First Fit program in Python

March 27, 2022

First Fit Program in Python

Memory management is one of the most important tasks of the operating system. Processes are allocated empty memory blocks as per the process demands. This allocation takes place dynamically at the run time.

How first fit works?

Whenever a process (p1) comes with memory allocation request the following happens –

OS sequentially searches available memory blocks from the first index
Assigns the first memory block large enough to accommodate process

Whenever a new process P2 comes, it does the same thing. Search from the first index again.

Methods discussed

We will look at two different methods –

Method 1 – Blocks allowed to keep just one single process
Method 2 – Blocks allowed to keep multiple processes, if partitioned fragmentation big enough for new processes

Method 1

Run

def FirstFit(block_Size, blocks, process_Size, proccesses):
    # code to store the block id of the block that needs to be allocated to a process
    allocate = [-1] * proccesses
    occupied = [False] * blocks

    # Any process is assigned with the memory at the initial stage

    # find a suitable block for each process
    # the blocks are allocated as per their size

    for i in range(proccesses):
        for j in range(blocks):
            if not occupied[j] and (block_Size[j] >= process_Size[i]):
                # assign the block j to p[i] process
                allocate[i] = j
                occupied[j] = True
                break

    print("Process No. Process Size Block No.")

    for i in range(proccesses):
        print(str(i + 1) + "\t\t\t" + str(process_Size[i]) + "\t\t\t", end=" ")

        if allocate[i] != -1:
            print(allocate[i] + 1)
        else:
            print("Not Allocated")


# Driver code

block_Size = [100, 50, 30, 120, 35]
process_Size = [20, 60, 70, 40]
m = len(block_Size)
n = len(process_Size)

FirstFit(block_Size, m, process_Size, n)

Output:

Process No. Process Size Block No.
1	    20		1
2	    60		4
3	    70		Not Allocated
4	    40		2

Method 2

This allows multiple processes to share the same block space if the size is enough to keep another process.

Run

def FirstFit(block_Size, m, process_Size, n):
    # code to store the block id of the block that needs to be allocated to a process
    allocate = [-1] * n

    # Any process is assigned with the memory at the initial stage

    # find a suitable block for each process
    # the blocks are allocated as per their size

    for i in range(n):
        for j in range(m):
            if block_Size[j] >= process_Size[i]:
                # assign the block j to p[i] process
                allocate[i] = j

                # available block memory is reduced
                block_Size[j] -= process_Size[i]
                break

    print("Process No. Process Size Block No.")

    for i in range(n):
        print(str(i + 1) + "\t\t\t" + str(process_Size[i]) + "\t\t\t", end=" ")

        if allocate[i] != -1:
            print(allocate[i] + 1)
        else:
            print("Not Allocated")


# Driver code

block_Size = [100, 50, 30, 120, 35]
process_Size = [20, 60, 70, 40]
m = len(block_Size)
n = len(process_Size)

FirstFit(block_Size, m, process_Size, n)

Output:

Process No. Process Size Block No.
1	  20	 1
2	  60	 1
3	  70	 4
4	  40	 2

Memory Management Introduction
Partition Allocation Method
1. First Fit in OS
  1. Program in C | C++ | Java | Python
2. Best fit
  1. Program in C | C++ | Java | Python
3. Worst fit
  1. Program in C | C++ | Java | Python
4. Next fit
  1. Program in C | C++ | Java | Python
5. First fit best fit worst fit in OS Example
Buddy- System Allocator
Paging
1. Types of Paging
Fragmentation
Mapping Virtual address to Physical Address.
Virtual Memory
Demand Paging
Implementation of Demand paging and page fault
Segmentation
Page Replacement Algorithms
Thrashing
Belady’s Anomaly
Static vs Dynamic Loading
Static vs Dynamic Linking
Swapping
Translational Look Aside Buffer
Process Address Space
Difference between Segmentation and Paging

First Fit program in Python