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Computer Components: Storage Devices (Types of memory The two main types…
Computer Components: Storage Devices
Types of memory
The two main types of memory used in computers are:
RAM
ROM
RAM
R
andom
A
ccess
M
emory
What is often stored in it?
Operating System
Running Programs
Data currently being used
What happens to its contents when you turn the power off?
They are lost.
This type of memory is volatile.
Can you read and write data to it?
Read & Write
Access to RAM is very fast.
The computer stores running programs and data in RAM when your computer is turned on.
When your computer is off, RAM is empty as it is volatile.
-
All your programs and data are safe on your hard disk.
1.
When you switch on your computer,the startup instructions load the operating system from your hard disk into RAM.
2.
When applications or programs are loaded,they are copied into RAM from secondary storage. (e.g. hard disk)
Documents (data) that are used with those programs are also opened by copying them into RAM as the working memory.
3.
RAM starts to fill up.
Running out of space
You now want to open a browser to search the Internet.
The browser software needs more memory than you have free in RAM.
Virtual Memory
Virtual memory is part of the hard drive used as an extension to RAM.
ROM
R
ead
O
nly
M
emory
What is often stored in it?
Computing bootup instructions (Bootstrap).
What happens to its contents when you turn the power off?
They are retained. This type of memory is Non-Volatile.
(Some data needs to be permanently held in memory, even when a computer has no power)
Can you read and write data to it?
Read only
Primary and Secondary storage
Primary storage is volatile and usually refers to RAM.
Secondary storage refers to non-volatile storage:
-
Magnetic storage such as the hard disk.
-
Optical storage that uses laser light such as CD-ROM.
-
Solid state devices using flash memory.
Cloud storage
Secondary storage devices
Different technologies have evolved for saving data.
Each of these have their own advantages and disadvantages in terms of:
-
Durability
-
Read / write speed
-
Capacity
-
Portability
-
Cost
Inside a hard disk
Tracks, sectors and platters
-
Concentric tracks are created on a magnetic disk.
-
Disk spins at high speed: 3,600 - 7,200rpm
-
Spinning platters are each read by drive heads.
Data is read or written as sector moves under the head.
Company server data
Hard disks have very high capacity.
-
Fast read and write speeds.
-
Relatively cheap storage per TB.
Solid State Drives
Solid state media commonly uses electrically programmable non-volatile
flash memory
.
Advantages
More durable
-
SSD cards have no moving parts so can survive drops, extreme heat and cold, and extreme pressure.
Faster than hard disk drives.
Consume less power.
More portable.
Disadvantages
Typically less capacity than a hard disk.
More expensive than hard disk drives.
USB flash drives
-
Can store up to 128GB of data; that's 2,500 photos.
-
Prices start under 5.00
-
Can use password protection.
-
Useful for transferring data between computers.
CDs, DVDs and Blu Ray
Why are the capacities of these discs different given they are all the same physical size?
Different laser wavelengths 'burn' smaller pits.
The spiral track can therefore be more tightly wound, creating a longer track.
Optical disk formats
Optical disks are available as:
-
Read only
-
Recordable
-
Re-writable
Software mailing
-
Often best suited to optical disks.
-
Cheap to manufacture and distribute.
-
Robust during carriage.
-
Lightweight.
CD formats
CD
s come in three different formats:
-
CD-ROM (Read only)
-
CD-R (Recordable)
-
CD-RW (Rewritable)
CD-ROM
is "pressed" at the time of manufacture.
CD-R
can be written to once.
CD-RW
can be written, read many times, erased and written again.
Uses for optical disks
CD-ROM
is widely used for software distribution.
CD-R
may be used for copying a game, software, audio or video files or documents. These can then easily be stored offline.
CD-RW
useful for short or medium term back-up, or transferring files from one computer to another.
DVD
and
BluRay
are high capacity discs which can store feature lengths films.
Capacity and access speed
The development of solid state media is moving very quickly and set to replace traditional hard drives in most instances.
