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Topic 4 - Computer Systems (Memory and storage - Magnetic (They have a…
Topic 4 - Computer Systems
Software Classification
Two types of software
System software - windows 10, IOS
Software that controls/manages the operation of a computer system. Deals with the running of the computer system. System software is designed to support the running of the application software. These are programs that are needed in order for the computer to function.
System software is split into two sections: Operating system and Utility programs.
Operating systems - windows 10, IOS, Mac OS
Utility programs - Anti-virus software, disk utility.
Application software - web browser, word processor.
Any program that the user uses to complete a particular task.
Memory and Storage - HDD
RAM (Random Access Memory) - A type of memory that can be randomly accessed at any time.
ROM (Read Only Memory) - A type of memory that can not be changed.
Hard Disk Drive - Used to store large amount of data, slower and less efficient use of power compared to the SSD.
Hard Disk Drive -
Advantages
Cheap, vast storage capability, fast write speed.
Disadvantages
Lots of mechanical parts, durability an issue, sealed unit due to disk head and platter precision and not very portable.
Faster than an optical drive
Slower then an SSD.
Capacity is in Terabytes.
System Architecture
ALU (Arithmetic Logic Unit)
Major components of the CPU. The ALU is responsible for the following:
Logical operations (AND,OR,NOT,...)
Logical comparisons
Arithmetic operations (addition and subtraction)
Bit - shifting operations (left and right)
Control Unit
The control unit is inside the CPU and is used to control the flow of data within the system.
Controls sequential instruction execution.
Interprets instructions.
Sends and receives signals from other computer devices.
Handles tasks, such as fetching, decoding, execution handling and storing results.
Clock
The clock is used to synchronise components in the computer system. A clock signal goes from '0' to '1'.
Sends a continuous series of electronic pulses.
The number of clock cycles is measured in Hertz (Hz).
A clock of 100 Mhz means that in one second there are 100 million clock cycles.
Clock speed
Three factors that affect the CPU performance
Clock speed - Cycles per second measured in Hertz.
Number of cores - The number of duplicate processors linked together on a single chip.
Cache sizes / types - Super fast working memory.
Cores
A dual-core processor has two processors in the same integrated circuit, linked together.
Multi-core processor
A dual-core processor has twice the power but does not always perform twice as fast, because the software may not be able to take full advantage of both processors.
Cache
Cache Memory
Expensive and very fast memory.
On the CPU chip.
Accessed faster than main memory.
Cache Memory in action
Then will look in RAM if the data was not in cache.
Copies from RAM to cache.
Processor will look for data in the cache memory first.
When spaces is running low, older content will be replaced by recent data.
Bus
A bus is used to connect one or more components of the computer system.
A bus use a collection of parallel wires to transfer signals from the components.
The system bus contacts the components together. There are three types of buses within the system bus.
Data - Responsible for transporting the actual physical data, the bits and bytes of information between memory and the CPU.
Address - Used for communicating the physical addresses of the computers memory elements / locations that the CPU wants to access.
Control - Carries command and control signals to and from very single connected device.
Fetch-Execute Cycle.
Fetch - Causes the next instruction and
any data involved to be fetched from main memory.
The CPU operates by repeating three operations:
There are 3 parts to it: Fetch, Decode and Execute
Decode - Decodes the instruction.
Execute - Carries out the instruction.
Decode
The control unit decodes the instruction.
It determines how many operands are needed and the steps that need to be taken to execute the instruction.
Execute
Depending on what the instruction is, this could involve fetching data from memory and loading or adding it into a register, or jumping to another instruction in the program.
After this stage, the cycle returns to the beginning and starts again
The instruction is executed.
Role of an Operating System
An OS is software that is a collection / suite of programs that then interface's between the user and the computer. The OS is designed to control the operations of the computer.
The OS hides the complexity of the computer from the user and other software. Linking the hardware, software and user.
Common tasks that the OS performs include: manage any input/ output devices / files / memory.
To provide a software platform on which other programs can run or to run application software.
To hide the complexity of the hardware from the user.
Purpose of an OS
An OS is needed to provide an interface between appliance software and the hardware.
The OS is responsible for managing:
Processor access, Memory management, Input / Output devices, Applications, File management, security.
In short... An OS is responsible for managing the resources of a computer system.
Secondary storage - Optical Disks
There are a number of different formats that can be used for optical disks, but they all use lasers.
Each of the above technologies are slightly different but use a similar idea of reflecting a laser from the surface.
When writing data to a disc a high powered laser will "burn" the disk which will create a pit. When reading data a lower powered laser is used with a light sensor. The edge / start / end of a pit will deflect not reflect the laser onto the sensor.
This could be used to represented a 1 and 0.
Advantages and Disadvantages of Optical
Advantages - Cheap, very easily portable, takes up little space physically.
Disadvantages - Less capacity compared to other types, easily damaged/ scratched, requires a CD reader, slow write speed. Faster than nothing, slower than everything (HDD's and SDD's). Capacity - Blu ray (50GB), DVDS (4.7GB), CDS (700 MB).
Memory and storage - Magnetic
They have a magnetic material on the surface.
Change in magnetism represents binary code.
A number of disks are arranged in a stack.
Magnetic - Hard Disk Drive - A secondary storage device made up of metallic disks that stores data magnetically.
The collection of disks spin.
Each disks will have a head that will read or write data.
The heads are moved by an actuator arm across the surface of the disk - they do not come into contact!
Surface of the disks are arranged into tracks
Each track has a number of sectors which can by individual addressed by the OS.
