Memory & Data Storage Flashcards
MIDI
Musical Instrument Digital Interface
Standard adopted by the music industry for controlling devices such as synthesizers and sound cards and electronic instruments.
Stores commands on how to play sounds – NOT SOUNDS
Mp3
File compression system for music which does not noticeably affect the quality of the sound
Removes sound humans can’t hear well
If two sounds playing at the same time the softer sound is removed
Uses perceptual music shaping
Differences between MP3 and MIDI
MP3 a digital recording of sound Mp3 produced by recording software Mp3 a compressed file format MIDI Instructions of how to make sound MIDI Non-audio recording MIDI File created using digital musical instruments MIDI Produced by synthesizer
Image Capture
Image converted from analogue to digital (ADC) Image turned into pixels Each pixel given binary value Each pixel given a colour Pixels form a grid Pixels stored in sequence
File Compression
Can be lossless or lossy
Uses a compression algorithm
Advantages of Compression
Smaller file to transmit
File transmitted quicker
Uses less bandwidth
Lossless
Code must be exactly the same as the original
If not the same as original file will not work
A (compression) algorithm is used
No data is removed in the process
Used for Programs & Text Files
Repeated words (are identified) and are replaced by an index
The number of times the word appears is stored
Lossy
E.g. Video file (Mpeg)
Makes the file smaller than lossless
Quality can be reduced but the file will still run
Redundant data can be removed
Used when no requirement for file to be exactly same as original
Text File Compression
Use lossless
Repeated words can be indexed
Repeated words sections e.g. ‘ou’ can be replaced with numerical value
Can be saved a s a zip file
Primary
RAM (Random Access Memory)
ROM (BIOS)
DRAM
- Tiny capacitors that leak electricity
- Requires a recharge every few milliseconds
- Inexpensive
- Slower than SRAM
- Can store many bits per chip
- Uses less power
- Generates less heat
- Used for main memory
SRAM
- Circuits similar to D flip flops
- Holds content as long as power is available
- Expensive
- Faster than DRAM
- Cannot store many bits per chip
- Uses more power
- Generates more heat
- Used for cache
ROM (BIOS)
Non-volatile memory chip
Primary memory
In a microprocessor holds the BIOS
Can’t be written to
PROM (Programmable read-only memory)
It can be programmed by user. Once programmed, the data and instructions in it cannot be changed.
PROM (Erasable Programmable read only memory)
It can be reprogrammed. To erase data from it, expose it to ultra violet light. To reprogram it, erase all the previous data.
EEPROM (Electrically erasable programmable read only memory)
The data can be erased by applying an electric field, with no need for ultraviolet light. Erase only portions of the chip.
NAND chips
More expensive
Faster read
Erase byte
CACHE
Cache holds the information from the RAM that is most actively used, and accessed most frequently.
The computer system will run faster as the slower main memory will need to be accessed less frequently.
When the processor needs to read from the main memory, it first checks if a copy of the data exists in the cache.
If the data to be read do not exist in the cache, the data are first copied to the cache and then used.
When the processor needs to write to the main memory it does so through cache memory.
HDD (hard disk drive)
Uses platters Platters divided into tracks Platter is spun Read write arm moves over platter Magnetic fields control magnetic dots of data Magnetic field determine binary value
SSD (solid-state drive)
Non-volatile memory
Uses NAND flash memory
Why SSD replacing HDD
No moving parts (more reliable in a portable device) Use less power Smaller (good for portable devices) Faster data access Run cooler Run quieter
Why HDD still used in web servers
Cheaper for large amounts of data
Greater longevity for read/write functions
Don’t need faster speed of SSD
Expensive to change technology
Off-Line Storage
Not directly accessed by CPU
Non volatile
Can easily be disconnected
DVD
Uses 1 spiral
Red laser used to read/write
Dual layer technology
DVD-RAM
Uses concentric tracks
Allows read/write operations at same time
DVD-R Vs DVDRAM
DVD-R one spiral track DVD-RAM several concentric tracks
DVD-RAM can be written to and read at same time; DVD only allows read
DVD-R only allows read; DVD-RAM allows read and write
DVD-RAM can have direct access because of concentric tracks
Blue-Ray
Uses blue laser
Uses single1.1mm polycarbonate disc
Tape v SSD in Server
Greater longevity – more read and writes Speed is sufficient Cheaper per unit of data – better value No portability requirement Trusted technology
How SSD works
Flash memory
Uses transistors
can be NAND/NOR tech
When stored in transistor data is converted from 1 to 0, 0 to 1
Controls the flow of electrons using transistors.
Stores data by flashing onto silicone chips
EEPROM tech
How USB works
EEPROM tech
Uses transistors
When data is stored on transistors data is converted from 1 to 0, 0 to 1
Transistors control the flow of electrons.
flashed onto silicon chips
read and write simulationously
TLS vs SSL
TLS makes use of session caching
TLS separates handshake and records
Possible to add new authentication methods
