1. File systems are usually implemented in a layered or modular structure. Explain layer structure in the file system.2. There are several ways files are allocated on disk space, namely contiguous, linked or indexed. Explain the three methods of file allocation above and give examples.

1. Layered Structure in the File System:

The layered structure in a file system is a design principle that helps in managing complexity. It is a hierarchical structure where each layer provides services to the layer above it and uses services from the layer below it. Here are the layers in a typical file system:

• Application Programs: This is the topmost layer where users interact with the system. It includes word processors, spreadsheets, compilers, etc.

• Logical File System: This layer manages metadata information. Metadata includes file size, file type, file location, file permissions, etc.

• File-Organization Module: This layer translates logical addresses into physical addresses. It manages free space and allocates space for new files.

• Basic File System: This layer deals with the placement of files on the disk and disk space management.

• I/O Control: This layer manages the memory buffers and devices that perform I/O operations.

• Devices: This is the bottom layer that interacts with peripheral devices like disk drives.

2. Methods of File Allocation:

   • Contiguous Allocation: In this method, each file occupies a contiguous address space on disk. For example, if a file requires N blocks, those N blocks will be stored together on the disk. This method allows for high performance by supporting both sequential and direct access. However, it can lead to issues like external fragmentation and inefficient disk space utilization.

   • Linked Allocation: In this method, each file is a linked list of disk blocks. The blocks may be scattered anywhere on the disk. Each block contains a pointer to the next block in the file. This method eliminates the issue of external fragmentation but it is inefficient for direct access because to access a block, we need to traverse from the first block.

   • Indexed Allocation: In this method, an index block is created for each file. The index block contains pointers to the blocks of the file. This method supports direct access and eliminates external fragmentation. However, it can be inefficient for small files as it requires an index block.