| How is sound stored ? | Samples are taken from the analog sound signal.
By the ADC, each sample is converted to binary form and stored |
| What is file format and what does it represent? | Three or four letter added to the end of every file that represents
1) What type of data the file contains
2) How the data is stored |
| What are the factors that affect quality of the sounds stored? | Sample rate
Sample size |
| How is sound stored through lossy compression? | The sounds which are inaudible to human ear is removed |
| What is a bitmap? | When images are stored, it is divided into pixels, a pixel is the smallest area of the screen that can be changed
A file that contains the color of each pixel stored as a binary number
Number bits needed to store the color of each pixel depends on the number of colors
2 to the power number of pixels = Number of colors |
| What affects the file size of images? | 1) Number of pixels in the image(resolution)- Higher the resolution, better the picture, bigger the file size
2)Number of colors- More the colors bigger the file size |
| How are images stored through lossy compression? | Color variations that the human eye cannot see are removed, reducing the number of colors therefore reducing the number of bits per pixel hence reducing the file size. |
| How are videos stored? | Each minute of video consists of several frames, each frame is stored as a separate bitmap |
| How does lossless compression work? | Repeating characters are identified
The replaced with a smaller code
A key is added at the end of the file |
| Give two differences between lossy compression and lossless compression | Loss has a greater compression rate( up to 90%)
Unlike lossy no data is lost during compression |
| What are the three type of storage devices? | Primary storage
Secondary storage
Offline storage |
| What are the two primary storage devices of a computer? | RAM( Random Access Memory)
ROM ( Read Only Memory) |
| What are the features of RAM? | RAM is volatile (requires power to maintain stored info)
Data s lost when switched off |
| What are the features of ROM? | It is non-volatile
User cannot modify, delete; READ only |
| What is stored into RAM? | Running programs
Data waiting to be processed
Data waiting to be output |
| What is stored into ROM? | Bootstrap loader: Loads operating system
BIOS (Basic Input Output System)- data needed by the processor to communicate with I/O devices |
| What are the advantages of primary store? | Faster to access |
| What are the advantages of secondary store? | Permanent
Larger capacity |
| What are the advantages of offline store? | Permanent
Larger capacity
Portable |
| What are the two types of RAM? | Dynamic RAM (DRAM)
Static RAM(SRAM) |
| How does a SRAM work? | Data input remains until the user changes or switches off
Each bit is stored using a logic gate called a flip flop which is created using two NAND gates or two NOR gates |
| How does a DRAM work? | Data entered degrades ( is lost ) after a short interval and must be entered( approximately 15 microseconds )
Each bit is stored using a transmitter and capacitor
Capacitor holds the data
Transistor is used to switch between 1 and 0 |
| What are the advantages of SRAM and where is it used? | Faster
Memory cache : Some memory closer to the processor used to improve performance
Registers |
| What are the advantages of DRAM and where is it used? | Cheaper
Uses less power
Larger capacity
RAM in PC |
| What are the two types of secondary storage? | Solid State Drive
Hard Disk Drive |
| What are the three magnetic storage deices ? | Hard disk
Magnetic tape
Floppy disk |
| What is latency ? | Time taken for specific data track to rotate around to the READ-WRITE head |
| What are the two types of SSD? | Flash memory
EEPROM ( Electrically Erasable Programmable ROM) |
| What are the features of Flash memory? | Uses NAND gates
Cheaper
Only one block of data is read or written at a time
Majority use this
Non-Volatile Rewritable Memory |
| What are the features of EEPROM? | NOR gates
Faster
Expensive
Single Byte of data can be read/written at a time |
| What are he advantages of SSD over HDD? | More reliable
No latency therefore faster
Lighter and thinner
Produces less heat and less power |
| What is an offline storage? | Non- volatile storage devices that can be easily disconnected from computer and stored in a different location |
| Give four examples of offline storages | CD/DVD/Blu ray ( Optical Drives)
Pen drive ( solid state)
Portable SSD ( solid state)
DVD - RAM |
| How is data written into an optical device? | 1)A laser is shone onto the surface of the disk, the surface is normally covered with a thin aluminium layer.
2) The laser burns pits into the Aluminium, the surface is then covered with pits and lands representing 1s and 0s ( data is written to a single spiral track) |
| How is data read from an optical device? | The laser is shone onto the surface
The reflected light is captured by a light sensor
The amount of light captured for pits and lands are different
This is used to recognize between 1s and 0s |
| What are dual layer DVDs? | A DVD which has two layers to which data can be written |
| What is birefringence? | A problem caused in dual layer DVDSs due to the reflected light from the second layer |
| Why can READ or WRITE be done one at a time with DVDs | Since it has only one track |
| What are the features of a DVD-RAM? | Concentric tracks therefore possible to READ and WRITE at the same time
Lasts longer than a DVD or a CD
Has two layers of polycarbonate |
| What are the feature of a blue ray ? | Uses blue laser which has a shorter wavelength
Therefore: Smaller pits; Higher pit density; Increases capacity
Has a method of encryption which prevents piracy
Higher transfer rate |
| What are the storage sizes of CD, DVD, Blue Ray | CD- 650MB
DVD- 4.5GB -9GB
Blu Ray- >50GB |
| What are the features of memory sticks( Pen drives)? | Portable
Used for temporary backups to move data from one device to another
Used as security dongle |
| What are SD( Secure Digital) / XD( Extreme digital)? | Used to store data in mobile phones, digital cameras and MP3 players |
| How is data transferred from SD cards to the computer? | 1)Connect the device with the card to the computer using a USB cable
2) Transfer the data using a bluetooth connection between the device and the computer
3) Use a SD card reader |
| Explain why should a SD card be properly disconnected before removal? | NAND gate memories write one block at a time, disconnection ensures that last block of data is safe, if it is not disconnected before removal the file maybe corrupted |
