Chapter 1: Data Representation
Formulas
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Hexa to Denary is. First write it like this e.g
16^2 x C + 16^1 x 8 + 16^0 x F
3072 + 128 + 15
=3215
Denary to Hexa is obtained by dividing the value by 16
2004 divided by 16
125 divided by 16 remainder 4 from last
7 divided by 16 remainder 13 from last
Remainder 7. Then write remainders bottom to top 7 D 4
Two’s complement is found by using this format
-128 64 32 16 8 4 2 1
RLE
Definitions
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Denary: “base 10 number”, regular numbers, 1s 10s 100s.
Binary: “base 2 number, values in 1/0, headings in 2^1 ect
Hexa: “base 16 number”, values in 0-9 and 10-15 are represented
by A-F, heading values in powers of 16
Mac Address: number used to identify device on network written
in 6 pairs of hexa digits e.g NN-NN-NN-DD-DD-DD, NN means
company code, DD means device code
IP Address: virtual location written in two forms IPv4 which is a 32
bit number written in denary or hexa (77.76.9e.01) or IPv6 which is
a 128 bit number written in 8 pairs of 4
(a8fb:7a88:fff0:3d21:2085:66fb:f0fa)
HTML: used to write web pages, is a markup language that can
also represent colours in Hexa form (#FF9966)
Shifting left/right: a operation used to move all the 1s in binary
Sound: sample rate (bits/sample) x sample res (sample/sec) x
time
Image size: Colour depth x resolution
Lossy compression: compression type that deletes data,
png/mp3/4
Lossless compression: compression technique that doesn't
delete data or any details
RLE: It’s a form of lossless compression that relies on repeating
values
Chapter 2: Data Transmission
Definitions
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Data Packets: Small chunks of data from a file that are used to improve delivery speed. Roughly 64 KiB big and the three parts
of a packet are the header, payload and trailer.
Header: Contains source and destination IP, packet sequence and number/size of packet.
Payload: Contains the 64 KiB of data.
Trailer: Contains method of packet identification and method of error checking.
Packet Switching: when a photo is broken in packets and sent each on a different route to improve speed
Types of data: Simplex (one direction), half duplex (both directions but not at same time) and duplex (both).
Methods of Transmission: serial ( one bit/sec slow but good for long range) and parallel (multiple bits/sec fast but only good
for short range).
USB: serial data transmitter that using common input/output ports
Parity checks: Method of verification using leftmost digit if it is 0 then the sum of the 1s is even if 0 then they should be odd if
not then corrupted.
Checksum: Verification method reliant on checksum being calculated by algorithm sent over and then compared after sending
Echo Check: Data is copied and sent over then returned and double checked to see for error then sent again (worst method).
Encryption: Data is altered so it can’t be read when a hacker intercepts it, you need both a public and private key to view the
files/messages
Chapter 3: Hardware
Definitions I
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System Clock: Helps synchronize PC, produces time signals on the control bus to stop computer from crashing.
RAM: holds all data and storage needed to be accessed by CPU.
CPU: Takes data and storage and puts them in temp RAM.
Temp RAM: key data for app that’s being run is stored here.
CIR (current instruction register): Stores current instruction that is being decoded and executed.
MAR (memory access register): Stores address of the memory location currently being read or written.
MDR (memory data register): Stores data which has been read/written from memory.
PC (program counter): stores addresses for the next instruction.
System bus: parallel transmission components that transfer data in a computer.
Address bus: carries addresses through computer in unidirectional format between CPU and memory. Wider bus = More memory.
Data bus: carries data in bi-directional format.
Fetch Decode Execute cycle: The CPU fetches data/instructions from memory, stores them in registers and then they are decoded and executed.
Cores: The amount of cores can improve performance as a single core has a ALU, control unit and registers.
Cache: cache is memory located inside the CPU itself, cache is small and only for significant files, it is faster than RAM.
Embedded System: a combination of hardware and software used for a specific function.
Micro Controller: has CPU, RAM, ROM and other peripherals on a singular chip.
Microprocessor: an integrated circuit with only CPU on it.
System on Chip: may contain microcontroller, CPU, memory, input/output ports and secondary storage.
Barcode Scanner: a barcode is made of black and white lines of varying thickness, Two long thin bars separate the left from the right numbers are
represented as a series of lines in patterns depending on if it is in the left or right.
Scanning Process: a red laser/LED reads the barcode, light reflects of the barcode to read patterns which are then converted to binary.
Chapter 3: Hardware
Definitions II
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QR code: a type of code that can hold more information.
Touch screens: the two methods of making touch screens are surface capacitive (4 corner sensors make electric field to detect finger) and Projective
capacitive ( transparent conductive layer makes x,y matrix when tapped electrostatic field is disturbed). Two major types of screens are IR (glass with
array) and resistive (electric layer is used by pressing really hard).
Actuator: A mechanical or electromechanical device controlled by a computer.
Memory: internal devices that are used to store data which computer can directly access.
Primary memory: It is directly accessed by CPU and is made up of RAM, ROM and cache.
Secondary storage: it isn't directly accessed by CPU it can be inside and outside the computer and is permanent.
RAM: when you run or execute a file the necessary files are moved to RAM temporarily.
ROM: ROM is permanent type of primary memory, it stores vital system files which can’t be altered.
DRAM: RAM variant that is constantly being refreshed
HDD: It stores data on magnetic disks that spin 700 times per second. Read write heads consist of electromagnets that read/write data. Data is stored
in sectors/tracks. They also come in portable variants.
SSD: SSD is quicker than HDD due to there being no moving parts, it is also faster and more efficient than HDD
they store data by controlling the movement of electrons with NAND/NOR chips
CD/DVD: laser is used to read/write data which is stored in a thin alloy inside pits and tracks on the spiral track
DVDs store more data as they are dual layered
Blu-Ray: they use faster tech like a blue laser and smaller pits. They are also encrypted and come in 27-40GB
depending on if they are dual layered or not.