23.4.1. Horizontal Micro-Program

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.

Micro-programming refers to the method of implementing the control logic of a computer using micro-instructions. Vertical micro-programming optimizes the structure by compressing the signals, whereas horizontal micro-programming is characterized by a flat format without optimization, leading to simpler control memory but potentially larger memory usage.

Think of micro-programming as organizing files in a cabinet. Vertical micro-programming is like neatly stacking various categories of documents in a compact manner, making retrieval efficient. Horizontal micro-programming, on the other hand, resembles spreading out a large amount of paperwork across a wide surface without organization, making it easy to access any document but cluttered.

Now, encoding can be very flat like you if there are 16 bits as output, you go for a 4:16 decoder that is the one way of compressing them there can be several others as we look here. So, basically first the most formal or the preliminary way of doing it is basically encode the signals in the control memory.

Encoding in micro-programming involves translating control signals into a more compact format using decoders. For example, a 4:16 decoder helps compress 4 input lines into 16 output lines, effectively reducing the control memory size needed. This technique allows for simplifying control signal management while conserving memory space.

Imagine you have a series of light switches for a set of bulbs. Instead of having individual switches for each bulb, you can use a single large switch that controls multiple bulbs at once. This is similar to how encoding condenses multiple signals into fewer inputs to manage them efficiently.

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.

The use of a 3:8 decoder means that only 3 bits of memory are needed to control 8 outputs. This compression of memory size exemplifies the efficiency of encoding signals, allowing the micro-program control unit to manage multiple signals with fewer bits. Thus, the control memory gets significantly reduced in size, increasing efficiency.

Consider a remote control for a TV. Instead of needing separate buttons for every channel, there might be a few buttons that switch between groups of channels. This remote with compact grouping is analogous to how a decoder compresses multiple control signals into fewer bits.

But the problem is that at any point of time only one of these signals can be made 1. So now, the things will start becoming slower.

While vertical micro-programming allows for memory reduction, it comes with limitations. At any given time, only one control signal can be activated. This means operations that previously could occur simultaneously in horizontal micro-programming must now be executed in a sequence. As a result, the processing speed may decrease, requiring more time to complete operations.

Imagine a single-lane bridge where cars must take turns to cross. Only one car can use the bridge at a time, leading to delays. Similarly, the constraint of a single active control signal at a time slows down the operation of the system.

Now, we have to give a time step where you reset actually both, in case of a horizontal micro-program you need not worry about resetting it or holding the value.

In vertical micro-programming, after completing an operation and changing a control signal, there is a need to reset that signal before activating another. This requires careful timing management and can contribute to processing delays, while horizontal systems can maintain multiple active signals simultaneously without needing resets.

Consider a car wash with a single wash station. Cars must get washed one at a time and then leave the wash area before the next car can start. This is similar to how vertical micro-programming requires resetting signals before moving to the next step, causing a delay.

But, the advantage is that the memory size actually gets compressed in the value of in the terms of log from 2n, it will go to the order of n.

Even though vertical micro-programming can slow down processing and increase complexity, a significant advantage is the compression of the control memory, allowing the system to manage resources more effectively. It shifts memory requirements from exponential to logarithmic, significantly reducing the amount of memory needed to achieve the same set of control operations.

Think of packing a suitcase. If you can neatly fold your clothes (encoding), you can fit far more items into the same suitcase than if you were merely tossing them in. This efficient packing strategy relates to how vertical micro-programming reduces the memory size needed for control signals.

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.

A hybrid approach involves creating clusters of signals that are frequently activated together. By logically partitioning the control signals into clusters, multiple signals can be activated at the same time without falling into the limitations of sequential operations. This approach combines the benefits of both vertical and horizontal techniques.

It's like organizing books on a shelf into different sections, such as fiction and non-fiction. You can easily access all fiction books simultaneously while still having a dedicated space for non-fiction. This clustering allows parallel access within the sections, similar to how grouped signals can operate simultaneously.

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