Contiguous allocation in Operating Systems - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the sentence to describe contiguous allocation.

Operating Systems

In contiguous allocation, each file occupies [1] block(s) of storage that are next to each other.

Drag options to blanks, or click blank then click option'

Anon-adjacent

Brandom

Cadjacent

Dscattered

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing contiguous with scattered or random allocation.

Thinking files can be stored in non-adjacent blocks in contiguous allocation.

Contiguous allocation means the file's blocks are stored next to each other in adjacent locations on disk.

2fill in blank

medium

Complete the sentence to explain a limitation of contiguous allocation.

Operating Systems

A major limitation of contiguous allocation is [1] fragmentation, which makes it hard to find a large enough free space.

Drag options to blanks, or click blank then click option'

Alogical

Bexternal

Cinternal

Dvirtual

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing external fragmentation with internal fragmentation.

Not understanding that fragmentation affects free space layout.

External fragmentation occurs when free space is split into small pieces scattered around, making it difficult to allocate large contiguous blocks.

3fill in blank

hard

Fix the error in the statement about file access in contiguous allocation.

Operating Systems

In contiguous allocation, direct access to any block of a file is possible by calculating the block's [1].

Drag options to blanks, or click blank then click option'

Aaddress

Bsize

Cname

Dtype

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking size or name helps locate a block directly.

Assuming only sequential access is possible.

The address of the block can be calculated because blocks are stored contiguously, allowing direct access.

4fill in blank

hard

Fill both blanks to complete the formula for calculating the address of the nth block in contiguous allocation.

Operating Systems

Address of nth block = Starting address [1] (n [2] 1) * block size

Drag options to blanks, or click blank then click option'

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication or division instead of addition and subtraction in the formula.

Not subtracting 1 from n before multiplying.

The address is calculated by adding the product of (n - 1) and block size to the starting address.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension that maps file names to their contiguous block ranges.

Operating Systems

file_blocks = { [1]: (start, start + length [2] 1) for [3], (start, length) in files.items() }

Drag options to blanks, or click blank then click option'

Afilename

B-

Cfiles

Dfile

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up variable names in the comprehension.

Using addition instead of subtraction for the block range calculation.

This comprehension creates a dictionary where each file name maps to a tuple showing the start and end block addresses of its contiguous allocation.

Practice

1. What is the main characteristic of contiguous allocation in operating systems?

easy

A. Files are stored in one continuous block of memory.

B. Files are stored in multiple scattered blocks.

C. Files are stored using linked lists.

D. Files are stored in indexed blocks.

Solution

1. Step 1: Understand file storage methods

   Contiguous allocation means storing a file in one continuous block of memory without breaks.

2. Step 2: Compare with other methods

   Other methods like linked or indexed allocation store files in scattered blocks or use pointers.

3. Final Answer:

   Files are stored in one continuous block of memory. -> Option A

4. Quick Check:

   Contiguous allocation = continuous block storage [OK]

Hint: Contiguous means continuous block storage [OK]

Common Mistakes:

• Confusing contiguous with linked allocation
• Thinking files are scattered in contiguous allocation
• Mixing indexed allocation with contiguous

2. Which of the following is the correct way to describe contiguous allocation?

easy

A. Files are divided into fixed-size blocks scattered across memory.

B. Files use pointers to link scattered blocks.

C. Files occupy a single continuous block of memory.

D. Files are stored in a tree-like index structure.

Solution

1. Step 1: Identify the definition of contiguous allocation

   Contiguous allocation means the entire file is stored in one continuous block of memory.

2. Step 2: Eliminate incorrect options

   Options A, B, and D describe other allocation methods like linked or indexed allocation.

3. Final Answer:

   Files occupy a single continuous block of memory. -> Option C

4. Quick Check:

   Continuous block = contiguous allocation [OK]

Hint: Continuous block means contiguous allocation [OK]

Common Mistakes:

• Choosing linked or indexed allocation descriptions
• Confusing fixed-size blocks with contiguous storage
• Assuming pointers are used in contiguous allocation

3. Consider a file system using contiguous allocation. If a file of size 10 blocks is stored starting at block 50, which blocks does it occupy?

medium

A. Blocks 60 to 69

B. Blocks 40 to 49

C. Blocks 51 to 60

D. Blocks 50 to 59

Solution

1. Step 1: Understand starting block and file size

   The file starts at block 50 and occupies 10 continuous blocks.

2. Step 2: Calculate occupied blocks

   Blocks occupied are from 50 up to 50 + 10 - 1 = 59.

3. Final Answer:

   Blocks 50 to 59 -> Option D

4. Quick Check:

   Start 50 + size 10 = blocks 50-59 [OK]

Hint: Start block + size - 1 = last block [OK]

Common Mistakes:

• Off-by-one errors in block range
• Starting count from 1 instead of 0
• Choosing blocks after the last block

4. A file stored using contiguous allocation needs to be extended by 5 blocks, but the next 5 blocks after the file are occupied. What is the main problem here?

medium

A. File cannot be extended because contiguous space is not available.

B. File can be extended by linking scattered blocks.

C. File size can be increased without any issue.

D. File can be moved to another location without fragmentation.

Solution

1. Step 1: Understand contiguous allocation extension

   Files must occupy continuous blocks; extension requires free blocks immediately after the file.

2. Step 2: Analyze the problem

   Since the next 5 blocks are occupied, the file cannot be extended contiguously.

3. Final Answer:

   File cannot be extended because contiguous space is not available. -> Option A

4. Quick Check:

   Extension needs free contiguous blocks [OK]

Hint: Extension needs free continuous blocks [OK]

Common Mistakes:

• Assuming scattered blocks can be linked in contiguous allocation
• Ignoring fragmentation issues
• Thinking file can grow without moving

5. You have a disk with free blocks scattered as follows: 5 blocks free at 0-4, 3 blocks free at 10-12, and 7 blocks free at 20-26. You want to store a file of size 6 blocks using contiguous allocation. Which free space can you use and why?

hard

A. Blocks 10-12, because they are in the middle of the disk.

B. Blocks 20-25, because they have enough continuous free blocks.

C. Blocks 0-4, because they are the first free blocks.

D. No space is available because all free blocks are scattered.

Solution

1. Step 1: Identify free block sizes

   Free blocks are 5 at 0-4, 3 at 10-12, and 7 at 20-26.

2. Step 2: Find a continuous free space of at least 6 blocks

   Only blocks 20-26 have 7 continuous free blocks, enough for 6 blocks.

3. Final Answer:

   Blocks 20-25, because they have enough continuous free blocks. -> Option B

4. Quick Check:

   Need ≥6 continuous blocks, only 20-26 fits [OK]

Hint: Choose free space with enough continuous blocks [OK]

Common Mistakes:

• Choosing smaller free blocks that don't fit file size
• Ignoring the need for continuous blocks
• Assuming scattered free blocks can be combined