Chapter 6 Memory and Data Storage

Introduction:

There many different types file formats which are used to store data, it can be text, sound and images. All computers systems have primary memory and secondary memory storage.  Computers can store information into different file formats. The most common are:

File Formats:

There are many different file formats such as:

  • JPEG
  • MP3
  • MP4
  • MIDI (Musical Instrument Digital Interface)
  • Different sounds, texts and numbers format

Keywords:

  • MIDI
  • Velocity byte
  • Pitch byte
  • Velocity byte
  • asynchronous
  • serial transmission
  • File compression
  • Bit rate
  • MPEG
  • JPG
  • BMP
  • PNG
  • TIF
  • Embedded Computer:  A computer that is built for specialized tasks.
  • General Purpose Computer: A computer used for many different applications.

Musical Instrument Digital Interface (MIDI):

MIDI is a type of a file format which allows storage for music. MIDI files usually compresses the music files, which means the quality is lower than MP3 files. They are usually compressed by 90%. The reason normal people don’t realize the difference is because it gets rid of the sound the ear cant hear and if one tone is higher than the other, the lower tone gets deducted.  MIDI uses 8-bit serial transmission (one bit at a time, over a single wire/channel), which is therefore asynchronous (not occurring at the same time).MIDI contains 16 channels from 0-15.  The pitch byte in MIDI detects the key/note/string and how it has been stung/pressed. The velocity byte detects pressure/how loud a keynote/string should be played. MIDI files are saved in .mid.

MPEG-3 (MP3) and MPEG-4 (MP4):

MPEG-3 (MP3) are music files. They use audio compression making music in MP3 format.  They reduce the file size by 90%.  The CD files use file compression, and the music is usually at satisfactory level.  MP3 files use a a format called lossy format which means that during the reduction, some parts of the files are lost so they cant be put back together.  The quality can differ due to the bits per second, usually 200 or more gives you a satisfactory level of sound, which is similar to to CD’s.

MPEG-4 (MP4) are used for multimedia, such as: videos, animations, music, photos etc. MP4 can be streamed over the internet without losing any real discernable quality.

Joint Photographic Experts Group (JPEG) Files: 

JPEG is a file type which stores images.  The images are made up of tiny pixels, and the better the pixels the better the resolution of the image. Each color has a hexadecimal value.

Memory sizes can differ to different applications, there can be functions that take up more space than usual.

Data Dictionary Compression:

If a text file uses 1,000,000 characters and there are words that repeat themselves, using a Data Dictionary  will decrease the file size. The words which are common are replaced with numbers.

Lossy and Lossless File Compression:

Lossless File Compression, all the data bits from the original file are reconstructed when the file is again uncompressed. This is particularly important for files where loss of any data would be disastrous – for example, a spread sheet file.

Lossy File Compression is very different to lossless file compression. With this technique, the file compression algorithm eliminates unnecessary bits of data as seen in MP3 and JPEG formats.

ASCII:

We use ASCII in our daily lives since binary is nearly impossible to read. The ASCII table is easy to understand and saves a lot of time.

Memory and Storage

Memory and storage devices can be split up into 3 distinct groups:

  • primary memory
  • secondary memory
  • offline storage

memory and storage

Primary Storage:

Random Access Memory (RAM) 

Features:

  • temporary memory (the contents of the memory are lost when the power to the RAM is turned off)
  • it is used to store: data, files, or parts of the operating system that is currently in use
  • it can be written to or read from and the contents of the memory can be changed

The larger the RAM size, the faster the device will run since it can handle the things at once. The RAM never runs out of memory, it just gets slower and slower. RAM is much faster to write to or read from than other types of memory, but its main drawback is its volatility.

There are currently 2 types of RAM technology:

  • Dynamic RAM (DRAM)
  • Static RAM (SRAM)

Dynamic RAM (DRAM) 

Each Dynamic RAM chip consists of a number if transistors and capacitors. Each of these parts is tiny since a single RAM can contain millions of these chips. The functions are:

  • capacitor – this holds the bits of information (0 or 1)
  • transistor – this acts like a switch; it allows the chip control circuitry to read the capacitor or change the capacitors value

This type of RAM has to be constantly refreshed, about every 15 microseconds otherwise it will lose its value, the capacitors charge would leak away leaving every capacitor with the value of 0.

However:

  • they are way more cheaper than SRAM
  • they consume less power than DRAM
  • they have a higher storage capacity over SRAM

Static RAM (SRAM) 

SRAMs don’t need to be constantly, as it is much faster than the DRAM when it comes to data access. Even though DRAM is the most common use of memory storage, SRAM is usually chosen over because of its speed.

Read Only Memory (ROM) 

Features:

  • They are permanent memories which means that when power is switched off the data is stored
  • Data/contents of the ROM can only be read, not changed
  • Often used to store instruction when the computer is first switched on

 

dram

DRAM

sram

SRAM

Secondary Storage:

Hard Disk Drives (HDD):

HDD is the most common method of storing data on a device.  Data is stored in a digital format on the magnetic surfaces of the disks (or platters).  The HDD has has a number of platters which can spin at about 7000 times a second. Several read-write heads are used  so that all the surfaces can be accessed; data is stored in sectors and tracks in blocks. Access to this data is lower than the RAM. Many applications require the read-write heads to move in and move out several times to get to the right data blocks. This is called latency – the time taken for a specific block of data on a track to rotate around to the read-write head.

The common speed for HDD is 5400 RPM

60 Nanoseconds

Solid State Drives (SSD):

SSD’s have no moving parts, therefore all the data is retrieved at the same rate and there is no use of latency.  Most SSD’s use NAND chips to control the movement of data.

SSD’s also  use EEPROM technology (Electronically Erasable Programmable Read Only Memory). This mainly uses NOR chips rather than NAND.

SSD’s are beneficial since:

  • more reliable and robust (no moving parts)
  • Much lighter in weight and are thinner
  • Consume less power and usually dont get hot
  • No need to wait for SSD to ‘get up speed’ and also have a faster data access rate

25 nanoseconds

Offline Storage:

CD/DVD:

CDs and DVDs use a red laser light to write and read the data. Each disk has a single spiral track that runs from the center to the outer edge. They can either be written once then read only once or can be written to and read several times. DVDS can hold more data than CDs due to dual layering technology (the disks have 2 individual recording layers.

Optical Storage

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.

Optical Storage

Blu-ray Disks

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.

Optical Storage

 

Data:

data

 

 

Colors are either represented by RGB (Red, Green and Blue) or by CMYK (Cyan, Magenta, Yellow and Black)

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