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Unit 1: 1.2 cont'd - Storage and Memory
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1.2 cont'd - Storage and Memory
Revise, Recap, Review
Write your question on the front and the answer on the back, then stick to the board
Green = Easy
Yellow = Hard
Objectives
Lesson Objectives
To understand the difference between primary and secondary storage
To understand the purpose and use of optical storage and magnetic tape
To understand the necessity of ROM in the computer system
Storage
Three tiers of storage that we will talk about today:
Primary
Secondary
Tertiary
Theory
Primary
Refers to the fastest available storage
- Registers in the CPU
- Cache
- RAM
- ROM
Primary storage is usually volatile
Which example above is NOT volatile?
Primary
The CPU fetches data and instructions from memory to process.
The CPU can't directly access files from storage, only memory.
Accessing files from the hard drive would be too slow!
The two main types of primary memory are
RAM and ROM.
RAM
Can be accessed at any time
Data copied from storage to RAM
RAM temporarily holds the programs and data currently in use - inc OS
Volatile
Data stored as an electronic charge - needs to be topped up!
Question
If you are listening to some music while researching on the internet for information to use in a word processed document, what might be contained in RAM?
- The operating system for the computer
- Music player software
- The music file you are listening to
- The web browser software
- The website you are looking at
- The word processor software
- The word-processed file
- Anti-virus software
ROM
We already know that ram can only work when the computer is turned on, and the CPU can't directly access files on the HD...........so how does the OS get into ram so that the CPU can access it?
ROM
ROM is a more complex electronic circuit that is non-volatile.
Information in the ROM is placed on the chip by the manufacturer, and often contains the boot program - firmware
This Program:
Performs some basic system checks
Finds the OS and tells and loads it into RAM
Hands over control to the OS
Secondary Storage
Secondary storage is non-volatile
Used to store data (OS, files and applications) that are not in use.
Magnetic disks, SSD, CD's and SD (secure digital) cards
Read/Write speeds are MUCH slower than primary storage.
Magnetic Disks
Common form of internal (and external) storage in PC's and laptops
Stack of magnetised disks (platter's) that spin between 5-15k RPM
Platter divided into billions of tiny areas called sectors
Read/Write head moves over the sector and changes the state of the sector to store a binary bit.
Hard drives have a movable arm with a read/write head attached to the end of it.
This moves over the spinning platter to access sectors in data tracks.
Despite these moving parts, hard drives are fairly reliable but can be damaged if dropped
Solid State Drives
No moving parts
Use Flash memory
Binary data stored as an electrical charge
Faster than HDD
More expensive per GB
Hybrid drives *
Hybrid drives exist that combine traditional magnetic storage with flash storage for use by OS and programs
Other solid storage
USB pen drives
Memory cards
- Much slower than SSD drives
-Lifespan is significantly shorter
Primary use is to expand storage or provide portability
Task
Media vs Device
Be careful with your terminology!
Storage media = What the data is held on, E.G. optical disc, magnetic tape etc.
Storage device = The device that reads/writes the data, E.G. HDD, SSD, DVD drive etc.
Optical Storage
CD's, DVD's Blu-ray
700MB, 4.7GB, 25GB
Work by burning pits into the shiny surface of the disc with a laser
Most modern devices don't come with disc drives anymore....
+ Cheap
+ Water resistant
+ shock resistant
+ Portable
- Scratched easily
- Slow
- Small capacity
- Poor reliability
Cloud Storage
The Cloud
Cloud storage isn't really in the clouds
Internet connection used to access storage array connected to server - somewhere, anywhere!
Paid for service - pay as you go
+easy to expand
+use only what you need
+no backups
-who owns the data
-internet connection req.
-security risks
Tertiary
Archiving/backups
Huge capacity and cheap
Used to store large quantities of data - school
Plastic cassettes hold long reels of magnetic tape
Special drive used to read/write data
Data read/written sequentially - start to finish
- slow to find specific data
Shared:\Computing - ICT\KS5 - CamTech Level 3\LO1\1.2
Now create a set of flashcards to help you prepare for the exam
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