L-5.5: First Fit, Next Fit, Best Fit, Worst fit Memory Allocation | Memory Management | OS

Summary

This video script delves into four algorithms used in contiguous memory management for process allocation: First Fit, Next Fit, Best Fit, and Worst Fit. First Fit allocates the first sufficient hole, minimizing search time but potentially creating large leftover spaces. Next Fit, a variation of First Fit, starts searching from the last allocated hole, enhancing efficiency. Best Fit selects the smallest hole just large enough for a process, reducing internal fragmentation but at the cost of speed due to extensive searching. Worst Fit chooses the largest hole, leaving the most space, which might accommodate more processes but can lead to inefficient memory use. The script emphasizes understanding these algorithms for effective memory management.

Takeaways

• 📌 **Four Memory Allocation Algorithms**: The script discusses First Fit, Next Fit, Best Fit, and Worst Fit algorithms used in contiguous memory management.
• 🔍 **First Fit**: Allocates the first hole in memory that is large enough to fit the process, optimizing for speed and simplicity.
• 🔄 **Next Fit**: A variation of First Fit, it starts searching for the next hole from the last allocated one, improving search efficiency.
• 🎯 **Best Fit**: Searches the entire list to find the smallest hole just large enough for the process, minimizing internal fragmentation but at the cost of speed.
• 🏁 **Worst Fit**: Selects the largest hole available, leading to maximum internal fragmentation but allowing for potential future allocations in large holes.
• 🔑 **Internal Fragmentation**: Best Fit aims to minimize it by finding the most fitting hole, whereas Worst Fit maximizes it by choosing the largest hole.
• 🚀 **Speed Considerations**: First Fit is the fastest due to its straightforward approach, while Best Fit and Worst Fit are slower because they require searching the entire list.
• 🔄 **Next Fit Advantage**: It improves upon First Fit by starting the search from the last allocated hole, thus saving time on subsequent allocations.
• 📉 **Fragmentation Issues**: Both Best Fit and Worst Fit can lead to fragmentation, but in different ways—Best Fit creates many small holes, while Worst Fit leaves large ones.
• 📚 **Educational Content**: The script is educational, aiming to clarify how different memory allocation strategies work and their implications.
• 👍 **Engagement Call**: The speaker encourages viewers to like, share, and subscribe, indicating the script is part of a series or channel dedicated to educational content.

Q & A

What are the four algorithms discussed in the script for contiguous memory management?

The four algorithms discussed for contiguous memory management are First Fit, Next Fit, Best Fit, and Worst Fit.

How does the First Fit algorithm allocate memory for a process?

The First Fit algorithm allocates memory by finding the first hole or partition that is big enough to accommodate the process, starting the search from the beginning of the memory.

What is the main difference between First Fit and Next Fit algorithms?

The main difference is that Next Fit starts searching for the next hole from the last allocated hole, whereas First Fit always starts from the beginning of the memory.

How does the Best Fit algorithm differ from the First Fit and Next Fit algorithms?

The Best Fit algorithm searches the entire list of holes to find the smallest hole that can accommodate the process, aiming to minimize internal fragmentation.

What is the primary goal of the Worst Fit algorithm?

The primary goal of the Worst Fit algorithm is to select the largest hole to accommodate the process, which results in the maximum leftover space.

Why might the Best Fit algorithm create small holes that cannot accommodate future processes?

The Best Fit algorithm might create small holes because it prioritizes minimizing the leftover space after allocation, which can lead to tiny holes that are too small for future processes.

What is a potential advantage of the Worst Fit algorithm over the Best Fit algorithm?

A potential advantage of the Worst Fit algorithm is that it leaves larger holes after allocation, which might be more suitable for accommodating larger processes in the future.

Why are the Best Fit and Worst Fit algorithms considered slower compared to the First Fit and Next Fit algorithms?

The Best Fit and Worst Fit algorithms are slower because they need to search the entire list of holes to find the optimal hole, whereas the First Fit and Next Fit algorithms stop searching once they find a suitable hole.

What is the main disadvantage of the First Fit algorithm as discussed in the script?

The main disadvantage of the First Fit algorithm is that it might create large holes that cannot be utilized by smaller processes, leading to inefficient memory usage.

How does the Next Fit algorithm improve upon the First Fit algorithm in terms of search efficiency?

The Next Fit algorithm improves search efficiency by starting the search from the last allocated hole, thus avoiding the need to search from the beginning each time.

Outlines

00:00

🧠 Contiguous Memory Management Algorithms

This paragraph introduces four algorithms used in contiguous memory management for process allocation. These algorithms are First Fit, Next Fit, Best Fit, and Worst Fit. The discussion focuses on how to allocate memory to processes in the presence of already existing processes and available memory holes. The First Fit algorithm is explained in detail, where the memory allocation starts from the first suitable hole that can accommodate the process size. An example is given with a process P1 of 15KB size being allocated to a 25K hole, highlighting the efficiency and simplicity of the First Fit method.

05:03

🔄 Next Fit and Best Fit Algorithms

The Next Fit algorithm is described as a modification of the First Fit, where the search for a suitable hole starts from the last allocated hole, thus improving search efficiency. The Best Fit algorithm is then introduced, which searches the entire list of holes to find the one that minimizes internal fragmentation, i.e., the hole that leaves the smallest leftover space after allocation. The disadvantages of Best Fit, such as creating too many small holes that cannot accommodate larger processes and the time-consuming search process, are also discussed.

10:06

🔄 Worst Fit Algorithm and Real-life Application

The Worst Fit algorithm is explained as the opposite of Best Fit, where the goal is to find the largest hole to accommodate a process, thus leaving the maximum possible leftover space. The paragraph discusses the advantages of Worst Fit in terms of leaving larger holes that can still accommodate more processes, contrasting with the small holes created by Best Fit. The slow performance of both Best Fit and Worst Fit due to the need to search the entire list of holes is mentioned. The paragraph concludes with a discussion on the practical implications of these algorithms, suggesting that while First Fit is the most convenient, the best choice can depend on the specific scenario.

15:09

📚 Practical Considerations and Conclusion

This final paragraph emphasizes the importance of understanding how these memory allocation algorithms work, rather than memorizing which one is best in every situation. It suggests that the choice of algorithm can depend on the specific requirements of a given scenario. The paragraph encourages viewers to like, share, and subscribe to the channel for more content, highlighting the educational value of the video.

Keywords

💡Contiguous Memory Management

Contiguous Memory Management refers to the allocation of memory in a way that processes are placed in adjacent blocks of memory. This is a method used in operating systems to manage the physical memory efficiently. In the video, this concept is central as it discusses how different algorithms allocate memory to processes in a contiguous manner, ensuring that the processes are stored in continuous memory locations.

💡First Fit

First Fit is one of the memory allocation algorithms discussed in the video. It allocates the first hole or partition in memory that is large enough to fit the process. The video explains that this method is simple and fast because it stops searching as soon as it finds a suitable hole, which minimizes the search time. An example from the script is when a process of 15KB needs to be allocated, First Fit would place it in the first hole of 25KB it encounters.

💡Next Fit

Next Fit is a variation of the First Fit algorithm. It starts searching for a hole to allocate a process from the point where the last allocation ended. This method is slightly more efficient than First Fit as it doesn't start the search from the beginning each time, thus saving some time. The video uses an example where after allocating a process with First Fit, Next Fit would begin its search from the last allocated hole for the next process.

💡Best Fit

Best Fit is an allocation algorithm that searches the entire list of holes to find the smallest one that can accommodate the process, aiming to minimize internal fragmentation. The video explains that while this method results in less wasted space, it can lead to the creation of many small holes that might not be useful for larger processes. An example given is allocating a 15KB process into a 20KB hole, leaving only 5KB of unused space.

💡Worst Fit

Worst Fit is the opposite of Best Fit. It selects the largest hole available to accommodate a process, which results in the most leftover space. The video points out that while this might seem wasteful, it can be advantageous for future allocations as it leaves larger spaces that might be suitable for larger processes. An example used is placing a 15KB process into an 85KB hole, leaving a significant amount of space.

💡Internal Fragmentation

Internal fragmentation refers to the unused space within a memory partition that is too small to be usefully allocated to another process. The video discusses how Best Fit aims to minimize this by finding the smallest suitable hole, but it can also lead to the creation of many small unusable spaces. In contrast, Worst Fit, by leaving larger spaces, might reduce the occurrence of internal fragmentation.

💡Hole

In the context of the video, a 'hole' refers to a block of free memory within the contiguous memory. The algorithms discussed are all about how to allocate these holes to processes. The size and number of holes can significantly affect the efficiency of memory usage and the choice of allocation algorithm.

💡Memory Allocation

Memory allocation is the process of assigning portions of a computer's memory to processes. The video focuses on various algorithms for memory allocation, emphasizing how they determine where and how processes are placed in memory. This is crucial for the efficient use of memory resources in an operating system.

💡Pointer

A pointer, as mentioned in the context of Next Fit, is a variable that stores the memory address of another variable. In the video, it is used to keep track of the last allocated hole, which helps in starting the search for the next hole from that point, thus optimizing the allocation process.

💡Efficiency

Efficiency in this video pertains to how well the memory allocation algorithms use memory space and how quickly they perform their task. It is contrasted between the simplicity and speed of First Fit versus the more thorough but slower Best Fit and Worst Fit algorithms.

💡Search Time

Search time is the duration it takes for an algorithm to find a suitable hole for a process in the memory. The video highlights that First Fit and Next Fit have less search time because they do not require searching the entire list of holes, unlike Best Fit and Worst Fit, which must evaluate all possible options.

Highlights

Four main algorithms for contiguous memory management are discussed: First Fit, Next Fit, Best Fit, and Worst Fit.

First Fit allocates the first hole that is big enough for the process.

Next Fit is a modified version of First Fit, starting the search from the last allocated hole.

Best Fit searches the entire list to find the hole that minimizes internal fragmentation.

Worst Fit selects the largest hole, aiming to maximize the leftover space after allocation.

First Fit is simple and fast but may lead to large holes if not managed properly.

Next Fit improves upon First Fit by starting the search from the last allocated hole, reducing search time.

Best Fit minimizes internal fragmentation but can create small holes that are difficult to utilize.

Worst Fit can accommodate more processes due to larger leftover spaces but is slower due to searching the entire list.

Best Fit and Worst Fit are exact opposites in their approach to memory allocation.

The choice of algorithm can significantly impact memory utilization and fragmentation.

First Fit is considered the most convenient method due to its simplicity and speed.

The algorithms are important for managing memory efficiently in operating systems.

Understanding the working of these algorithms is crucial for addressing memory allocation questions.

The video provides a practical guide for students preparing for exams like GATE.

The presenter encourages viewers to like, share, and subscribe for more content.

Transcripts

Various allocation methods in Contiguous Memory Management. So basically we are using 4 algorithms

how we are allocating the memory to the processes. Means in our memory

as many processes are already present and as many available holes we have,

how we allocate processes in those holes. So basically there are 4 algorithms,

First Fit, Next Fit, Best Fit, and Worst Fit.

So let's examine this according to this diagram,

this is showing a process has already occupied this memory area. This is what,

already there is a process let's say process10, there is one process11, a process12,

process13, process14, process15. So these processes are already there in the memory and

this is representing the holes, these are the holes, means leftover space.

So how we can manage this leftover space? We will be using these algorithms.

So let's start with the first, First Fit algorithm.

According to the First Fit algorithm, allocate the first hole or partition,

we can say partition also but majority we use it to manage the holes.

So allocate the first hole that is big enough means let's say there is a process P1,

and process size is 15K.

Process size is 15KB.

So if process of 15K is coming, so according to the First Fit what it will check?

It will simply check the first location that is big enough which can hold the 15K.

Means it will start from this, so this is already occupied, occupied, occupied,

this is the empty space. So this is one hole, what is the size of this hole? 25K.

So 25K can easily accommodate the 15K, so according to the First Fit,

it will simply stop searching, which search? Hole searching it will stop,

and simply allocate P1 to this partition or we can say hole.

Means where will it accommodate P1? In this space. First such hole

where I can fit that process, that we'll call the First Fit. It is easiest.

Because here my searching time is also very less, I'm not searching the entire list,

when I get the first hole, I will accommodate the process there.

According to the Next Fit, Next Fit is modified version of the First Fit.

So in Next Fit also we are doing same, same as first fit but start searching

always from the last allocated hole. Means the last allocated hole given to some process

we will keep a pointer on that. Let's say that according to first fit I put P1 here,

so I allocated P1 here. Now here a pointer, I will keep a pointer at this area.

That pointer will help with what? Next time if a process comes,

let's say process comes P2, one more process comes P2 and size of P2 is let's say 18K.

Size of P2 is 18K, so from where it will start searching?

It will not start searching from the beginning.

It will start searching from the last value or last space where the process was allocated.

Means last where it was? On this hole, so it will start searching from here

and whatever the next, let's say 40K is enough, in 40K we can easily put 18K,

so this area will be taken by P2. So advantage of Next Fit is that

we need not search from the beginning again and again,

whatever last hole I gave to some process from that hole next we will start

for the empty hole means we will start searching for the next empty hole so that

I can accommodate next process in that.

So here according to Next Fit I will again not start from zero to search,

where will I start from? From this hole. Because this hole I had already given in First Fit

so I will next start form 40K. In 40K I can easily accommodate process of 18K

so I will put P2 here. This is the concept of the Next Fit.

Third one is Best Fit, what is the concept of Best Fit? From the name it is clear,

it will search the entire list and it will try to search that hole which will lead to

minimum internal fragmentation. The main thing is that let's say my process is

Let's start this again, if process size is 15K.

Size of process is 15K.

Then 15K process according to the First Fit I can put in this.

According to the Next Fit also I can put in this. But according to Best Fit,

although according to Best Fit also in this already 15K can be accommodated in this.

But it will search the entire list, let's say 40K, it can be accommodated in 40K also

but the leftover space is very huge. So remaining portion should be minimum,

it will try to search for that hole. So at last where will it come? In 20K.

20K can accommodate P1? Yes, 20K can accommodate P1 easily. And what is the leftover space?

If I allocate P1 here, so if P1 is allocated then how much is my leftover space? 5K.

Because remaining area is taken by what? P1. P1 takes the remaining area,

so leftover space is what? 5K.

So it will search the entire list, it will search all holes and choose that hole

in which if I put that process then remaining memory, remaining portion will be least.

This is the concept of the Best Fit. So that my internal fragmentation should be minimum in that case.

According to the Worst Fit, what we do in Worst Fit, we simply select the largest hole.

Means in this also we will search the entire list, but which process we will put in it?

Or in which hole we will put the process? Where my leftover space is maximum.

Means this is exact opposite of Best Fit, it is reverse of Best Fit, so if size of P1 is 15K

then I can put it here also, here also, here also, different places.

But according to the Worst Fit where will I put P1? In this hole.

Because when P1 is put here, P1 is accommodated here. So how much is remaining portion?

Rest of the portion is 85K, which is leading to the maximum memory leftover.

So means according to the Worst Fit where we put any process? Where my left space,

after putting that process my hole size is very big. Now if these are compared

then First Fit is easiest method, very simple. It is very simple to implement and very fast.

The advantage is it is very fast. Because it is directly searching for the first hole

that is big enough to hold my process. It has nothing to do whether leftover space is

high or low, if a process can be accommodated by a hole then the first hole found

it will allocate that process in it.

So here my advantage is simple, it is fast but what is the disadvantage here?

It is possible that disadvantage may be that the remaining portion, the remaining hole,

let's say if I accommodate P1 here then the remaining portion, it will create holes,

big holes it can create. Means remaining you see if I put 15K here,

means if I accommodate P1 here, then how much remaining space I have?

Further hole of 10K remains.

Now in this 10K hole if some process of 10K comes then I can accommodate in this,

but if processes of large size are coming then I cannot accommodate in this.

So this is the advantage of the First Fit. Next Fit is same according to the First Fit.

But one more advantage is First Fit will always start searching from zero,

as soon as first slot is found, first hole is found, it will put the process in that.

But in Next Fit we did little faster, how we made fast? As soon as we put P1 here,

we put a pointer here, now next time when we search for some hole then

we will start searching from this point, we will not start again form zero.

So in Next Fit also same, when one more process comes,

let's say if one more process of 15K comes then which is the next hole found? This hole.

What is the size? 40K. And what is the size my process? 15K.

So I can easily put the 15K in this.

Third one is Best Fit. In Best Fit what advantage I get here is that

in this internal fragmentation will be very less. Means the portion that will be left laterwards

will be a very small portion. But in a way this can be disadvantage also.

Let's say that a process comes, size of process is

if size of process is 35K.

Then according to the Best Fit I will put in this slot, I can put in this also

because 100K can also accommodate, but Best Fit says that after putting a process in the hole

remaining space should be the least. So according to that rule I will simply put this

let's say the process is P2, this P2 process in this.

So what is the remaining portion left? Only 5K. So many times what this Best Fit does

it creates such small, tiny holes that in it I may not be able to further accommodate a process.

because in such small holes it is possible that my process may not accommodate.

Process sizes are little larger and there are tiny holes. In those tiny holes

I cannot put the process but if we see from normal point of view then

we are basically searching for such a hole in which my internal fragmentation is lowest.

And there is one more big disadvantage in Best Fit, the point is it will search the entire list.

It will search the entire list then it will know in which hole to put that process

so that the leftover portion should be least. To know this it will have to compare everywhere.

P2 size is 35K, hole size is 40K, so leftover portion is 5K. Next 100K,

P2 size is 35K, hole size is 100K, leftover portion will be near about 65K which is huge.

So it will search for entire holes, and then it will decide in which hole

I have to put the process so that leftover portion is least. Means here in Best Fit

in advantages we can say that the internal fragmentation

internal fragmentation will be less

or we can say that the remaining holes will be left in very small portions,

but if we see its disadvantages then disadvantage is very slow, this is very slow.

Because it will search for the entire list. Worst Fit is also same.

In Worst Fit what are we searching for? For such a hole in which

my remaining portion is very high. Means if a process comes,

let's say size of process is 15K or let's say size of process is 20K.

So 20K process where we will accommodate according to the Worst Fit?

We will simply accommodate here so that, we put this 20K here, we put this process here,

how much is the remaining portion I have? 80K. So means in Worst Fit an advantage is

that although it is searching for that hole which is big enough and which is leaving the

maximum leftover space. So here maximum leftover space is 80K. But this space is so enough

that if one more process comes or two, three more processes come,

here I can accommodate those also. So means here I don't have so small portions left

of 1-2 bytes, of 1-2 kilobytes in which I don't put the process.

Where was this problem coming? In Best Fit. But in Worst Fit one more 80K hole is left,

now in this 80K hole let's say process P2 comes, P2 size is 10K.

Or let's say size of P2 is let's take 10K.

So according to 10K if I use Worst Fit then again I will put this 10K in this 80K hole,

so that again my leftover portion will again be biggest that is 70K.

So means there are chances of putting more processes in it.

But in Best Fit when you put a process then remaining portion, remaining memory is so less

that in that remaining hole chances of putting further processes are very less.

But in Worst Fit chances are still there because remaining portion is still enough

that you can accommodate another two, three processes. But here also what is the problem?

Slow. Why is it slow? Obviously, it will also search for the entire list,

after searching for the entire list, then it will decide in which hole to put the process

so that remaining memory or remaining space is highest, remaining space is maximum.

In Best Fit remaining space should be minimum, and in Worst Fit remaining space

after putting the process, remaining space in that hole should be maximum.

So Best Fit and Worst Fit are what? Exact opposite. So on this many times

question comes in GATE, like if you are given a diagram that

here how many processes are already occupied and some holes are there, then

according to First Fit, Next Fit, Best Fit or Worst Fit how can I accommodate processes in hole.

So if we see in real life then we can say that First Fit is the most convenient method

because if we simply talk according to time, then among these four, or

basically among these three, because this Next Fit is a modified version of this.

So we can overall compare First Fit, Best Fit and Worst Fit because

this is the modified version of First Fit. So this is the most convenient method

because here time taken is least. But if you normally get a question

then in the question, any scenario may be there. Maybe there Worst Fit works best,

maybe First Fit works best, so you don't need to cram this but

how these algorithms are actually working, that is the important thing.

So if you like the video then please like it, share it and please subscribe my channel, thank you.