Understanding Computer Storage: From ROM and RAM to External Drives
Computer Storage: An Overview
A computer utilizes two primary types of storage: main storage and backing storage. Main storage comprises ROM and RAM, while backing storage can be internal, such as a hard disk, or external, like a CD or USB flash drive.
ROM and RAM
ROM (Read-Only Memory)
ROM is non-volatile memory that persists even when the computer is powered off. It stores essential instructions, such as the computer’s startup routine. Neither programs nor users can modify ROM content.
RAM (Random Access Memory)
RAM is volatile memory used for temporarily storing programs, applications, and data actively used by the computer. Examples of data stored in RAM include:
- Operating system
- Applications
- Graphical User Interface (GUI)
RAM’s contents are erased when the computer loses power.
Storage Capacity and File Size
Storage capacities and file sizes are measured in increasing order:
- Bits
- Bytes
- Kilobytes
- Megabytes
- Gigabytes
- Terabytes
Operating systems typically abbreviate these units, such as 1MB for 1 megabyte.
Relationship Between Measurements
The table below illustrates the relationship between the smallest unit (bit) and the largest (terabyte):
| Size | Equal to |
|---|---|
| 8 bits | 1 byte |
| 1024 bytes | 1 kilobyte |
| 1024 kilobytes | 1 megabyte |
| 1024 megabytes | 1 gigabyte |
| 1024 gigabytes | 1 terabyte |
File sizes and storage capacities are always expressed in their simplest form. For instance, a 1 terabyte hard disk is denoted as 1TB, not 1024GB.
Example File Sizes (Compressed)
| File | File Size |
|---|---|
| Photo | 3MB |
| Song | 5MB |
| Film | 700MB |
File size depends on the amount of information stored; larger files contain more data.
Internal Backing Store: The Hard Disk
The primary internal backing store is the hard disk, responsible for storing:
- Operating system
- Software applications or programs
- The majority of user data files
Hard disks are high-speed storage devices (around 7,200 RPM) housed within the computer. They offer substantial storage capacity, typically ranging from 200GB to 1TB or more in desktop computers. Data on a hard disk is retained until deleted but needs to be loaded into RAM for processing.
Floppy and Zip Disks
Floppy disks, with a limited capacity of 1.44MB, require a floppy drive for reading. They are used for:
- Transferring small files
- Backing up small, important files
- Storing restricted files
Zip disks resemble larger floppy disks, offering 250MB or more of storage. They require a zip drive and serve similar purposes as floppy disks. Newer storage media like DVD-RWs and memory sticks have largely replaced floppy and zip disks.
External Backing Stores: Optical Discs
CD (Compact Disc)
CDs, based on the same technology as music CDs, can store up to 700MB of data. They are suitable for multimedia applications, pictures, sounds, video clips, and more. CD formats include:
- CD-ROMs: Read-only, data is pre-written.
- CD-Rs: Recordable, allowing one-time or multi-session writing.
- CD-RWs: ReWritable, enabling multiple write and rewrite cycles.
DVD (Digital Versatile Disc)
DVDs, physically similar to CDs, offer significantly higher storage capacity, with single-sided discs holding up to 4.7GB. Commonly used for video storage, their capacity is often measured in minutes (e.g., 4.7GB = 120 minutes). DVD formats include:
- DVD-ROMs: Read-only, data is pre-written.
- DVD-Rs: Recordable, allowing one-time or multi-session writing.
- DVD-RWs: ReWritable, enabling multiple write and rewrite cycles.
CD/DVD Drives
CD/DVD drives facilitate reading and writing data to CDs and DVDs. Modern drives typically support all CD and DVD formats, including CD-R, CD-RW, DVD-R, and DVD-RW. Data transfer is accomplished using a laser.
Other External Backing Stores
Magnetic Tape
Primarily used for backing up crucial files from the hard disk and long-term data storage and archiving.
Advantage
- Compact, durable, portable, and cost-effective per GB.
Disadvantages
- Slow write and read speeds.
- Serial access, requiring reading the entire tape to access specific data.
External Hard Disks
External hard disks provide extensive storage capacity (e.g., 1TB or more) and connect to computers via USB or FireWire ports. They function similarly to internal hard disks but are housed in external casings.
Advantage
- High capacity, suitable for backups and transferring large data volumes.
Disadvantages
- Often bulky and less portable.
- Susceptible to damage from drops due to moving parts.
Memory Sticks
Memory sticks are compact, pen-drive-sized USB devices that function similarly to floppy disks but connect to USB ports. They offer storage capacities ranging from 512MB to 32GB and beyond.
Advantages
- High storage capacity.
- Highly portable.
- Durable due to no moving parts.
Disadvantage
- Increased risk of loss, theft, or damage due to portability.
Data Backup and Archiving
Importance of Backups
Data backups are crucial for various reasons:
- Accidental file deletion
- Hard disk failures
- Data loss due to viruses
- Data protection against physical damage (e.g., fire)
Data loss can have severe consequences, especially for businesses. Regular backups are essential to mitigate these risks.
Backup Frequency
The frequency of backups depends on the data’s value and how often it changes. Valuable data and frequently modified data require more frequent backups.
Archiving
Archiving involves moving infrequently used but potentially valuable data to dedicated storage media (e.g., DVDs or magnetic tape) for long-term preservation. This frees up space on the primary storage system.
Computer Viruses
What is a Virus?
A virus is a malicious program designed to harm computer systems. It spreads by replicating itself and attaching to other files. The severity of damage varies depending on the virus.
How Viruses Spread
Viruses are primarily spread through email attachments, illegal software downloads, and infected files from the internet. Up-to-date antivirus software can detect and mitigate these threats.
Preventing Virus Infections
Sensible precautions can significantly reduce the risk of virus infections:
- Keep your operating system and antivirus software updated.
- Exercise caution when opening email attachments from unknown sources.
- Avoid using memory sticks from untrusted sources.
- Download files only from reputable websites.
- Refrain from using software from unreliable sources.
Antivirus Software
Antivirus software scans computer files and email attachments for viruses, removing or quarantining any detected threats. Regular data backups are crucial for restoring data in case of a virus attack.
Types of Viruses
Worms
Worms are self-replicating programs that spread through computer networks, consuming system memory and bandwidth.
Trojan Viruses
: A Trojan virus is one that opens your computer up to malicious users allowing them to read your files.
VIRUSES:“A virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes.”
Difference Between a Virus, Worm and Trojan Horse:
•Virus cannot replicate themselves but worm and trojan can do that.
•A virus cannot be spread without a human action such as running an infected file or program but worm and trojan have the capabilities to spread themselves automatically from computer to computer through network connetion.
•A virus do not consume system memory but worm consumes too much system memory and network bandwidth because of their copying nature.
•Trojans are used by malicious users to access your computer information but viruses and worms can’t do so, they simply infect your computer.