Secondary Storage Devices Notes for SSC Exams

Secondary storage devices are a favourite in SSC Computer Knowledge, with questions on the capacity of a CD or a DVD, the type of storage and the working of a hard disk. These secondary storage devices notes for SSC give you the tables of the devices with capacity and practice questions. Read it with the Computer Memory Notes and Computer Hardware Components Notes notes.

What Is Secondary Storage?

• Secondary storage keeps data permanently even when the power is off, so it is non-volatile.
• It is cheaper and bigger but slower than the primary memory (RAM).
• The CPU cannot access it directly; data is first moved to RAM.
• Storage devices are of three types: magnetic, optical and solid state.

Magnetic Storage Devices

The first hard disk was made by IBM in 1956 (IBM 305 RAMAC). A hard disk is accessed directly (randomly), while a magnetic tape is accessed sequentially.

Optical Storage Devices

• CD-ROM is read-only. CD-R can be written once. CD-RW can be written and erased many times.
• The same types exist for DVD: DVD-ROM, DVD-R and DVD-RW.
• Data on an optical disc is stored in tiny pits and lands and is read by a laser.

Solid State Storage

Storage Units and Other Terms

• Order of capacity: KB, MB, GB, TB, PB.
• Cloud storage keeps data on remote servers on the internet, such as Google Drive and OneDrive.
• Formatting prepares a disk to store the data by creating the tracks and the sectors.
• Defragmentation arranges the scattered files of a hard disk to speed it up (not needed for an SSD).
• Backup is a copy of the data kept in a safe place.

Hard Disk Drive in Detail

• A hard disk has one or more platters (metal disks) coated with magnetic material, which spin at 5400, 7200 or more RPM.
• The data is read and written by a read/write head on an arm.
• Each platter surface is divided into tracks (circles) and sectors (parts of the tracks). A group of the same tracks on all platters is called a cylinder. The usual sector size is 512 bytes or 4 KB.
• Seek time is the time to move the head to the correct track; latency is the time for the sector to come under the head.
• Hard disks are connected using SATA (older: IDE or PATA, SCSI).
• Common sizes are 3.5 inch (desktop) and 2.5 inch (laptop).
• RAID (Redundant Array of Independent Disks) joins many disks for speed or safety.

SSD vs HDD

Optical Disc Details

• Optical discs have a spiral track with pits (holes) and lands (flat parts) read by a laser.
• A burner or writer writes the data on a CD-R or DVD-R.
• A disc is protected by a plastic layer, and scratches can damage the data.

Flash and Portable Storage

Magnetic Tape and Backup

• Magnetic tape is the cheapest storage per GB and the best for long-term backup and archives.
• Data on a tape is stored sequentially, so finding a file takes a long time.
• Tape is used in banks, data centres and weather offices for old records.
• Backup types: full backup (all data), incremental backup (only the new changes since the last backup) and differential backup (changes since the last full backup).
• The 3-2-1 rule suggests keeping 3 copies of the data on 2 different media with 1 copy at another place.
• Cloud storage and NAS (Network Attached Storage) are also used for backup.

Storage Capacity Comparison

Important Questions Explained

Question 1: What is the capacity of a standard CD?
Answer: About 700 MB.

Question 2: What is the capacity of a single-layer DVD?
Answer: 4.7 GB.

Question 3: Which storage device uses flash memory and has no moving parts?
Answer: An SSD (solid state drive).

Question 4: Which storage device stores data sequentially?
Answer: Magnetic tape.

Question 5: Which disc uses a blue-violet laser?
Answer: Blu-ray disc.

Question 6: What is the capacity of a 3.5-inch floppy disk?
Answer: 1.44 MB.

Quick Tips to Remember

• Learn the capacity ladder: floppy 1.44 MB, CD 700 MB, DVD 4.7 GB, Blu-ray 25 GB.
• Link SSD with flash memory and no moving parts.
• Remember that HDD is magnetic and CD or DVD is optical.
• Remember tape as sequential and disk as random access.
• Remember that secondary memory is non-volatile.

Common Mistakes to Avoid

• Writing a DVD capacity as 700 MB.
• Mixing the magnetic and optical devices.
• Saying that an SSD has moving parts.
• Mixing CD-R and CD-RW.
• Writing the floppy disk as an optical device.

Quick Revision Points

• Floppy 1.44 MB; CD 700 MB; DVD 4.7 GB; Blu-ray 25 GB.
• HDD is magnetic; CD and DVD are optical; SSD and pen drive are flash based.
• Magnetic tape is sequential access.
• CD-R = write once; CD-RW = rewritable.
• Secondary storage is non-volatile.

Practice Questions With Answers

1. What is the capacity of a CD?
   Answer: 700 MB (Optical disc).
2. What is the capacity of a single-layer DVD?
   Answer: 4.7 GB (Optical disc).
3. Which device uses a blue-violet laser?
   Answer: Blu-ray (25 GB).
4. Which storage has no moving parts?
   Answer: SSD (Flash memory).
5. Which storage is accessed sequentially?
   Answer: Magnetic tape (Backup).
6. CD-RW means?
   Answer: Rewritable CD (Can be erased and rewritten).
7. A hard disk is divided into?
   Answer: Tracks and sectors (Magnetic platters).
8. Which is a magnetic storage device?
   Answer: Hard disk (HDD).
9. Which is a portable flash storage?
   Answer: Pen drive (USB).
10. What is a copy of data kept for safety called?
    Answer: Backup (Data protection).

More Practice Questions With Answers

1. What is a group of the same tracks on all platters called?
   Answer: Cylinder (Hard disk).
2. What does RAID stand for?
   Answer: Redundant Array of Independent Disks (Disk arrays).
3. Which laser does a DVD use?
   Answer: Red laser (650 nm).
4. Which laser does Blu-ray use?
   Answer: Blue-violet laser (405 nm).
5. What are the holes on an optical disc called?
   Answer: Pits (Lands are flat).
6. Which backup copies only the changes since the last backup?
   Answer: Incremental backup (Backup type).
7. What is the capacity of a dual-layer Blu-ray?
   Answer: 50 GB (25 GB per layer).
8. Which storage is best for long-term archives?
   Answer: Magnetic tape (Cheap).
9. What is the time to move the head to a track called?
   Answer: Seek time (HDD).
10. Which storage is shock resistant and has no moving parts?
    Answer: SSD (Flash).
11. How many copies does the 3-2-1 backup rule keep?
    Answer: 3 copies (2 media, 1 offsite).
12. Which card is used in phones and cameras?
    Answer: SD / microSD card (Flash).

How to Practise This Chapter

1. Read the tables once and learn the key facts by heart.
2. Revise the quick revision points the next day.
3. Attempt the practice questions above without looking at the answers.
4. Solve a full SSC CGL Tier 1 mini mock to test your general awareness.
5. Check the previous year papers to see how SSC asks computer questions.

Related Notes and Practice Papers

• Computer Memory Notes
• Computer Hardware Components Notes
• Computer Ports and Connectors Notes
• Computer Knowledge Notes for SSC
• SSC CGL Tier 1 Mini Mock

Explore More SSC Subjects

SSC exams test many subjects, so connect this topic with the related subjects below:

• General Science Notes
• General Awareness Notes
• Quantitative Aptitude Notes
• Reasoning Notes
• Electrical Engineering (SSC JE) Notes
• All SSC subjects and notes

Frequently Asked Questions

What is secondary storage?

Secondary storage is permanent storage such as a hard disk, which keeps the data even when the power is off.

What is the difference between HDD and SSD?

An HDD uses spinning magnetic disks, while an SSD uses flash memory with no moving parts and is faster.

What is the capacity of a CD and a DVD?

A CD holds about 700 MB, and a single-layer DVD holds 4.7 GB.

What is a Blu-ray disc?

A Blu-ray disc is an optical disc that uses a blue-violet laser and holds 25 GB per layer.

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

CD-R can be written only once, while CD-RW can be erased and written again.

What is magnetic tape used for?

Magnetic tape is used to store large amounts of data for backup and archives.

Which is faster, a pen drive or a hard disk?

A hard disk is generally faster than a basic pen drive, but an SSD is faster than both.

What is formatting?

Formatting prepares a disk for storing data by creating the tracks and the sectors.

How many questions come from storage devices in SSC exams?

One or two questions usually come from the storage devices.

What is RAID?

RAID is a technology that joins many hard disks to work as one for higher speed, safety of data or both.

What is the difference between full, incremental and differential backups?

A full backup copies all data, an incremental backup copies only the changes since the last backup, and a differential backup copies the changes since the last full backup.

Why is an SSD faster than an HDD?

An SSD has no moving parts and reads data from flash memory chips electronically, while an HDD has to move a head over a spinning disk.