1.1.3 Input, Output And Storage- (b. Magnetic, flash, optical storage)

What is the most common magnetic storage?

Hard Disk Drive (HDD).

How does magnetic storage work?

1. The value of each bit of data (0 or 1) is represented as a positively or negatively charged magnetic particle.

These particles are part of a magnetic disk called the platter.

2. Data could be stored anywhere on the disk, and so to read/write data we first need to find the location on the disk.

3. A magnetic read/write head is used to access the data while the platter spins.

What is the reliability of a HDD?

The HDD has moving parts.

Although the HDD is generally reliable, any device with moving parts will be subject to wear-and-tear.

HDDs can also be damaged by shocks. They are not robust.

What are properties of magnetic storage?

:Low cost- very low cost per unit capacity

economical choice for storing large amounts of data.

High capacity- store a large quantity of data in a compact way.

-a popular choice for archives

Good reliability- reliable and tends to last for a long time

-not robust, and tends to break on impact or during vibrations.

Low speed- needs a high number of moving parts, makes it slow to access

What is a hybrid drive?

Combination of magnetic and solid state storage with both benefits

What is magnetic tape?

Used to be for:

-Audio

-Video

-Software

Now for:

-Some video cameras

What are Hard Disk Drives (HDD)?

HDDs are often used as the main form of secondary storage in a computer system.

HDDs hold the operating system, applications, and user data.

How is a bit stored in optical storage?

a pit(0):

a microscopic hole

or a land(1):

flat surface

How is data accessed in optical storage?

A laser is shone on the disk surface.

If the laser hits a land, it will be reflected into a sensor.

If the laser hits a pit, then it will be reflected elsewhere.

These can be used to represent our 1 and 0.

What are example of optical storage?

Blu ray disk:

-store high definition movies or games.

-around 25 GB

Compact Disk (CD):

-around 700 MB

-cheap to produce

Digital Versatile Disk (DVD):

-games or standard-definition movies

-around 4.7 GB

What are types of optical disc?

-Read-Only Memory (ROM)

-Re-writable (RW)

-Write-Once (R)

What are properties of optical storage?

-Low cost

-Low capacity:

Each disk= small

easy to gain a high capacity of storage by buying multiple disks

-Great reliability:

Ideal for portability(Waterproof, Shockproof)

Low speed:

have to move to find the right bit of data on the disk

What are uses of flash memory?

Secure Digital (SD) cards: extend the capacity of devices such as:

Cameras.

Smartphones.

Tablets.

ROM chips: provides the software needed for the computer to start

Solid State Drives (SSD): form of re-writable flash storage

often used in home computers

What are properties of flash memory?

-Fast access

-Non-volatile

-Robust

-Short lifetime

Explain what is meant by virtual memory?

- Virtual memory is an area of the hard disk drive or solid-state drive used as temporary RAM when RAM is full.

- Currently running programs that aren't needed and data are copied when another task needs control of the processor

- Copied back when needed

How does virtual memory work in detail?

1. Memory can be split into sections called 'pages'.

2. Virtual Memory works by moving these pages

3. between the Random Access Memory (RAM) and the secondary storage.

4. If a page is not being used, then we might want to put it into Virtual Memory.

5. When a page is moved to the HDD and not being used, it is put into a special file called the pagefile.

6. Other processes can then use the memory that we just freed in the RAM.

7. When we want to use a page again, we first need to move it back to the RAM.

8. We do this by swapping the page that we want with one that is already in the RAM.