4 Computer Systems Flashcards
What are Some types of hardware?
Input/Output devices
Secondary Storage
Primary Storage
Processors
What do input/output devices do?
I/O devices allow users to input data into the computer, or receive a data output from the computer. E.g. Keyboard Mouse Monitor Speakers
What is secondary storage?
Secondary storage is the memory in which the computer can store the data or instructions which are NOT currently in use.
Not all computer systems use secondary storage.
E.g.
Hard Disk Drive (HDD)
Solid State Drive (SSD)
Compact Disk (CD)
Flash (USB Drive)
What is Primary storage?
Primary storage is the memory in which the computer can store the data or instructions that are currently in use.
The two main types of primary storage are:
Random Access Memory (RAM)
Read-Only Memory (ROM)
What are processors?
A processor is a special component that processes data and instructions to control other components within the computer.
The two main types of processor are:
Central Processing Unit (CPU).
Graphics Processing Unit (GPU).
What are two types of computer systems?
General Purpose systems
Embedded systems
What are General Purpose systems?
General purpose systems are capable of performing many different tasks. E.g. PCs Macs Smartphones
What are embedded systems?
An embedded system is a computer system which is built into another device to support its operation. E.g. Washing machines Cameras Printers
What are transistors?
Transistors are electrical components made from semiconductor materials that can act as electrically-controlled switches.
Transistors can be used to temporarily store data, for example in some forms of primary storage (memory).
Why do we use binary form?
Underneath the surface, computers are electrical devices that process information by controlling the flow of electricity through billions of wires and transistors (electrical switches) inside the central processing unit and other components.
The presence of electricity represents a 1, and an absence of electricity represents a 0.
What are the transistors in the CPU used for?
Inside a Central Processing Unit (CPU), transistors are arranged into circuits to perform operations such as calculations when electricity is passed through them.
For example, transistors can be arranged to form an ‘adder’ circuit that can accept two binary numbers, and output the sum of their values.
Modern CPUs contain over 3 billion transistors, allowing them to perform billions of calculations per second.
What are logic gates?
Logic gates are when multiple transistors are are arranged together to form more complex switches that only allow electricity to flow if all or some of the transistors are on
What are some examples of logic gates?
The AND gate performs the Boolean AND function:
It will only output true if both of its inputs are true.
The OR gate performs the Boolean OR function:
It will output true if either or both of its inputs are true.
The NOT gate performs the Boolean NOT function:
It takes one input and inverts it.
What are logic circuits?
Logic gates can be combined to create complex logic circuits
These logic circuits can perform functions such as adding numbers and storing data
How do you evaluate Boolean expressions?
To evaluate a Boolean expression, you should substitute all of the values in for the variables and then use the definitions of the different Boolean functions to simplify it one step at a time.`
What is the order you should evaluate a Boolean expression?
You should evaluate any expression in brackets first, for example:
NOT(True OR False)
NOT(True)
False
What are truth tables?
Truth tables are another method of evaluating expressions
A truth table shows every possible combination of inputs and the resulting output
The truth table shows the input and output state for each combination
The table can then be used to look up the output.
What is the most common type of computer software?
Application software
What is the purpose of application software?
Application software helps a user of a computer system to complete a given task.
What are some examples of application software?
Presentation software
Word processors
Web browsers
What is the purpose of system software?
System software controls the hardware of the computer and provides an environment for applications to run
What are Operating systems?
Operating systems (OSs) are one type of system software. OSs manage access to the hardware in the computer.
What are device drivers?
Device drivers are one type of system software
Device drivers are small programs which tell the operating system how to use a piece of hardware
What is Utility software?
Utility software is one type of system software
Utility software performs maintenance tasks to make sure the operation of the system continues
What is utility software?
Utility software is a subset of system software. Utility software programs perform specific tasks to help maintain the system
What are the 4 main types of utility software?
Compression
Encryption
Backup
Defragmentation
What is compression?
Compression involves applying an algorithm to reduce the space needed to represent a file or its contents.
What is encryption?
Encryption is designed to prevent unauthorised access to files by applying an algorithm to “scramble” data
What is backup?
Backup involves making copies of data that can be restored in the event of a data loss.
What is Defragmentation?
Defragmentation involves improving hard disk performance by applying an algorithm to reorganise data.
What is the purpose of the Operating system?
An operating system (OS) is a piece of system software which controls the hardware within a computer
What is the API?
Operating systems provide an application programming interface (API)
This is a set of code libraries that software developers can use to write applications for that operating system
What are different pieces of hardware controlled by?
Each piece of hardware is controlled by a manager
What does the User Interface (UI) manager do?
The user interface (UI) manager provides the user interface which allows users to control the computer
What does the device manager do?
The device manager allocates resources to external hardware devices and allows them to be used by applications
What does the memory manager do?
The memory manager controls the allocation of memory between applications
`What does the user manager do?
The user manager authenticates and separates users of the computer
What does the process manager do?
The process manager controls the allocation of central processing unit (CPU) cycles to multiple running applications
What does the file manager do?
The file manager controls the opening, reading and writing of files in secondary storage
What does WIMP stand for
WIMP stands for window-icon-menu-pointer
What are command line interfaces?
A command line interface (CLI) is an environment where the computer is controlled by typing text commands using the keyboard.
The computer cannot display graphics, only text.
CLIs use less memory than graphical interfaces.
What are Graphic User Interfaces (GUIs)?
Graphical user interfaces (GUIs) are more modern environments to work in
GUIs are usually based on the window-icon-menu-pointer paradigm or a multi-touch interface
What is the purpose of memory manager?
The memory manager controls the allocation of random access memory (RAM) to each running process.
If the memory manager fails to manage memory well, then the computer will slow down and might crash.
What is the purpose of the process manager?
Modern operating systems allow users to run multiple programs at once.
In reality, a CPU can only execute one process at a time. So the CPU must switch between processes so quickly that it seems that they are running simultaneously.
What is multitasking?
Modern operating systems allow multiple applications to run at once. This is known as multitasking.
For this to work, the operating system must manage how memory and CPU time is allocated to each running process
What is the purpose of the device manager?
The device manager keeps track of which devices are connected to which ports
The device manager also allows applications to read or write data to each device
What are peripheral devices?
Peripheral devices are devices that the device manager manages
What are some example of peripheral devices?
Keyboard Mouse Printer Webcam Headphones Monitor
What are device drivers?
The device manager works closely with special system software called device drivers.
Device drivers contain software that tell the operating system how to understand the data coming from the device and what format it expects to receive data in.
What is the purpose of the file manager?
The file manager is responsible for setting and managing the access rights of each file.
For example, the file manager decides if a file can be Read, Modified or Executed
The file manager is also responsible for keeping track of where specific files and folders are located in secondary storage
The file manager is responsible for determining the type of a file, and sending it to the correct application
What is a single-user operating system?
A single-user operating system is an OS which supports one user at a time.
A single-user OS may or may not support multiple user accounts, although only one account may access the system at a time
What is a multi-user operating system?
A multi-user operating system allows several users to be connected at the same time
What is the purpose of the User manager?
A user manager keeps track of which users can access the system and who is currently logged in.
The user manager also handles authentication, or logging in.
The user manager is also responsible for making decisions based on access rights:
For example: Can user X access document Y?
What are files?
Files are documents or executable programs that are stored on a computer’s secondary storage
Can a single-user operating system have two user accounts?
Yes, but only one account can access the system at one time
What are all modern Central Processing Units (CPUs) are based on?
All modern Central Processing Units (CPUs) are based on Von Neumann architecture
What are the components of Von Neumann architecture?
The components of Von Neumann architecture are:
Arithmetic and Logic Unit (ALU)
Control Unit
Registers
What is the purpose of the Arithmetic and Logic unit?
The ALU performs all of the arithmetic and logical operations of the CPU, including:
Addition and subtraction, multiplication and division.
Comparisons such as whether numbers are equal or if one is greater than another
Boolean operations such as AND, OR and NOT
What is the purpose of the control unit?
Sends out control signals to other parts of the CPU.
Executes program instructions by following the fetch-decode-execute cycle.
What are the two key parts that make up the control unit?
The clock - coordinates the CPU’s activity
The decoder - decodes program instructions
What is the purpose of registers in the CPU?
Registers are tiny amounts of super-quick memory within the CPU.
They are used to hold information needed for the CPU to work
Each register holds a specific piece of information
What are Special purpose registers in the CPU?
Special purpose registers are registers that have a predetermined purpose in the central processing unit
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What is the purpose of the Program Counter (PC)?
The program counter (PC) holds the memory location address of the next instruction to be performed by the CPU
What is the purpose of the Accumulator (ACC)?
The Accumulator (ACC) holds the result of calculations and operations performed by the arithmetic logic unit (ALU)
What is the purpose of the Memory Address Register (MAR)?
The Memory Address Register (MAR) holds the address of the location in memory where data is to be retrieved or stored
What is the purpose of the Memory Data Register (MDR)?
The Memory Data Register holds the data that has been retrieved from memory, or that is about to be stored in memory
What is the Fetch, Decode, Execute (FDE) cycle?
The Fetch, decode, execute cycle is a cycle that the processor need to do to process instructions and data by retrieving them from the memory
What is Fetch in the FDE cycle?
The address of the next instruction to be processed is copied from the Program Counter (PC) to the Memory Address Register (MAR).
The PC is incremented to point to the next instruction that will be needed when the cycle starts again.
The instruction stored at the location held by the MAR is copied to the MDR
What is Decode in the FDE cycle?
The Control Unit decodes the instruction and sends control signals to the component within or outside the CPU that needs to act
What is Execute in the FDE cycle?
The operation indicated by the instruction is performed by the appropriate component
For example:
The Arithmetic Logic Unit (ALU) performs the operation given by the Control Unit
The value stored by the Program Counter or Memory Address Register might be changed
What are the factors that effect the CPU’s Performance?
Cache Type
Cores
Cache Size
Clock speed
How does cache type effect the CPU’s Performance?
Level 1 (L1) cache is the fastest, but smallest form of cache memory:
L1 cache is found inside the central processing unit.
Level 2 (L2) cache is the second fastest form of cache memory, and is larger than L1 cache:
L2 cache is usually found on a secondary chip, close to the CPU.
Level 3 (L3) cache is the third fastest, and largest form of cache memory:
L3 cache is usually found on a chip between the CPU and the main store
How does cores effect the CPU’s performance?
Each core of a CPU is capable of processing instructions independently.
Each core has its own Control Unit (CU) and Arithmetic and Logic Unit (ALU), but the cores share access to cache and main memory.
Multiple cores allows a CPU to process multiple instructions at the same time
How does cache size effect the CPU’s performance?
Cache memory is a small amount of very fast memory inside the CPU.
In comparison to the cache, accessing the Random Access Memory (RAM) is a very slow operation.
By storing frequently accessed data and instructions in cache memory we can avoid the process of accessing the RAM.
More cache memory speeds up the processor
How does clock speed effect the CPU’s performance?
The CPUs clock sends a pulse at fixed intervals to trigger the next stage of the fetch, decode, execute (FDE) cycle.
The higher the clock speed, the more pulses are sent per second, so more instructions can be executed in the same amount of time
What is Random Access Memory (RAM)?
Random Access means that any part of the memory can be accessed as quickly as any other part of the memory
What are the pros and cons of RAM?
Pros:
Fast - RAM is much faster to access than secondary storage such as Hard Disk Drives (HDDs)
Cons:
Expensive - RAM is much more expensive per unit capacity than secondary storage media
Volatile - RAM is volatile. This means that it will lose its contents when power is lost (i.e. if the computer is switched off)
What are the two main types of memory?
Random Access Memory (RAM)
Read-only Memory (ROM)
What are the Pros and Cons of ROM?
Pros:
Non-Volatile - ROM keeps its contents when power is lost.
Cons:
Read only - ROM is often made from flash memory. This means that it’s contents cannot be changed easily.
This means that the ROM only stores small programs that boot up or start up the computer
Fast but expensive - ROM is very fast to access.
ROM is expensive, so tends to be only small.
Where is ROM found?
ROM is found on a small, factory-made chip on the motherboard
What is solid state storage sometimes referred to as?
Flash storage or Flash Memory
Where does flash memory store data?
Flash memory stores the value of each bit in a semi-conductor chip
How can data be accessed in Flash memory?
Data can be accessed randomly. This means that any piece of data can be accessed in a constant amount of time.
This is achievable because there are no moving parts.
How reliable are Solid State Drives (SSDs)?
Solid state drives (SSDs) are robust. They have no moving parts, so they are not easily damaged by shocks.
SSDs have a limited number of read/write cycles. After a certain number of re-writes they will stop working
What are the pros and cons of Solid State Media?
Pros:
High Speeds - They have fast read/write times
Reliable - Robust and rarely fails
Good Capacity
Cons:
High Costs - Solid state media has a higher cost-per-GB than magnetic media
Solid state drives (SSDs) do not last as long as hard disk drives (HDDs), so the cost can often seem restrictive
What is the most common type of magnetic storage?
Hard Disk Drive
How are bits stored in magnetic storage?
Each bit (0 or 1) is represented as a positive or negative charged magnetic particle These are part of a magnetic disk called the platter
How is data accessed in magnetic storage?
Data could be stored anywhere on the disk, and so to read/write data we first need to find the location on the disk.
A magnetic read/write head is used to access the data while the platter spins
How reliable is magnetic storage?
The HDD has moving parts.
Although the HDD is generally reliable, any device with moving parts will be subject to wear-and-tear.
HDDs can also be damaged by shocks. They are not robust.
What are the pros and cons of magnetic storage?
Pros: Good Reliability High Capacity Low Cost Cons: Low Speed
Why does magnetic storage have low speed?
Magnetic media needs a high number of moving parts.
The high number of moving parts make magnetic media slow to access.
Why does magnetic storage have good reliability?
Magnetic media is reliable and tends to last for a long time.
Magnetic media is not robust, and tends to break on impact or during vibrations.
Why does magnetic data have a high capacity of data storage?
Magnetic media can store a large quantity of data in a compact way.
This makes them a popular choice for archives as well as home computers
What are some examples of Magnetic storage?
HDDs
Hybrid Drives
Magnetic tapes
What is optical storage?
Optical storage uses laser light to retrieve data from the surface of optical media. Optical storage is often used to deliver multimedia content such as video
How are bits stored in optical storage?
Each 1 or 0 (value of a bit) is represented as a microscopic hole (called a pit) or a flat surface (called a land) on the surface of the disk
How is data accessed in optical storage?
A laser is shone on the disk surface.
If the laser hits a land, it will be reflected into a sensor.
If the laser hits a pit, then it will be reflected elsewhere.
These can be used to represent our 1 and 0
What are the pros and cons of optical storage?
Pros:
Low Cost
Reliable - It is Waterproof and Shockproof
Good Capacity
Cons:
Not Robust
Low capacity per disk
Slow Access times
What are the three main types of optical storage?
Blue-Ray Disks (BD)
Compact Disk (CD)
Digital Versatile Disk (DVD)
What are the three Optical Media standards?
Read-Only Media (ROM)
Write-Once (R)
Re-writable (RW)
What is Read-Only Media?
A CD-ROM, DVD-ROM, or BD-ROM is a disk which can be read only.
The manufacturer writes the initial data, and this cannot be changed.
This is often used in content distribution so that people cannot accidentally overwrite the content.
What is Write-once media?
A CD-R, DVD-R, or BD-R is a disk which can be written once by the user at home.
Once the user has written data to the disk, they cannot overwrite it.
What is Re-Writable media?
A CD-RW, DVD-RW, or BD-RW is a disk which can be overwritten whenever the user would like to.
These are often used for backups which might need to be updated in the future
What is ‘The Cloud’?
‘The Cloud’ is a term that refers to storage, services, and applications that exist on the Internet, rather than on a local secondary storage
What is the cloud mainly used for?
Applications
File Storage and sharing
Streaming Services
Server Hosting
What is a Data Centre?
A data centre is a building which stores a large amount of data on secondary storage devices. Data is usually split up on multiple devices in a RAID configuration
What does RAID stand for?
RAID stands for Redundant Array of Inexpensive disks
What is RAID configuration>
RAID is a technique where multiple secondary storage devices can be combined together to provide a larger device. This technique can also provide error recovery
What is Error recovery?
If a drive in a RAID system fails, then there is data kept on the other drives which helps to recover lost data. This helps keep our data much safer then it would be on a local device
Where is data located on the cloud?
The end-user does not know the geographical location of the data centre where their data is stored. There is no guarantee that the data will even be kept in the same country
What are the pros of Cloud Applications?
The end user will never need to update the application as it would’ve updated on the central servers
Easy Access - Files and applications can be accessed from any Internet-connected device.
Data is regularly kept secured. There is no need to employ an IT specialist
What are the cons of Cloud Applications?
An Internet connection is required at all times
Users have no control as to how their is stored. It is more likely to get hacked compared to local data
Pricing plans can change at any time which can cause financial issues
Why might a company prefer to use cloud based applications rather than their own local software?
There is no need to employ specialist IT managers
How much data can a compact disk store?
A CD can store around 700 MB of data
How much data can a DVD store?
A DVD can store around 4.7 GB of data
How much data can Blu Ray disks store?
A Blu Ray disk can store around 25 GB of data
Virtual memory should never be used with what type of disk?
Solid State Disks
What is RAM?
RAM is an internal component that holds data and programs that are currently in use.
Which of these optical media can be written to once by a user but read many times?
CD-RW
CD-r
CD-ROM
A CD-R can be written to once by a user but read many times. A CD-RW can be written to and read many times.
Is ROM volatile and is ROM read only or write as well?
ROM is non-volatile and can only be read from. It cannot be written to.
What is a register?
A register is a small amount of high speed RAM contained within the processor.
What are the three types of bus?
Address bus
Control bus
Data bus
In Von Neumann architecture, what is stored in the main memory.
In Von Neumann architecture, data and instructions are both stored in main memory.
Which register holds the address of the next instruction to be fetched from memory?
The program counter (PC) holds the address of the next instruction to be fetched from memory. The MAR holds the address of the instruction about to be fetched from memory.
