Summary

SUMMARISE

  -   Permanent: Data is protected from any alterations.

  -   Sequential access: Storage locations have to be read or written in their correct order starting with the first location.

  -   Random access: Storage location can be directly read or written. Also called ‘direct access’.

        Primary Storage

-   Onboard storage devices built into an information system (e.g. motherboard)

-   Fast, easy to use and accessible at any time

-   Random access memory ( RAM)

·      Found on BIOS.

·      Checks system and loads the operating system.

·      Designed for temporary use only

·      As soon as power is turned off, all contents of RAM are erased.

·      Random

·      Volatile because it needs constant power supply to keep its data.

-   Read only memory ( ROM)

·      Random

·      Not volatile’

·      Permanent [ ROM & PROM only ]. Only permanent MEMORY STORAGE DEVICES. 

Secondary Storage

-   Storage devices attached to an information system

-   More permanent.

-   Provides space for data and software that are not immediately needed by the information system.

-   Hard disks, Floppy discs, CDs.

-   CD

·      Random

·      Not volatile

·      CD Rom, CD- A, CD-R are non recordable DVD.

Volatile

-   Refers to storage decives that will lose all their data if the power is switched off.

  Non-Volatile

-   Opposite

             CPU

-   Wider data bus: Consisting of wires that allow data ti enter and leave the CPU. It controls the number of data bytes that can enter and leave the CPU in a single step.

E.G. one with 64 bits can more 8 bytes of data in or out in one operation.

- Faster clock speed: CPU that operates with a clock speed of 2GHz will obey twice as many instructions in a second as a CPU with a clock speed of 1GHz.c

-  Higher FLOP rating. ( Floating-point Operation ) indicates how many floating point number can be added together in a second. It is considered to be more reliable indicator of CPU speed than clock speed.

- Is working in parallel with other CPUs. If the information system contains multiple CPUs then it may be possible to divide the analysing process between them so that each CPU gets a shorter list of task to perform. 

Motherboard

-   Central printed circuit board in many modern computers which holds many of the crucical components of the system, while providing connectors for other peripherals.

-   Also known as the main board, system board.

-   Include:

·      sockets

·      chipset

·      non-volatile memory

·      clock generator

·      slots for expansion cards

·      power connectors.

DISPLAYS –CRT, LCD

       CRT ( Cathode Ray Tube)

-   Sealed vacuum tube that can fire and accurately focus beams of electrons on a chemically coated screen.

-   Problems

·      Bulky and heavy

·      Uses a lot of electricity

·      Scan line refresh tech. can produce noticeable flicker.

-   Its alright: manufacture, produces bright, clear display, viewed from all angles

LCD ( Liquid Crystal Display)

-   Uses a material that switches between blocking light and allowing it to pass through when an electric current is applied.

-   LIKE CRT organised into pixels, each containing group of three crystals. 

Activities pg 145

nREMEMBER
1. Random Access: That any storage location can be directly read or written.
* It is also called "direct access"
 Storage device:
-DVD
-USB Memory Device
-Hard Disk Drives
2.Sequential Access: That any storage locations have to be read or written in their correct order, starting with the first location.
Storage Device:
- Tape
3. Volatile: Storage devices that will lose all their data is the power is switched off.
- RAM not volatile

THINK
4. RAM is the only volatile storage device as it needs a constant power supply to keep its data.
- Refreshed

- SSD ( Sold State Drives): Instead of using hard disk drive, they use flash memory. They are secondary storage, form role of hard disk, but use flash memory. They are not removable
Advantages:
- Fast
- No moving parts, thereby don't tend to crash.
- No motor to fail
- No read write head to crash

- How long can they last?
- Solid State Drive: Like having memory sticks within the computer.
- Solid State Drive good for cameras, due to the environment cameras are used in.

* Hard Disk Drive: Motor which spins the disk, 7000 revolutions/minute. Floating above it, delicate wafer, devices that can magnetic fields and generate magnetic field. Disk has ion compound and can be ionised. Can read magnetic patterns of disk.
* Read write head, crashes onto the surface: it destroys the surface, regions on the disk that are corrupt. Not hard to corrupt hard disk.
5. Sequential access devices are better suited for storing backup data due to [its speed problem.]
Note: It is the slowest, especially if data is at the other end of the tape.
- there are tape systems which record the position of every file on the tape.
- it then uses fast forward and fast rewind to move quickly to the file.
- in saying this their speed is significantly slower than disk access.
Therefore better suited for storing back up data as well as long term data storage.

Activities pg 141

REMEMBER
1. The most common type of RAM used in computers are:
- SDRAM ( Synchronous)
2. EE ( electronically erasable) EEPROM is the most useful of the ROM type of memories as:
- data can be erased by exposing the chip to ultraviolet light.
- new data can be added
3. Optical storage devices store data as light- false

THINK
4. PROM would be an ideal storage device for security data as:
- prevents any alteration of the data
- once the data is added it cannot be changed.
5. Examples of situations where CD-R is a better choice for data storage than CD-RW is:
- For archiving, CD-R will be a better choice/
Note:
-->CD-R ( CD Recordable) technology uses a coloured dye that can be changed by heating to permanently record data.
--> CD-RW ( CD- ReWriteable) technology uses a dye that can be switched betweeen cloudy and transparent.

6. 3.5 inch floppy disks have changed very little since they were first introduced in the mid 1980's- that makes them old technololggy.
 Reasons for their continued popularity include:
- they are still partially compatiable
-" higher density drives are built to read, write and format lower density media without problems, provided the correct media is used."

RESPOND using assess
7. The advantages and disadvantages of flash storage devicesd as replacements for floppy devices are as follows:
Advantages- Flash memory storage devices
- fast and do not require any power to keep data in storage.
- smaller, more compact
- capacity- much bigger
- once data is written into the chip by applying an electric charge to each memory location, its electric charge is trapped and does not need any electric power to be kept there.
- no moving parts, thereby there is no issue of significant danger being done to wipe out or corrupt data in any way.
Advantages- Flash RAM
- uses less power but requires a small electric curren to remember its stored data.
- better suited for small, low power portable devices.
Diadvantages
- higher cost
- contents of an entire flash memory chip can be erased in a single operation.

MAGNETIC FIELDS
- Magnetic
- If on floppy disk, contents can get deleted.