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Computer Science Paper 1 (Computer Systems and Hardware) (Von Neumann…
Computer Science Paper 1 (Computer Systems and Hardware)
Von Neumann Architecture
"Architecture" Means the components inside a computer system and how they are interconnected
Many different architectures each with different arrangements of components
The most well known being the von neumann Model
The VNA involves a Control Unit (CU), Arithmetic Logic Unit (ALU), Memory Unit (MU)
The Control Unit and The ALU are both Sub components of the CPU
The CPU is connected to the memory by Bus
Other buses are used to connect Inputs, Outputs and Secondary storage devices (Not part of VMA)
Control Unit
The control unit coordinates the activity of the other components, Program instructions may require data to be input, output or stored.
Interprets instructions
Manages the computer's response
ALU
Performs arithmetic (+ - * /)
Performs Logic Operations (AND OR NOT)
Performs comparisons (< = >)
By combining these operations in different ways, computers can perform a limitless number of tasks
Registers
Small but very high speed storage area
Inside the processor
The Control Unit, The ALU and Registers are what make up the CPU
All three of these collective purpose is to execute instructions performed upon data
Memory
Memory is divided into many uniquely identifiable locations
Each of these locations can be separately addressed by the Control Unit
For example: Location 1 could have the command "ADD" stored and Location 2 could have "10" and Location 3 Could have "7" So the control unit would write the Location 4 "17"
A piece of data or an instruction moves along a bus
Fetch Execute Cycle
An instruction is read from memory into the processor
The control unit decodes the instruction to determine how to execute it
The control unit may call upon the ALU, Memory, Secondary storage Or even input and output devices to perform the task
Within the processor various Registers will store the current instructions, Memory location of the next instruction and Other pieces of relevant data
The Fetch execute cycle can occur billions of times per second
Data moves between the memory and the processor at the speed of light
Memory is both Finite and Volatile
Memory is Finite because it there is a limited amount of Memory Available
It is also volatile because the contents are wiped when the computer is turned off
For data to be stored long term, Secondary Storage is needed.
Secondary Storage devices
Solid State
USB flash drives
Hard Disk Drives
DVD drives
Secondary Storage devices allow programs and data to be stored even when the computer is turned off. Without secondary storage you would never be able to store you work and return to it
Embedded Systems
What makes an object a "Computer"
Accept data from an input device
Store data
Combined of Hardware & software
Process data
An embedded device is a device which forms part of a larger device
These bigger devices can be Mechanical or Electrical
Many different things can be an Embedded system
An oven is an Electrical device with inputs (Changing the temperature of the oven with a bottom AND Setting a timer on the over and also a Sensor for the temperature ) and the output is the Heating element of the over. So you press the button to increase the temperature and the temperature increases.
A Petrel pump is a Mechanical device with inputs (Squeezing the lever to release petrel from the pump) The outputs are the signal to the pump to actually release the fuel and a signal to the digital display to update the amount of petrel used and how much it costs
Embedded devices constantly moniter the input devices, Adjusting the output to match the data given
Every embedded device includes a processor. These processor are usually much less powerful than one found your average desktop PC
All these Input devices, Individual buttons, Sensors and connections all send signals to the processor.
Output devices are also connected to the processor to be able to receive signals from the processor (For example, Display screen, LEDs Speakers Motors)
The processor loops through its instructions many times per seconds
The processor decides depending on its code. How to appropriately respond (And then output signals are generated accordingly)
Embedded devices are literally everywhere. There are many different ones in cars for example. Cruise Control is a process run by an embedded system and so are Climate control and even things like SAT NAVS
RAM & ROM
Computers need to store data. Without this computers wouldnt have the ability to remember instruction number one or a piece of data as soon as instruction number 2 starts
Things need to be stored during a programs execution
Different types of data require different types of storage
The main types of Memory are: RAM, ROM, Virtual Memory, Cache Memory and Flash Memory
RAM
Random Access Memory
Main Memory
Stores programs that are currently running
Stores data that is currently in use
These programs and data are loaded from the secondary storage
RAM has a very high speed (Especially compared to secondary storage)
Once programs and data are no longer need they can be overwritten
It's capacity is quite small, compared to secondary storage
RAM is Volatile (Contents are lost when the computer is shut down
ROM
Read Only Memory
Contents can be read but not changed or deleted
ROM Contains data that is never expected to be changed
It is permanent memory
Hold firmware that boots up the computer
Contains a pointer to the memory location where the operating system is stored
When the computer is turned on, ROM is accessed and the pointer shows the computer where to look.
As the Operating system is not likely to be moved, It is Appropriate to store this pointer in ROM
Virtual Memory
Used when a computer requires more RAM that it possess
If a 6 Gigabyte program was being used and only 4 Gigabytes where available then the two would be stored on a reserved section of backing storage
Behaves like an extension of RAM (Only be used when necessary as it is quite slow)
Cache Memory
Type of ram that can be accessed more quickly than the rest of RAM
Directly connect to the CPU
Much smaller capacity than the rest of RAM
Typically not enough space for an entire program
Used for either data or instructions that will be accessed repeatedly
Cache data is volatile
Flash memory
Most common are in the form of SSD's and things like Flash Drives
Each bit of data is stored in flash memory using a pair of microscopic transistors
1st transistor either holds a charge or does not hold a charge to represent a 1 or 0
2nd transistor can read the state of the first transistor
Transistors can be made increasingly smaller
Can contains many billions Transistors
Storage capacity is increasing over time
Use of secondary storage
Any device that is use to store data is known as a storage device
RAW data enter a computer system by an input device
Input goes to the CPU and then the CPU Processes it and send it to an output device
These inputs can also be stored for later use as a named file
Factors to decide what storage device come down to: Capacity, Speed, Portability, Durability And Reliability
Storage devices can be Internal (Inside the computers case) and External (Outside the computers case connected by using USB)
Hard Drives are the most common storage devices
Internal storage is need to hold the operating system
It could also be used to store the actually applications that you use (Word or Discord for example)
Internal allows data to be loaded rapidly
Internal devices are connected directly to the Motherboard
External Devices are connected through a Hardware Interface
External are considerably slower to access
When a Internal storage disk fails. ALL the data and applications may be lost. (This can be avoided by using more than one harddisk)
an alternative is to use external drives as back ups
External are connected mainly by USB
With a External the user can still, Open, Edit and Transfer files in the usual way
external are good because they are portable
External are good to bakc up files, transfer files ETC
files transfer speeds are slow, take up space, and are vulnerable to theft
Types of Secondary storage
Secondary storage is used to store large amounts of date
Secondary storage is Non-Volatile
Contents can be safely stored even if the power supply is cut
Usually many times the size of RAM
Internal Hard drive, Flash Drive, Disk Drive are the most common types of secondary storage
Computers are digital devices meaning they store and Process binary data
Secondary storage devices are designed to store 0 & 1 in different ways
The three main Classifications of Secondary storage are: Magnetic, Optical and Solid State
Magnetic
Round disc and a read and write head
Billions of microscopic metal fragments
Either Magnetized or not magnetized to represent 1 or 0
The read and write head can determine the state of any individual fragment and change each fragment from one state to the other
DIsk spins so the correct sector is facing the read/write head
Then moves to the right trict on the disc to access the desired fragment
If a device is magnetic, the word Disk will always be spelt with a K
Very cheap
optical storage devices
Use lasers to read and write data
CD Drives, DVD/Blueray Drives
Each disk contains billions of pre-determined locations
each locations might have a mircroscropic hole to represent a 1 or an 0
It measures the distance it travels before it hits something
If a Device is optical, the word Disc will always be spelt with a C
Less cheap than Magnetic
Solid State Devices
No moving parts
much faster than either magnetic or optical devices
Each individual bit is stored using a pair of transistors
1 transistor either contains or charge or does not, representing either a 1 or a 0
The other transistor is capable or reading the state of the first transistor
Charge arrives VIA electronic circuitry and is read in the same way
Because there is no spining disk or read and write head saving or loading data takes place much more quickly
(Not as quick as ram)
Non-Volatile
Typically the most expensive
Data Capacity Requirements
Mid-90s Computers on adverage had 250 MB of storage (Storing about 2 billion bits magnetically)
by 2015 most Computers on average have 2 TB of storage (Storing around 16 Trillion bits)
To put this in to prespective. A desktop computer from 2015 could store the same amount as 8000 computers would in the mid 90s
As data capacity's have risen, so has the size of the files that need to be stored
A Bit is the smallest unit of data and can only be a single 1 or a single 0
a Nibble (/Nybble) is made up of 4 bits
a Byte is a series of 8 Bits (This is enough to store a single character for example "A""a""6"";""_")
Patters of bits are used by computers to represent everything including Numbers, Characters, Symbols, Images, Sound, Video, Instructions
1024 Byte's = 1 Kilobyte
1024 Kilobyte's = 1 Megabyte
1024 Megabytes's = 1 Gigabyte
1024 Gigabyte's = 1 Terabyte
1024 Terabyte = 1 Petabyte
1024 Petabyte's = 1 Exobyte
1024 Exobyte's = 1 Zettabyte
1024 Zettabyte's = 1 Yottabyte
Example Question: How many bits are needed for a 7KB file? 7 x 1024 = 7378 Bytes, 7378 x 8 = 59024 Bits
Purpose Of The CPU
Central Processing Unit
Process Data
It can Search, Sort, Calculate, Do decision making tasks
Feetching
Decoding
Executing
Main Parts: Control Unit (CU), Immediate Access Store(IAS), Arithmetic Logic Unit(ALU)
Control Unit Deals with hardware and fetches instructions
Immediate Access Store Holds data and the program needed
Arithmetic Logic Unit Processes data
All computers contain atleast one CPU
CPU deals with all data and processing no matter what you are doing on your computer, From homework, to listening to music, to playing games, to talking with your friends
Modern CPU's have multiple cores, this is the number of processors in the CPU
A multi core cpu allows many simultaneous tasks to go on at once
Dual Core means 2 processors
Quad core means 4 processors
CPU's are so fat you may think that it is processing all of these things at once but its doing them one by one its just so hard to see as it is so quick
Clock Speed (hz) is how many tasks a processor can do per second
Modern computers clock speed are measured in GigaHertz means the processor can process several thousand million tasks per second
Fetch, Decode & Execute
When a program runs on a computer the data it is using and program itself is loaded into the RAM by the OS
fetch
Retrieving an instruction from a memory address
the cpu sends the address of the instruction it wants VIA a hardware path called the Address Bus
The RAM finds the instruction with the correct address and sends it back to the CPU VIA the Data bus
The data is stored in the register
Decode
CPU breaks down instructions into some