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Data Storage Cheat Sheet

A Education › Science cheat sheet in English by Rachit Murarka

Notes for IGSCE Hardware chapter for the subject Computer Science(0478)

Science Storage Data Systems Computer 3 Hardware IGCSE
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Memory and Storage devices

Category
Devices
Primary Memory
RAM, ROM, Cache Memory
Internal Secondary Storage
Hard Disk Drive (HDD), Solid State Drive (SSD)
External Secondary Storage
DVD/CD, DVD-RAM, Blu-ray Disc, USB Memory Stick/­Flash Memory, Removable Hard Drive

Comparison of RAM and ROM

Feature
RAM
ROM
Type of Memory
Temporary memory
Permanent memory
Volatility
Volatile (contents lost when powered off)
Non-vo­latile (contents retained)
Read/Write
Can be written to and read from
Data stored cannot be altered
Usage
Stores data, files, part of an applic­ation or OS
Always used to store BIOS and other data

Virtual Memory vs. Normal Memory Management

Feature
Virtual Memory
Normal Memory Management
RAM Utiliz­ation
Programs larger than physical memory can be executed
Limited by the available physical memory
Data Movement
Data moved in and out of HDD/SSD as needed
No movement of data between memory and storage
Disk Thrashing
Can lead to disk thrashing if not managed properly
No disk thrashing as data stays in RAM

DRAM(D­ynamic RAM)

Aspect
Descri­ption
Compos­ition
Consists of transi­stors and capacitors
Operation
Capacitor holds bits of inform­ation (0 or 1); transistor acts as a switch for readin­g/w­riting
Refresh
Requires constant refreshing (every 15 micros­econds) to prevent data loss

Magnetic Storage (Hard Disk Drives - HDD)

Aspect
Descri­ption
Data Storage
Data is stored in a digital format on the magnetic surfaces of disks (platters) with read-write heads
Latency
Slower data access compared to RAM; latency occurs as the read-write heads search for the correct data
Fragme­ntation
Fragme­ntation occurs over time, affecting perfor­mance; defrag­men­tation software can improve this

Memory Sticks­/Flash Memory

Uses solid-­state techno­logy; small, lightw­eight devices suitable for transf­erring files between computers

Virtual Memory

Aspect
Descri­ption
Purpose
Extends physical RAM, allowing larger programs to run; utilizes hard disk or SSD as swap space
Paging
Uses paging to store and retrieve data from HDD/SSD, copying it into RAM
Advantages
- Programs can be larger than physical memory
- Reduces the need for expensive RAM

Blu-ray Discs vs DVDs

Aspect
Blu-ray
DVDs
Laser Color
Blue
Red
Wavelength of Laser Light
405 nm
650 nm
Storage Capacity (Dual-­Layer)
Up to 50 GB
8.5 GB (for dual-layer DVDs)
Intera­ctivity
Greater intera­cti­vity; high definition movies
Limited intera­cti­vity; standard definition movies
Data Transfer Rate
36 Mbps
10 Mbps

Primary and Secondary Storage

Storage Type
Storage Type
Primary Memory
Directly addres­sable by CPU, contains RAM, ROM, and cache memory
Secondary Storage
Not directly addres­sable by CPU, non-vo­latile devices (e.g., HDD, SSD, DVD)

Comparison of DRAM and SRAM

Feature
DRAM
SRAM
Constr­uction
Transi­stors and capacitors
Flip flops
Refresh Requir­ement
Needs constant refreshing
No constant refreshing
Cost
Less expensive
More expensive
Power Consumtion
Consumes less power
Consumes more power
Memory Capacity
Higher memory capacity
Lower memory capacity

Types of Optical Storage Media

Media Type
Charac­ter­istics
CD/DVD
Uses laser light to read and write data on metal alloy or organic dye layer
Blu-ray
Uses blue laser light, smaller pits and lands, higher capacity, and dual-l­ayering

Cloud Storage Benefits and Drawbacks

Aspect
Benefits
Drawbacks
Data Redundancy
Increased data redundancy and access­ibility
Security concerns and potential data loss
Access­ibility
Access data from anywhere with an internet connection
Relinq­uishing control over data security
Cost
Cost-e­ffe­ctive storage solutions
Risk of data loss from hacking and security breaches

SRAM(S­tatic RAM)

Aspect
Descri­ption
Compos­ition
Uses flip-flops to hold each bit of memory
Refresh
No constant refreshing needed
Speed
Faster data access compared to DRAM (typic­ally, access time for SRAM is 25 ns)

SSD(Solid State Drive)

Aspect
Descri­ption
Compos­ition
Uses NAND or NOR chips to control the movement of electrons, storing data as 0s and 1s in transi­stors
Advantages
- More reliable (no moving parts)
- Lighter and suitable for laptops
- Faster data access than HDD

Virtual Memory

Aspect
Descri­ption
Purpose
Extends physical RAM, allowing larger programs to run; utilizes hard disk or SSD as swap space
Paging
Uses paging to store and retrieve data from HDD/SSD, copying it into RAM
Advantages
- Programs can be larger than physical memory
- Reduces the need for expensive RAM

Cloud Storage

Aspect
Descri­ption
Types
-Public cloud (different provider and client companies)
-Private cloud (integ­rated client and provider)
-Hybrid cloud (combi­nation of public and private)
Reduncy
Data redundancy on multiple servers to ensure availa­bility
Security Risks
Risks include physical security, natural disasters, and potential data loss from hacking or other breaches

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