23.4. Comparison of Micro-Program Approaches

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.

In vertical micro-programming, the focus is on optimizing the way control signals are stored in memory. Instead of having a flat structure (as seen in horizontal micro-programming) where all signals are available at once, vertical micro-programming encodes these signals compactly. This allows for smaller memory usage because fewer bits are needed to represent the necessary control signals.

Think of vertical micro-programming like a zip file on your computer that compresses several files into one. This makes it take up less space while still allowing you to access the essential contents when needed. Similar to how you unpack a zip file, the system needs to decode the control signals when they are needed, but you save storage space overall.

So, the most formal or the preliminary way of doing it is basically encode the signals in the control memory. So, whatever signals has to be applied you just encode them and use a decoder.

When we encode signals in control memory, we store them in a compressed format. This means that each signal is represented by fewer bits than it normally would be. A decoder is then used to convert these compacted signals back into their original form when needed. For instance, if you have 8 bits that control different functions, using a decoder allows you to represent these functions with fewer bits, thereby optimizing memory use.

Imagine encoding a long message into a short code so that it takes up less space. When you want to read or send this message, a decoder translates the code back into the original message. This is how control signals are handled in micro-programming—keeping them efficient while still being readable or actionable when required.

So, here we are compressing it we are calling as a vertical micro-program because we are compressing the structure of the memory. So, you can only make any one point one at a time. So I make 𝑃𝐶 = 1 and at a time 1, then in the next time I make 𝑀𝐴𝑅 = 1.

In vertical micro-programming, you can only activate one control signal at a time due to the compressed nature of the setup. For example, if you need to set the Program Counter (PC) high first, you must do that before setting the Memory Address Register (MAR) high. This sequential operation can lead to a longer time to execute tasks because multiple control signals cannot be activated simultaneously.

Consider a small elevator that can only carry one person at a time. If two people want to go to different floors, the first person must exit before the next one can board. This limitation means it takes longer to transport all individuals compared to an elevator that can carry multiple people at once.

The disadvantage is that you have to you can you will have more number of steps required to give simultaneous 1s to the different control positions.

One major drawback of vertical micro-programming is the increased time taken to execute instructions. Since only one control signal can be activated at a time, the system requires more steps to accomplish what could potentially be done in fewer steps in a horizontal approach where multiple signals can be activated simultaneously. This results in slower performance, although memory usage remains efficient.

Think of a person trying to perform several tasks by themselves, like cooking, cleaning, and setting the table. If they can only focus on one task at a time, it will take longer to finish everything compared to having several people doing each task at once.

Another way is very interesting that can I make a cluster? So, what is the cluster idea I will take a figure and then I will come back to the theory.

The hybrid approach introduces clusters, which allow certain control signals to be activated simultaneously within different groups. By organizing the signals into clusters, like PC and MAR, that do not need to be activated at the same time, the system can take advantage of some parallelism while still maintaining a level of compression.

Think of a team working on a project where some team members tackle different tasks at the same time. For instance, the writing group can be brainstorming while the design group works on visuals. By clustering people into separate tasks, they can complete a project faster than if one person was responsible for every aspect one after another.

In horizontal micro-program less number of micro instructions are required. It’s a fully parallel architecture no encodings, extremely fast, but actually wide control field is required.

A direct comparison shows that horizontal micro-programming is faster and requires fewer micro-instructions since it allows for parallel execution. However, it typically consumes more memory as it requires more bits to represent control signals without compression. This leads to potential wastage due to unused control fields. In contrast, vertical micro-programming saves memory but is slower and needs more steps due to sequential processing.

This can be likened to a factory assembly line. A wide assembly line (horizontal) can produce many products simultaneously, but it requires more space and resources. In contrast, a narrow line (vertical) allows for less resource consumption but processes items one at a time, slowing down production.

--