4.2: hardware Flashcards
processor
- part of the computer that processes data by executing programs
- manages the rest of the hardware
main memory
- memory that can be accessed directly by the processor.
- The main memory consists of memory locations that store instructions or data.
- 2 types of main memory: volatile memory and non-volatile memory
volatile memory
loses its contents when the power is removed
non-volatile memory
keeps its contents even without power
RAM
- volatile temporary memory that has adressible locations
- Each location can be accessed randomly, so any instruction or data can be placed in any location
ROM
- non-volatile (permanent memory)
- different from secondary memory
motherboard
- main printed circuit board (PCB) inside a computer
- connects all the components of the computer together.
- Similar to a human nervous system, a motherboard transmits signals between a computer’s components.
what does GPU stand for
graphics processing unit
graphics processing unit (GPU)
- processor designed specifically to render graphics.
- In the early days of computers, the CPU was responsible for this job. Now that graphics have become more advanced and require more computation, specialist processors have been designed to process graphics more efficiently and to take the burden off the CPU
Rendering
the process of converting image data into the graphics that you see on the screen
sound card
- component needed to output audio signals to devices such as headphones or speakers and to receive an audio input from devices such as microphones
characteristics of RAM
- It is volatile
- You can read and write to it
- It is quicker to access than secondary storage
- It has the largest capacity of all main memory
characteristics of ROM
- It is non-volatile
- It is written by the computer manufacturer
- Usually stores the BIOS
- Smaller capacity than RAM
purpose of RAM
Stores data and
instructions
during processing
purpose of ROM
Stores boot-up
instructions set by
the manufacturer
volatility of RAM
Volatile, data lost
without power
volatility of ROM
Non-volatile, data
remains after
power switched off
read/write of RAM
read and write
read/write of ROM
read only
capacity of RAM
usually several gigabytes
capacity of ROM
a few megabytes in size
Cache memory
- Designed to make access to frequently used data much faster
- There are three levels of cache used by the processor, each level has a different capacity and access speed. The closer the cache is to the CPU, the faster it can read and write data, but the less it can store
level 1 cache
usually a part of the processor itself. This cache has the lowest capacity, but the quickest access speed
level 2 cache
In some processors, the level two cache might be built into the processor along with level one.
Level two is slightly slower to read but has a higher capacity than level one
level 3 cache
the slowest at reading and writing, but it is still roughly twice as fast as RAM.
Registers
- small memory devices
- provide faster access than both the RAM and cache but are only able to hold a few bytes at most.
- split into two categories: general purpose and dedicated
general purpose registers
used to temporarily store values generated by instructions if they need to be used again in the next instruction
dedicated registers
serve a specific purpose in the Fetch-decode-execute cycle
virtual memory
a way a computer system can compensate for a shortage of RAM
why virtual memory is used
To reduce the likelihood of lags, freezing or crashing, computer systems allocate a portion of secondary storage as virtual memory
flash memory
- Flash memory is non-volatile and can be both written to and read from
- flash memory is used as both storage and main memory
system architecture
the structure of the internal components of a computer system
Neumann architecture
- occurss in modern computers
- involves: a processor; a memory unit, which stores both instructions and data; connections for input and output devices; and secondary storage for data
fetch-decode-execute cycle
describes how instructions are retrieved and processed in order to run a program
what factors affect processor performance
number of cores and the size of the cache
computer architecture
the structure and organisation of a computer system. It specifies the components that make up a computer system and describes how these
are interconnected
what von neumann architecture consists of
- a Processor
- a Memory unit that can communicate directly with the processor
- connections for input and output devices
- Secondary storage for saving/backing up data
adress bus
used to identify the adressed location
data bus
used to transfer the contents to/from that location
control bus
used to synchronise and control operations
arithmetic calculations
addition, subtraction, division, and multiplication
logical operations
AND, OR, NOT
control unit
organises the execution of instructions, including managing the other components in the processor
what is control unit responsible for
- Ensures the execution of instructions in the correct sequence
- Decodes every instruction that the processor will execute
- Sends and receives control signals to and from other components
- Checks that signals have been delivered successfully
- Makes sure that data goes to the correct place at the correct time
Clock
- used to synchronise the operations of the processor components
- generates regular clock pulses by emitting a signal
Current instruction
registers (CIR) purpose
Holds the current instruction that the
processor is executing
Memory address
register (MAR) purpose
Temporarily stores the memory addresses
used when searching for data in RAM
Memory data
register (MDR) purpose
Temporarily holds the data that are read from or written to the main memory
Program counter
(PC) purpose
Holds the address of the next instruction to be executed by the processor
Accumulator purpose
Stores the result of any calculation
Fetch, decode and execute cycle
describes the basic operation of modern computers
fetch
Each instruction is fetched from memory (in order) and put into the appropriate registers. The
control unit can then access the instruction for the next stages
decode
- The instructions (which are received in binary) need to be decoded before they can be run. This is the process the control unit uses to work out what the other components need to do.
- Each processor will have slightly different encodings for instructions
execute
The control unit will tell the other components what they need to do in order for the instruction to work
purpose of adress bus
Carries address locations of stored data from the processor to memory and input/output devices
purpose of data bus
Sends the data to and from the processor, memory, and input and output devices
purpose of control bus
Carries signals that coordinate the operation of the components
system bus
adress, data and control bus together
facts about buses
- Each bus consists of a set of parallel — not single — lines
- Each connection of a component to a bus is made up of parallel lines
- Input, output, and storage devices communicate with the other components via I/O
controllers - The connection is only one-way from the I/O controller of the input device towards
the data bus - There is a one-way connection from the data bus towards the I/O controller of
the output device - There is a one-way connection from the processor towards the address bus
- There is a one-way connection from the address bus towards all the other components,
i.e., the main memory and the I/O controllers
cache
a high-speed memory that sits close to or can be directly on the processor; it is used
to store the instructions and data most frequently used
number of cores
Computers with more than one processing unit (core) are called ‘multicore processors’. For
example:
* Dual-core = two processing units
* Quad-core = four processing units
* Hexa-core = six processing units
* Octo-core = eight processing units
requiremets of secondary strogage
high capacity
low cost
fast enough for loading and saving files
reliable permanent storage
3 types of secondary storage
- Magnetic (hard) disk
- Solid-state disk
- Optical disc
magnetic storage
referred to as hard drives
oldest form of didgital storage
characteristics of magnetic storage
- mechanical devices with many moving parts
- means that it is more likely to fail
- works like a cd reader
advantages of magnetic storage
- large capacity
- lower cost than SSDs
- reliable
- do not degrade over time
disadvantages of magnetic storage
- not portable
- they are built to live insde a computer
- can be fragile
reading data from magnetic storage
To read the data, the head sweeps across the tracks on the spinning platters. A small magnetometer (a sensor that reads magnetic forces) reads the states of the magnetised dots
underneath the read-write head. The magnetised states of the dots on the platters are then
translated to 1s and 0s
writing data to magnetic storage
In order to write data onto the platters, the magnet on the end of the read-write head is used to generate a small magnetic field. The field causes the dots to switch state, becoming either
magnetised or not magnetised. When the magnetic field is taken away the dots keep their new state, allowing data to be stored until another magnetic field is applied
optical storage
Optical discs are a large family of different disc types such as CD, DVD and Blu-ray disc.
what does CD stand for
compact disc
what does DVD stand for
digital versatile disc
characteristics of optical storage
- made up of a set of layers. The base is usually polycarbonate, and provides the main structure of the disc. There is always a thin aluminium reflective layer on the disc’s surface.
- Each disc has a continuous track of data arranged in a spiral
advantages of optical storage
- light and portable
- relatively cheap
- reliable
disadvantages of optical storage
- lower capacity than hard drives
- slow seek time
- not rewritable
reading data from optical storage
laser is shone onto the surface of the disc. The pits and lands reflect different amounts of light. The electronics in the optical drive (installed in your computer) can interpret the changes in reflected light as 1s and 0s
writing data
- To write to R or RW discs, the laser burns new troughs into the reflective surface of the disc.
- RW discs use a chemical dye that allows the burning process to be reversed, allowing you to rewrite the data on a disc
R discs
- recordable
- can be written to once
- used to archive data
RW discs
- rewritable
- can be written and read many times
- used to back up files
solid-state storage
- caled SSD
- form of Flash memory used for the medium to long term storage of data
- has no moving parts
- usb stick is an SSD
advantages of SSD
- portable
- no moving parts so mechnical failure is less likely
- less heat generated
disadvantages of SSD
- number of times that a solid-state device can be written to is limited
- not suitable for long term archiving of data
cloud storage
- way to store and access files through the internet
- data is stored on servers with secondary storage decvices
advantages of cloud storage
- expandable
- files can be accessed from anywhere in the world
- backs up your files and provider takes responsability for your data
disadvantages of cloud storage
- requires and internet connection
- slower than other methods
- malcious individuals may gain access to your data
- data cna be lost
embedded systems
- a system designed to do a specific job
- cheap, low-power devices using simple technology and limited memory
examples of embedded systems
traffic lights
toaster
toy
