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1.2 Memory and storage - Coggle Diagram
1.2 Memory and storage
1.2.3 Units of Storage
Bit (0/1)
Nibble (4 bits)
Byte(8 bits)
Kilobyte(1024 Bytes)
Megabyte (1024 Kilobytes)
Gigabyte(1024 Megabytes)
Terrabyte(1024 Gigabytes)
Petabyte(1024 Terabytes)
1.2.1 Memory
RAM
- Random Access Memory
CPU cannot access software or data unless it is in RAM.
Contents can be accessed at
any time, in any order
.
Measured in
gigabytes
(GB)
Volatile
Volatile
- loses contents when power is turmed off.
Non-volatile
- data stays when the power is off.
ROM
A microchip connected to the mother board.
Cannot be changed or overwritten.
Non-volatile
Commonly used to store
BIOS
.
Virtual memory(Main Memory)
If RAM is full, inactive data and instructions can be moved to virtual memory to free up space.
Stored on the computer's hard disk.
Much slower than RAM.
Can be accessed directly fromthe CPU
Volatile
Flash Memory
Non-Volatile
More expensive
(For the same ammount of storage)
Has a limit to how many tims it can be written/ changed.
1.2.2 Storage
Magnetic storage
Stores data in
domains
(tiny magnetic particles)
Examples:
Hard Disk and Magnetic Tape
Advantages:
-
Huge capacity
-
Long term
storage
-Cheapest/GB
Disadvantages:
-
Magnetic fields can erase data
-
Not portable
(Screwed into chassis)
-Slower than Flash
Optical Storage
CD's, DVD's and Blu-Ray
Laser beam burns tiny pits into the surface of the media.
Pit = 1
- Advantages:
-Media is very
portable
-
Low cost
for storing
small
amounts.
-
Immune to magnetic fields.
- Disadvantages:
-Not as robust as other options.
-Slow to write to this media.
-Sow to access data from.
-High cost for large data storage.
Solid State Storage
USB, SSD and SDHC.
Holds data using
electronic switches
.
Open Switch= 1
- Advantages:
-Very portable.
-
Robust.
No moving parts.
-
Fastest
data access.
- Disadvantages:
-
Expensive
(/GB) compared to magnetic storage.
-
Limited number of times can the data be changed/ written to - Reliability issue.
1.2.4 Data Storage
Images
Colour depth
To add colour to an image, more bits are required fot each pixel.
The
number of bits
determines the
range of colours.
This is known as
colour debth.
Metadata
Metadata tells the computer system the file type, resolution & colour depth.
Pixels and Resolution
Pixels
are the
building blocks
of images. Each pixel is stored as a set of binary digits (bits).
Resolution is the
number of pixels
there are in an image.
The
higher the resolution
, the
more pixels
there are in the image, the
more storage space is required
(larger file size), the
higher the picture quality
.
Sound
Sample Rate
-Speed-
How often/second you record the amplitude of a sound wave.
Bit Depth-
The amount of
detail
we're capturing each sample.
https://www.youtube.com/watch?v=Ed7AFAzB8PM
Bit Rate= Bit depth x Sample rate
Characters
Character Sets
Extended ASCII
Full 8 bits (no check digit)
256
possible characters
Most languages.
ASCII
8 bits, but leeftmost bit is a check digit.
127
possible characters.
Only English is represented.
Unicode
2 bytes
65,000+
possible characters
All world landuages.
Numbers
Binary
- Hexadecimal
(Base 16: 0, 1, 2, 3, 4, 5 , 6, 7, 8, 9, A, B, C, D, E, F)
-Write up in binary, then half it to 2 nibbles, then convert into hexadecimal.
Binary shift
to the left -> multiply by 2
to the right -> divide by 2
overflow error: if the shift (to either side) would result in a 1 being lost, this results in loss of accuracy.
1.2.5 Compression
Lossy Compression
some data is removed to reduce of data/file size.
Reducing colour depth-reduces the range of colours that the image contains
JPEG files tend to be smaller in size
MPEG file format compresses audio and video.
Lossless Compression
file size is reduced without loss of data, but it doesn't reduce it that much.
files that we do not want to lose data from:
-text files
-spreadsheets
-financial records
-emails
PDF allows lossless compression of text documents
GIF is a lossless image file format