Computer Storage Devices

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Questions and Answers

What is the limitation of the simplest view of sector organization?

It is not efficient for reading a series of sectors (correct)

It is only used for large files

It is only used for small files

It does not account for physical contiguity of sectors

What is the purpose of interleaving in sector organization?

To decrease the file manager's job

To increase the disk controller's processing time

To store sectors in a contiguous manner

To leave an interval of several physical sectors between logically adjacent sectors (correct)

What is a cluster in the context of sector organization?

A fixed number of contiguous sectors (correct)

A fixed number of contiguous cylinders

A fixed number of contiguous tracks

A fixed number of contiguous files

What is the purpose of the File Allocation Table (FAT)?

To map the logical sectors to their corresponding physical clusters Signup and view all the answers

What is an extent in the context of sector organization?

A contiguous series of clusters Signup and view all the answers

What happens when the disk controller is processing the received information?

It takes a certain amount of time to process the received information Signup and view all the answers

Why do we use clustering in sector organization?

To improve performance by minimizing seeking Signup and view all the answers

What happens when the number of extents in a file increases?

The file becomes more fragmented Signup and view all the answers

What is the primary advantage of direct access storage devices (DASDs)?

They can access data directly. Signup and view all the answers

What is the purpose of a sector on a disk?

To serve as the smallest addressable portion of a disk. Signup and view all the answers

What is the process of moving the arm that holds the read/write heads called?

Seeking. Signup and view all the answers

What determines the number of tracks on a surface of a disk?

The density of bits on the disk surface. Signup and view all the answers

What is the advantage of accessing data on a single cylinder?

It reduces the amount of seeking required. Signup and view all the answers

What is the role of the buffer in the process of reading data from a disk?

It temporarily holds the contents of a sector. Signup and view all the answers

Why are floppy disks not suitable for storing large amounts of data?

They hold relatively little data. Signup and view all the answers

What is the relationship between the number of platters and the number of tracks per cylinder?

The number of tracks per cylinder is twice the number of platters. Signup and view all the answers

Study Notes

Direct Access Storage Devices (DASDs)

Disk drives are classified as DASDs because they allow direct access to data.
This is in contrast to serial devices, which use media like magnetic tape and require sequential access.

Floppy Disks

Floppy disks are inexpensive, but slow and have limited data storage capacity.
They are suitable for backing up individual files or small amounts of data, and for transporting data.

Disk Storage

Data is stored on the surface of one or more platters.
The data is organized in successive tracks on the surface of the disk.
Each track is divided into a number of sectors.
A sector is the smallest addressable portion of a disk.

Sector Access

When a read statement is called, the computer operating system:
- Finds the correct surface, track, and sector.
- Reads the entire sector into a buffer in memory.
- Finds the requested byte within that buffer.

Cylinders

Tracks directly above and below one another form a cylinder.
The significance of a cylinder is that all data on it can be accessed without moving the arm that holds the read/write heads.
Moving the arm is called seeking, which is usually the slowest part of reading data from a disk.

Physical Placement of Sectors

The simplest view is that sectors are adjacent, fixed-sized segments of a track that hold a file.
However, physically, sectors may not be adjacent to improve performance.
Interleaving is used to leave an interval of several physical sectors between logically adjacent sectors.
Clusters are used to group contiguous sectors together to improve performance.

Clusters

A cluster is a fixed number of contiguous sectors.
The file manager uses a file allocation table (FAT) to map logical sectors to physical clusters.
The FAT contains a list of all clusters in a file, ordered according to the logical order of the sectors they contain.

Extents

An extent is a contiguous group of clusters on a disk.
If a file consists of only one extent, it means that all its sectors are physically contiguous.
As the number of extents in a file increases, the file becomes more fragmented, leading to slower performance.

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Description

Learn about the characteristics of disk drives, serial devices, and floppy disks. Understand the differences between direct access and serial access storage devices.