the key ideas discussed and indicating that future learning will build on these foundations. Students will explore how different instruction types affect micro-program execution and gain further insight into the architecture of micro-program control units.

Think of this like learning the basics of cooking. Once you understand how to make simple dishes, you can move on to more complex recipes. Similarly, mastering encoding and compression in micro-programming sets the stage for deeper studies in computer architecture.

--