This is a detailed and organised 60+ paged notes (handwritten), with diagrams, examples, and slide screenshots. It was written/summarised from the PG Online resource, and covers the whole IGCSE Cambridge Computer Science 0478 syllabus. It helped me and a few other students score an A* in the May-J...
Scale sense
no ef possible
30 KiB
=
1 page of text combinations
3 MiB =
small digital coloured photo
650 MiB = music CD capacity
4 5 GiB
. = DVD capacity
Most & least significant bit
1 TiB =
Hard disk capacity O 110 118 &
most
& &
significant
last
sig.
double (largest (smallest
Binary base I
&
F
128643216 842 I Calculate value that
largest
eg .
8 I J & I 08 I can be represented :
value 64 16 8 1
denary
+
in +
(no 2) bits)
= +
.
base 18
89 2 1
-
I
↓ from O-result
range
Sbits , 0-255
eg
.
,Binary data in
computer
A central
processing unit (CPU) is made from logic gates which process
many ,
data Each
(PU has
.
a number of registers which each store binary data
,
.
the result
When a
calculation/processing occurs , is also stared in a .
register
Hexadecimal AKA . nex
* Uses base 16 (0-15 only
denary & 123456789101112131415
nex 0 123456789ABCDEF
Hex to
denary Denary to nex
Hex 2A 18
:
Denary :
&
= (2x16) +
18 18 + 16 = I remainder 2
More than 2 digits :
=
42 is denary =
12 in nex
2A5
-d Y
Binary hex
to (2x134+ (8 16) + 5
+ =
667
Idenary
1110 14 Einhex
E
= =
* need &
1110 8101
· 181 = 5 in hex
=
E5 Probably won't
Hex to
binary
/3 00 ,
=
=
8811 8181
10
Advantages of nex
1 . Easier for humans to understand (shorter representation of binary
.
2 Easier to remember and enter
. Less
3
likely to make error (fewer digits)
& the more
frequently we sample sound (Increase sampling rate)
& the more accurately we record the wave height (Increase resolution
* Both will increase file size (bit
depth
2
Hearing range
Lossy compression MP3 & AA 20 -
20 , 000 Hz
Removes sound can't hear .
-
we
easily younger people
R useful for hear
higher
downloading/streaming
Image resolution
Number of pixels in the image
HD
/high definition) TV ->
> 1920 x 1080 pixels
-
lot iPhone >
- 320 x 480
pixels
-
Colour depth/bit depth
of bits
per pixel
Number
knumber of color combinations. /available colours
greater range of
better
*
higher color depth >
- colors , .
quality
. 8-bits per pixel
eg 28 256 colors = =
Imagesize Resolution x color depth bit pattern
~
PBM monochrome
images
Stores :
* dimensions
Image
* Black white with
or 1 or O
,Colour values
[
Expressed hexadecimal read
,
as
denary RBG values in easier to
& Range =
0-225 (8-bits per color) & write ,
remember ,
Compression to reduce file size (sound image , ,
video
* opposite to decompression (for lossless only)
Lossy compression /JPG GIF. , MP3)
Permanently loses some data
& Cause small mistakes or
digital artefacts
,
Lossless Compression (PNG TIFF)
doe
,
Doesn't lose any original data
> Finds
repeating data
-
Run Length Encoding (RLE) RLE 5130
↑
=
* Algorithm to compress data/reduce data stored
* uses frequency/data pairs
&
1 white 8 black
eg .
: =
,
Loss of data Bandwidth
Possible to reduce : Maximum volume of
All loses data data transmitted over
S
-
resolution
-
color depth (permanently) internet connection
rate
sample but reduce in
given amount
-
a
-
bit rate file size of time
.
Using compression -
often for files & data sent via internet
*Transmission time reduced >
-
download faster
* Data allrance go further
* Less bandwidth required
* Less files
storage space to save
,Benefits of compression
* smaller files fewer packets faster
=
=
transmission time
>
-
quicker to complete transmission
>
- reduce traffic over the internet
* Reduce danbad time
>
-
streaming is possible
#Images in web pages appear faster
* Reduce disk/servers
space on
Buffering Happens if dennload speed is slower than
playback speed
.
Files for videos and streaming are
compressed
*TV computer decompress data video
or as it
plays
* Buffer sufficient amount in case network occasionally
Slow
k If web/server detect slow connection it sends alternative
,
lower quality file
.
, Unit 2 -
Data transmission and
encryption
Revision Notes
Data packets
To send large amounts of data through networks,
data is needed to be broken down into smaller packets .
apacketmuudes
:
Destination address
Header
E Originating
Packet number
address
(to restore order
Payload -
The content
Data that indicates
Trailer
S end of
Checksum
packet
(to check for errors)
Packet switching
The
process of sending data through a network :
1 . Data break into smaller packets
.
2 send packets through network
.
3 Routers contro route taken
may arrive cut
of
4
correct order
. ~ order
. Reorder packets into
Network components
Routers manage the
rentes so there is less
traffic
Carrive faster)
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