Chapter 6 – Memory and Data Storage

Key words:

  • MIDI – MIDI is often compared to MP3 but MIDI is of lower quality than MP3 and because the file is so big for MIDI, you would have to decrease the file size by about 90%.
  • MIDI uses 8 bit serial transmission with one start bit/one stop bit, 2 of the bits are for start and stop.
  • MIDI contains 16 channels from 0-15.
  • Advantage of using MIDI over MP3 is when memory size is an issue i.e. storing ring tones/music/notification sounds on device with small amount of memory i.e. mobile phone/tablet.
  • Pitch byte is used to work out what key/note/string has been pressed/strung. For example an electronic piano, the note that you pressed is pre stored by a pitch byte.
  • Velocity byte identifies pressure/how loud a keynote/string should be played.
  • MIDI files are saved as .mid
  • MP3 – MP3 is generally used for music whilst MP4 is used for video.
  • MP3 uses technology called Audio Compression to convert music and other sounds into an MP3 file format.
  • MP3 files uses what is known as a Lossy Format since part of the original file is lost following the compression algorithm. This means that the original can’t be converted back to the original again.

Lossy and Lossless Compression:

Image result for lossy and lossless compression

Compression can be lossy or lossless. Lossless compression means that as the file size iscompressed, the picture quality remains the same – it does not get worse. Also, the file can be decompressed to its original quality. Lossy compression permanently removes data. Some image file formats, like PNG or GIF, use only lossless compression, while others like TIFF and MNG may use either lossless or lossy methods.

Comparison between DRAM, SRAM and RAM:

RAM, SRAM and DRAM table

Activity 6.2 explanation video:

Different types of Memory storage:

  • HDD:
    Probably the most common way to store data on a computer. Data is stored in a digital format on the magnetic surfaces of the disk. Normally each disk will have two surfaces which can be used to store the data.
    Cheaper than SSD. More memory storage units.
    Can be slow very quickly. If the disk is damaged the data can be corrupted and can’t be recovered. Latency when message comes up as ‘please wait’ or ‘not responding’

Image result for hdd

  • SSD:
    SSD’s are arguably better than HDD as it is much faster and they have no moving part and all data is retrieved at the same time. SSD’s use chips instead of disks. The most common type of SSD is with NAND chips.
    Much faster than HDD. Chips effectively produces non – volatile re writable memory. More reliable as they come in box like. The box is very hard to get damaged. Low power consumption.
    Smaller gigabytes storage than 1TB for HDD.

Image result for ssd

  • CD and DVD’s:
    CD’s and DVD’s are described as optical storage devices. Laser light is used to read and write data in the surface of the disk. The data is stored in ‘pits’ and ‘bumps’ on the spiral track. A red laser is used to read and write data.
    DVD’s have a larger storage capacity than CDs because the ‘pit’ size.More data stored on the DVD surface.
    The shorter the wavelength of the laser light the greater storage capacity of the medium.

Image result for cd

  • DVD-RAM:
    DVD-RAM
    Instead of using spiral tracks, DVD-RAM uses concentric tracks, this allows the use of concentric tracks simultaneous read and write operations to take place. They also allow numerous read and write operations (up to 100,000 times) and have great longevity (over 30 years) which makes them ideal for archiving.

Image result for DVD-Ram

Blu-Ray:

Blu-ray
A blue laser is used rather than a red laser, is used to carry out read and write operations; the wavelength of blue light is only 405 nano metre compared to red light which is 605 nano meters.
Blu-ray can store up to five times more data than normal DVD

Blu-ray uses a single 1.1 mm thick poly carbonate disks whereas DVDs use a sandwich of two 0.6 mm thick disks.

Blu-ray uses only one layer which means that it is safe from birefringence (light is refracted into two separate beams causing reading errors). DVD’s tend to have a lot of these errors

Blu-ray disks automatically comes with a secure encryption system which helps to prevent piracy and copyright infringement.

Image result for blu ray disk

How data is calculated:

data