4.6 Memory/4.7 Secondary storage

Types of Main Memory

RAM, ROM

What is RAM used for

Temporary storage of programs currently being executed and the data the programs are using

Can processors access secondary storage

No they have to be loaded into main memory

Main Memory

All memory that is directly accessible by the CPU

Secondary Storage

Non-volatile storage not directly accessible by the CPU

What does RAM usually store

The OS, currently used software, data software uses

How is RAM volatile

When the power is turned off all the data is lost

What does ROM usually store

Bootstrap, Basic Input/Output System (BIOS)

What is a bootstrap

A program that loads the OS

Memory Speed

The speed that data can be accessed

Types of secondary storage

Hard Disk Drives (HDDs), optical disks, Solid State Drives (SSDs)

Benefits of secondary storage

Non-volatile, holds much more data than main memory, inexpensive per MB

Disadvantage of secondary storage

Slower access speeds

5 features to consider about storage devices

Capacity, speed, portability, durability, reliability

Magnetic storage

A type of secondary storage that uses magnetic patterns to store data on a rotating disk

How are magnetic disks read/written to

Read/write heads move across the surface of the discs which are rotating at a very high speed. A whole sector is read in one go

How do HDDs look

HDDs contain multiple platters (discs) which are organised in concentric rings (tracks) that’s divided into sectors

How is binary represented on a magnetic disk

Iron particles are polarised to become north or south state. One direction is 0 and the other is 1

Hard disk

Has a solid platter

Floppy disk

Has a soft plastic platter

Advantages of magnetic disks

Huge capacity, cheap

Disadvantages of magnetic disks

Slower to access and susceptible to damage (due to many moving parts), vulnerable to magnetic fields, not portable

Fixed/internal hard disks

Large storage capacity used inside PCs

Portable hard disks

Connects to computers via USB port

Examples of magnetic storage

HDDs

Solid State Storage (SSD/flash memory)

A type of secondary storage that uses electrical circuits to store data

Example of solid state devices

Memory sticks, memory cards

How do SDDs work

A large electrical current forces electrons through a barrier and traps them on the other side

Advantages of SDDs

Very high access speeds, portable (small), durable (no moving parts), doesn’t need defragmenting

Disadvantages of SDDs

Expensive per GB, lower capacity

Optical Storage

A type of secondary storage that uses lasers to read and write data on rotating discs

Examples of Optical storage devices

CDs, DVDs, Blu-ray discs

How is data stored on an optical disk

Data is stored as pits and lands that are burnt or pressed into a single spiral track

How is data read from an optical disk

A laser head moves across the disk and the laser passes over the pits and lands. The level of reflection is measured (as light reflects less well where pits start/end) and interpreted into binary

Advantages of optical disks

Small and lightweight (portable), cheap per disk

Disadvantages of optical disks

Low capacity, slow access speeds, easily scratched/damaged

Cloud storage

Storing digital data on remote servers accessible over a network rather than directly on the user’s device

What type of storage to cloud services use

Magnetic, solid state

How is data commonly accessed from the cloud

Via the internet

How do third party cloud managers protect user data/ be more reliable

Make multiple copies of the data so if one server is damaged it can be accessed by another

Who controls data backups with cloud storage

The cloud provider

Why is cloud storage commonly used in businesses

It makes sharing data/files easier with people in different locations

4 Advantages of Cloud Storage

Easy to use, high potential storage capacity, convenient as it can be accessed anywhere, reduces need for secondary storage

4 Disadvantages of cloud storage

Can’t be accessed without internet connection, data privacy issues, relies on access to high bandwidth network connection, could cost more long term

Why is cloud storage being used more often

High level of trust, higher bandwidth mobile networks, increased availability of mobile devices, improvements in network security

Volatile

A type of memory whose contents are lost when the computer loses power

What are HDDs used for

Desktop PCs, servers

What are SSDs used for

Laptops, phones, tablets

What are optical disks used for

Sharing and distributing small volumes of data