External Memory Overview

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Questions and Answers

What is another name for external memory?

Volatile memory

Cache memory

Primary memory

Secondary memory (correct)

Which of the following is NOT a category of external memory?

Optical memory

Flash memory (correct)

Magnetic disk

Magnetic tape

What material is commonly used for constructing the substrate of magnetic disks?

Plastic

Glass

Copper

Aluminium (correct)

What advantage does glass substrates provide over traditional materials in magnetic disks?

Increased reliability Signup and view all the answers

In a magnetic disk, what is the role of the write head?

To record magnetic patterns on the disk Signup and view all the answers

When reading data from a magnetic disk, what does the read head generate?

Electric currents Signup and view all the answers

What happens to the information stored in external memory when the computer is switched off?

It remains intact Signup and view all the answers

Which component is essential for the operation of both reading and writing on magnetic disks?

Rotating platter Signup and view all the answers

What is the primary use of CD-ROM?

Storing computer data Signup and view all the answers

What happens when a CD-ROM encounters an error in the stored data?

The error is reflected in the produced output Signup and view all the answers

How is data organized on a CD-ROM?

In sectors and tracks Signup and view all the answers

What differentiates CD-R from CD-ROM?

CD-R allows for one-time recording, while CD-ROM is strictly for computer data Signup and view all the answers

What material is NOT a component of a CD-R?

Ferromagnetic disk coating Signup and view all the answers

How does the speed of the disk rotation vary when accessing sectors on a CD?

Slower for outer edge sectors and faster for inner sectors Signup and view all the answers

What is the role of the organic polymer dye in a CD-R?

To change reflectivity when exposed to light Signup and view all the answers

What is a characteristic feature of a CD-ROM's track structure?

Variability in the number of sectors across inner and outer tracks Signup and view all the answers

What is the resolution provided by a standard DVD?

720x480 pixels Signup and view all the answers

Which recording technique is most commonly used in modern tape systems?

Serial recording Signup and view all the answers

What is the purpose of inter-record gaps in serial recording on tape?

To separate data blocks Signup and view all the answers

How does a tape drive access data in comparison to a disk drive?

Sequential access Signup and view all the answers

When recording data to tape using serial recording, what happens when the end of the tape is reached?

The head is repositioned to record in the opposite direction Signup and view all the answers

What allows a disk drive to access desired data without reading all sectors sequentially?

Direct access capability Signup and view all the answers

Which of the following is true about magnetic tape in the context of memory hierarchy?

It is a type of secondary memory Signup and view all the answers

What characterizes linear tape technology developed in the late 1990s?

It is a type of cartridge system Signup and view all the answers

What is the primary difference between CD-RW and CD-R?

CD-RW can be rewritten and reused. Signup and view all the answers

Which state of the alloy in CD-RW is used to absorb light?

Amorphous state Signup and view all the answers

What is one major technological advancement of DVDs over CDs?

DVDs use a shorter wavelength laser beam. Signup and view all the answers

How is the crystalline state in CD-RW achieved?

By maintaining a high temperature for an extended period. Signup and view all the answers

What leads to the registration of digital data in a CD-RW?

The combination of crystalline and non-crystalline areas. Signup and view all the answers

What is the storage capacity of a standard single-layer DVD?

4.7GB Signup and view all the answers

Which property allows DVDs to accommodate more data compared to CDs?

Use of multiple layers and sides. Signup and view all the answers

What happens to data stored on a CD-RW during the annealing process?

Data can be rewritten. Signup and view all the answers

What is the primary advantage of RAID 3 compared to its predecessors?

It is resistant to disk failures. Signup and view all the answers

What is the main disadvantage of RAID 3's performance during a disk failure?

The throughput significantly decreases. Signup and view all the answers

Which factor primarily slows down write speeds in RAID 3?

Need for checksum calculation. Signup and view all the answers

How does RAID 4 manage parity data differently from RAID 3?

It confines all parity data to a single disk. Signup and view all the answers

What is a required configuration for RAID 4 to function properly?

At least three disks. Signup and view all the answers

Why is RAID 3 rarely used in practical applications?

It is not cost-effective and reliable. Signup and view all the answers

In what scenario is RAID 3 most effective?

For large files accessed by a small number of users. Signup and view all the answers

What is the primary characteristic of RAID 4's data handling?

Block-level striping. Signup and view all the answers

Study Notes

External Memory

External memory, also known as secondary memory or backing store, is used for storing large amounts of data.
Its capacity can be in hundreds of megabytes or even gigabytes.
Data stored in external memory is not lost when the computer is switched off.

Types of External Memory

Magnetic Disk: A circular platter with a magnetic coating used for data storage.
- Traditionally made of aluminum or aluminum alloy, but glass substrates offer improved reliability, reduced read-write errors, and greater shock resistance.

Magnetic Read and Write Memory

Magnetic disks are a key component of external memory, used in systems like supercomputers, personal computers, and mainframes.
Data is written and read by a magnetic head that generates a magnetic field when electricity flows through it.
Write heads record data as different magnetic patterns for positive and negative currents.
Read heads generate an electric current when the disk's surface passes under them, with the polarity of the current matching the recorded data.

RAID 3

RAID 3, also known as Bit-level striping, involves data striping across multiple disks with dedicated parity calculation.
It provides high throughput for large data transfers and is resistant to disk failure.
However, it suffers from slow write speeds due to checksum calculations, slow performance in case of disk failure, and the dedicated disk for checksums acting as a bottleneck.
RAID 3 is rarely used in practice.

RAID 4

RAID 4, also known as Block-level striping, is similar to RAID 3, but uses block-level data striping instead of byte-level striping.
It uses a single disk for parity data and also requires hardware support for parity calculations.
Involves grouping data into blocks and writing the parity for each block separately.
Minimal implementation requires at least three disks.

Optical Memory

Optical memory, such as CDs and DVDs, has become a popular alternative to older magnetic storage methods.
Compact disks (CDs) and digital versatile disks (DVDs) have similar appearances but differ in storage capacity, with DVDs having a larger storage size.
Both CDs and DVDs utilize a laser beam to read and write data. The wavelength of the laser beam used by DVDs is shorter than that used by CDs, allowing for tighter data storage.

Types of CDs

CD-ROM: A read-only memory format primarily used for storing computer data.
CD-R: A write-once read-many format allowing single-time recording on a disk.
CD-RW: A rewritable format that allows multiple writing cycles on a disk.

Digital Versatile Disk (DVD)

DVDs were first launched in 1996.
They offer a much larger storage capacity than CDs.
DVDs utilize a shorter wavelength laser beam and smaller data pits, allowing for higher data density.
By using two-sided or two-layered disks, storage capacity can be further increased.

Magnetic Tape

Magnetic tape is a flexible polyester tape coated with a magnetizable material for data storage.
Most modern systems use serial recording, where bits are stored along each track.
Inter-record gaps separate blocks of data on the tape.
Tape drives are sequential access devices, requiring rewinding to reach desired data.

Linear Tape Open (LTO)

A cartridge system developed in the late 1990s.
An alternative to traditional tape systems, offering various features.
LTO systems are commonly used in data backup and archiving.

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Description

Explore the concept of external memory, which is crucial for storing large amounts of data in computers. This quiz covers types of external memory, specifically focusing on magnetic disks and their functionality in data storage systems. Test your understanding of how data is written and read using magnetic fields.