23.5.2. Executing Instructions

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. So, whenever we want to optimize on sparse values of a matrix there is only one way to do it we have to encode it.

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.

The text introduces the concept of vertical micro-programming, which is a method to optimize encoding and compress signals in the control memory. In contrast, horizontal micro-programming lacks such optimizations. The idea is that by encoding signals, one can efficiently manage memory usage. For example, if an output has 16 bits, using a 4:16 decoder will optimize the encoding strategy, compressing the amount of data that needs to be handled. This sets the foundation for understanding how control signals can be organized to be more efficient.

Think of organizing a closet with many clothes. A vertical micro-program is like arranging clothes by type (e.g., shirts, pants, dresses) in separate bins to save space and make finding items faster. A horizontal approach would be throwing all clothes into one large bin, making it easy to access but cluttered and wasteful of space.

So, for example, this is one word of the control memory or this is the format of the control memory word. So, 𝑃𝐶 ,𝑃𝐶 ,𝑀𝐷𝑅 ,𝑀𝐷𝑅 all these values are there. Now, I encode it. 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.

In this chunk, the approach to encoding control memory is further elaborated with a specific example. It discusses a control memory word format and how a decoder is used to determine how many bits need to be controlled. A 3:8 decoder indicates the size of the memory required to control the signals. Specifically, if there are 8 signals to control, the memory size needed is just 3 bits, reducing the space required significantly.

Imagine you have a DVD collection. Instead of keeping all DVDs in one big case (which takes up a lot of space), you use a small organizer that separates them by genre (like action, comedy, drama) – essentially a 'decoder' that tells you exactly where to find your favorite movies without cluttering the space.

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. Say for example generally we know that what happens basically we always have program counter out and memory address register in. So here what will be happen first you will have to give the value called 001. Which will make 𝑃𝐶 𝑃𝐶 = 1, then the program counter there will be some stable register or 1-bit flip flop which will hold the value, but it has to be a 1.

This chunk highlights a key disadvantage of the vertical micro-programming approach. Due to the encoding optimization, only one control signal can be activated at a time; for example, while activating the Program Counter (PC), the Memory Address Register (MAR) cannot also be activated. This limitation leads to slower operation because multiple steps must be taken to activate different components sequentially. It illustrates the trade-off between memory optimization and speed.

Consider a single-lane toll booth on a highway. Only one car can pass through at a time, creating a queue. Even if there are several cars waiting to pay (like multiple signals), each can only go one after the other, leading to delays. If there were multiple lanes (horizontal approach), cars could pass simultaneously, speeding up the process.

Now, what happens now, but still now 𝑃𝐶 is also equal to 1 this is also equal to 1. Now, we have to give a time step where you reset actually both...

This chunk discusses the need to reset control signals after they've been activated. With vertical micro-programming, the systems become slower as one signal is initialized, and after its duty, there is a necessary reset before another can be activated. This aspect illustrates the complexity and time-consuming nature of maintaining states in a vertical architecture, compared to a horizontal micro-program that can maintain multiple active states simultaneously.

Think of a light switch in a room where only one bulb can be on at a time. Once you switch a bulb off, you have to wait until it's off before switching on another one. In contrast, a room filled with multiple light switches allows multiple bulbs to be on at once, keeping the space well-lit without the need for constant resetting.

So, if we have a lot of 0's then such problems will become in such some kinds of number of stages will be less, but if we have more number of 1's then making them simultaneously 1 is not possible...

This chunk provides a comparative analysis of vertical and horizontal micro-programming techniques. Vertical programming is efficient in terms of memory when there are many zeros (unused signals), but it suffers from speed issues when needing to activate multiple ones simultaneously. In a horizontal approach, on the other hand, multiple signals can be active at once, offering faster execution times but potentially leading to wasted memory and resource utilization.

Imagine a busy restaurant kitchen. In a vertical setup, only one chef can be chopping while another is stirring, leading to delays. If the setup is horizontal, multiple chefs can work on different tasks at the same time – improving efficiency but possibly leading to a crowded workspace where some are not utilized effectively.

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...

This final chunk summarizes the overall discussion on the trade-offs between horizontal and vertical micro-programming architectures. It mentions that horizontal requires fewer instructions and is faster, whereas vertical offers memory efficiency but at a slower pace and with more complex signal handling. The overview encourages students to consider these dynamics as they explore further instruction execution in future discussions.

Think of deciding how to build a house. A horizontal approach might use many materials to construct quickly but can lead to wasted space. A vertical approach economizes on materials but takes longer to build and requires careful planning to ensure every component aligns, showing the fundamental trade-offs and planning in any structured project.

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