1. Memory and storage
AS identifies the main hardware components of at least two types of computer.
AS states and discusses the implications of the latest computer technologies.
Note to the teacher (Delete this)
In order to display the video on slide 6, the image must only be displayed on the data projector and not on both the computer screen and the data projector. If you are using a laptop, usually you need to press a combination of keys on the keyboard e.g. <Fn><F5>. The *.mpg file must also be saved in the same folder as the PowerPoint presentation in order to get the hyperlink to work.
Textbook 1.6

2. What you are going to learn
The difference between memory and storage.
The difference between RAM and ROM.
What is cache memory.
Which storage media a PC uses.
How the capacity of storage media is indicated.
How to determine the storage capacity of media on my computer.

3. What is the difference between memory and storage?

4. Many of your questions about computers are about memory and storage
Where are all the programs I have installed, stored?
Why do I lose work when there is a power failure?
What is RAM and why will it help to buy more RAM if my computer is slow?

5. Storage
Where our data and programs are stored even when the computer is switched off.
Hard drives, CDs, DVDs, flash disks, stiffys.

6. Memory
Holds the data and the instructions that the computer is working on right now.
Random Access Memory (RAM) is memory chips which are plugged into the motherboard. The card containing the chips is called a DIMM (Dual Inline Memory Module).

7. What collaboration takes place between memory and storage?
All programs that are being executed, are copied from the storage medium (e.g. the hard disk) to the memory (RAM).
All files (e.g. Word documents) that are being worked on, are copied to the memory.
When you save a document, the copy in the RAM is written back to the storage medium.

8. Comparison: memory and storage
Holds the data and the instructions that the computer is working on right now.
Holds all the data and the instructions that the computer has access to when it needs them.
Determines how many programs can be executed at the same time.
Determines how many programs and data can be stored permanently.
Stores data in electronic format – very fast.
Stores data in magnetic/ optical format – slower.

9. Comparison: memory and storage
Loses contents when power is switched off.
Keeps contents even without electricity.
Capacity is measured in Megabytes – typically 512 MB to 1024 MB (1 GB)
Capacity measured in Gigabytes – typically 40 – 250 GB
Expensive per megabyte.
Cheaper per megabyte
Usually DIMMS on motherboard.
Various forms hard disk, CD, etc.

10. Computers are versatile!
Computers can be used for many different tasks, because any program can be copied from storage to memory and then be processed.
Word processing
Playing games
Financial calculations
Communication

11. What does the storage capacity mean?
Computers store all data and programs as combinations of 0s and 1s. The two digits are called Bits = Binary digit.
The bits are stored as magnetic marks on a hard drive.
In the RAM, the bits are stored in small ‘switches’ that are being switched on or off by electricity.

12. What does the storage capacity mean?
Eight bits are needed to represent 1 character (e.g. the letter ‘A’.)
A group of 8 bits is called a byte.
1 Byte

13. What does the storage capacity mean?
Larger units are needed when we store data on a computer. You will not indicate the distance from Jhb to Durban in centimetres but rather in kilometre – similarly you would rather indicate the storage capacity of a hard drive in gigabytes than in bytes.

14. What does the storage capacity mean?
Unit
Abbrevia-tion
Number of bytes
1 kilobyte KB
1024
1 megabyte MB
1024 KB
= 1024 x 1024
= bytes
1 gigabyte GB
1024 MB
= 1024 x bytes
1 terabyte TB
1024 GB
= 1024 x 1024 x 1024 x 1024 bytes

15. RAM and ROM

16. How does the computer work when memory is lost without electricity?
Computers need a program to tell them what to do.
A program can not be executed if it is not loaded in the memory.
Memory doesn’t have any instructions when the computer is switched off.
Where does the computer then get its instructions from when it is switched on?

17. Special memory - ROM
All instructions (programs) that are needed to start the computer, are stored in the Read Only Memory (ROM).
These programs are stored on a micro chip that is mounted on the motherboard.
The programs remain on the ROM, even when there is no power.
One of the tasks of the programs is to load the operating system in the RAM – the operating system then controls the computer.

18. Why is RAM important?
RAM is fast – therefore you want to be able to store all the progams that you work on, in RAM.
The more RAM you have, the more programs and data can simultaneously be in the RAM and the faster the programs will run.

19. How much memory must a computer have?
Determined by the type of applications used.
Graphics, games, film editing – up to 1 GB; ‘normal’ applications 512 MB.
Look at the specifications of new software – it usually indicates the minimum amount of RAM needed.

20. Do Activity 1

21. Cache memory Special high speed memory
Various parts of the computer – including the CPU
Comparatively small (measured in KB)
Stores work that the CPU is most likely going to use next.

22. Memory specifications
Number of pins that make contact with slots.
Capacity
Type of memory: Double Data Rate
240 pin DIMM 512MB DDR2 (PC667)
ECC Registered.
Speed of the memory in MHz
Error Correction Code
Reduces electricity consumption.

23. Do Activity 2

24. Storage

26. Disk terminology

27. Disk terminology
Formatting: Makes marks on the disk to define the tracks and sectors.
Partition: Dividing one hard disk in two parts that can then be handled as two different disks.
File system: The format in which files and information is stored. Win XP uses the NTFS file system.

28. Disk terminology
File Allocation Table (FAT) : A table in which record of all the files that are on the disk, is kept as well as in which clusters they are and whether there are any ‘bad sectors’ that can’t be used.

29. Hard disk
Hard drive controller
Disks or platters
Read/write heads

30. Hard drive specifications
the capacity of the hard disk, measured in gigabytes (GB)
the speed at which it rotates, measured in revolutions per minute (RPM) and
the interface which connects it to the computer

31. Do Activity 3

32. Portable storage devices and media
Portable hard drives
Portable flash drives
flash drives with integrated MP3-players, radios and voice recorders
flash drives to boot your computer
flash drives with built-in functions to read finger prints and do encryption to keep your data safe and secure.

33. Do Activity 4

34. Other magnetic media
Digital tape drivers – used to make backups of large quantities of data, like these on a network.

35. Optical media Makes use of laser beams to read and write data.
1 CD ROM = 450 stiffies
From 650 – 750 MB.
Software usually installed from a CD.

36. CD (Compact Disc) CD-ROM Writing to a CD = burning of a CD CD formats
CD Read Only Memory. Manufacturer writes once. Can’t be erased or rewritten– e.g. music or software CDs.
CD-R
CD-Recordable. Can be written to several times in multiple sessions. Can’t erase when the disc is full. Home use.
CD-RW
CD-ReWritable. Can be written to until disc is full, then erased an rewritten to.

37. Do Activity 5

38. DVD Digital Versatile Disc (also called Digital Video Disc).
4.7 GB up to 17 GB
DVD-R : recordable
DVD-RW : re-recordable
DVD-RAM disks: can be written and erased repeatedly, but they are only compatible with devices that support DVD-RAM format.

39. DVD
Dual sided & Dual layer: Can be written on both sides an in two layers.
Blu-ray and HD-DVD – capacity of 50 MB and 100 MB.

40. Why is DVD better than CD?
Larger storage capacity and increased speed in comparison with CDs.
Backup of a hard disk can be made on DVDs.
The decrease in prices of writable DVD media and DVD-writers makes it a viable alternative for CDs.

41. What next?
Storage must increasingly have bigger capacity because of the growth in storing of music and films.
Storage must be portable so that data can be transferred to other devices.

42. Do Activity 6
Do Activity 7
Do Activity 8
Do Activity 9