Computer Systems (I) - Components of a Computer System Flashcards
What is a computer?
A machine that processes data
What is the purpose of a computer and why are they so beneficial?
The purpose is to take data, process it and output it – they are much more efficient than humans at certain tasks
What does a computer system consist of?
Hardware and software (working together to complete tasks)
What is hardware and what is software?
Give some examples
Hardware – physical components, e.g. CPU / motherboard / printer / monitor
Software – programs or applications that a computer system runs (e.g. an operating system / video games)
What are embedded systems?
Embedded systems are computers built into other devices, e.g. TVs / dishwashers
They are often used as control systems (monitoring / controlling machinery)
They are easier to design and cheaper / more efficient as they have a dedicated single task
What two types of computer system are there and what are their differences?
General purpose – designed to perform many tasks, e.g. a home PC
Embedded systems – designed to perform one specific function, e.g. controlling traffic lights
List some key components within a computer1
Power supply Cooling fans CPU Graphics card Optical drive RAM HDD / SSD Motherboard
What does CPU stand for and what does it do?
Central Processing Unit – processes all the data and instructions that make the system work
What are the 3 main parts to a CPU?
Control Unit (CU)
Arithmetic Logic Unit (ALU)
Cache
What is the function of the Control Unit (CU) within a CPU?
CU is in overall control of the CPU – manages fetching, decoding and execution of program instructions.
It also controls the flow of data inside and outside of the CPU
What is the function of the Arithmetic Logic Unit (ALU) within a CPU?
The ALU undertakes the calculations – additions / subtractions (and multiplications / divisions using repeated additions or subtractions)
It performs logic operations (AND / OR / NOT) and binary shifts
It also contains the accumulator register
What is the function of the Cache within a CPU?
Cache is very fast memory in the CPU (faster than RAM but slower than registers)
It stores regularly used data
There are three types: L1 (quickest but lowest capacity), L2 and L3 (slowest but greatest capacity)
What does the following show?
Von Neumann’s architecture for a CPU
CPU runs programs, stored in memory
Programs consist of instructions and data, stored in memory addresses
What are CPU registers?
Registers temporarily hold tiny bits of data needed by the CPU – they are very fast at reading / writing
What do CPU’s follow?
Fetch-Decode-Execute cycle
Describe the Von Neumann CPU design
Describe the Fetch part of the Fetch-Decode-Execute cycle
Fetch – copy memory address from Program Counter (PC) to Memory Address Register (MAR)
Copy instructions stored in the MAR to the Memory Data Registers (MDR)
Increment the PC to point to the next address of the next instruction, ready for the next cycle
Describe the Decode part of the Fetch-Decode-Execute cycle
Decode – the instruction in the Memory Data Register (MDR) is decoded by the Control Unit (CU)
The CU may then prepare for the next step, e.g. loading values into the Memory Address Register (MAR) or MDR
Describe the Execute part of the Fetch-Decode-Execute cycle
Execute – instruction is performed, e.g. load data from memory / write data to memory / perform a calculation or logic operation (using the Arithmetic and Logic Unit (ALU)) / change the address in the Program Counter (PC) or halt the program
What does RAM stand for and what are its properties?
Random Access Memory (RAM) is used as the main memory of a computer
It can be read and written to
It is volatile – temporary memory requiring power to retain the data
What does ROM stand for and what are its properties?
Read Only Memory (ROM) contains the instructions a computer needs to properly boot up
It can only be read from (though can be updated with a ‘flash’)
It is non-volatile – the memory is permanent, containing data even without power
What is virtual memory and why might it be used?
Computers have limited RAM – when full, data can be moved onto secondary storage (virtual memory)
This is a much slower process but will allow many programs or RAM intensive programs to run
What does CPU performance depend on?
Clock speed
Number of cores
Cache size
Why is clock speed a factor in CPU performance?
Clock speed is the number of instructions a single process can carry out per second (Hz)
The higher the clock speed the greater the number of instructions per second – which makes the machine faster
Why is the number of cores a factor in CPU performance?
Each core in a CPU can process data independently
The more cores, the more instructions that can occur at once
*Software needs to be designed to take advantage of multi-core systems
Why is the cache size a factor in CPU performance?
The cache is the data storage inside the CPU (faster than RAM)
A larger cache gives the CPU faster access to the data it needs to process
What is over-clocking a CPU?
CPUs running at a higher clock speed that the factory-set rate
Benefits exist, but it can be risky as the CPU can overheat causing crashing or permanent damage
What is the average CPU clock speed of a desktop computer?
Around 3.5 GHz (3.5 billion instructions per second)
Why does more RAM make a faster, smoother system?
More RAM means the system is less likely to rely on virtual memory (which is slow)
More RAM means more applications or memory intensive applications can run smoother
*This only works to a point, where other factors will limit the system
What are GPUs?
A GPU is a graphical processing unit
How do GPUs help CPUs?
GPUs are specialised circuits for handling graphics and images
They relive the processing load on the CPU
Dedicated GPUs can drastically improve performance of graphics-intensive applications
What are the two main tiers of storage and what are their characteristics?
Primary (CPU registers / cache / ROM / RAM) – volatile and fastest read/write speeds
Secondary (HDDs / SSDs / DVDs etc…) – non-volatile but much slower read/write speeds
What are the characteristics of HDDs?
HDDs – high capacity and reliable as well as portable and long lasting (but can be physically damaged due to moving parts)
What are the characteristics of SSDs?
SSDs – very fast and reliable (no moving parts) using a type of flash memory (though they are still quite expensive)
What other type of flash storages exists?
USB pen disks / memory cards (SD) though these are much slower and have shorter read/write lives
They are extremely small, so useful for increasing capacity (e.g. in a camera / phone / handheld console)
Compare the advantages of HDDs / SSDs
What three forms do optical discs come in?
Read only (-ROM)
Write once (-R)
Rewritable (-RW)
What are the benefits of optical discs?
CDs / DVDs / Blu-ray can hold 700 MB – 25 GB
Relatively low capacity but and slow read/write and poor reliability
Cheap, portable and not damaged by water or shocks (though easily scratched)
Compare the types of secondary storage
What are magnetic tapes mainly used for (and what are their properties)?
Magnetic tape has extremely large capacity (low cost per GB)
Often used for archiving large libraries, e.g. financial transactions
It is read/written sequentially
What are the main functions of an Operating System (OS)?
Operating Systems manage the hardware and run the software.
Main functions include: communication with hardware / user interface / platform to run applications / multi-tasking / file management / security and user accounts
Name some common Operating Systems
Windows, Mac OS, Linux
iOS, Android
What two types of user-interface are there?
Graphical User Interface (GUI)
Command-line Interface
What are device drivers used for?
Device drivers let the Operating System and hardware communicate with each other
What are the differences between a GUI and command-line?
GUI are easy ways for the user to interact with the computer system (visual, interactive and intuitive)
Command-line are text based and ‘harder’ to use for the average user but are less resource-heavy and can be very efficient and powerful
What GUI input methods exist?
Touchscreen (e.g. iOS / Android) use finger gestures
WIMP-based (windows / icons / menus / pointers) for systems such as Windows / Mac OS / Linux
How does the Operating System help with multi-tasking?
Multi-tasking can occur as the Operating System manages resources
OS opens necessary parts of an app to memory (and if not actively used, can remove / place in virtual memory)
OS divides CPU time for multiple apps, prioritising where necessary
How does the Operating System help with file and disk management?
Operating Systems affix file extensions (.jpg / .mp3 etc…) and deal with naming / saving / moving / editing / deleting files
Operating Systems also manage storage devices and any hierarchical structures
What is defragmentation and how can utilities help?
As files are moved / deleted / changes small gaps can appear on the disk
Over time the disk can become more fragmented, slowing down the read/write of the files
Utilities can reorganise files, putting the fragments back together
How does the Operating System help with user accounts and security?
Operating Systems can be single or multi-user
Access is granted to the system / different parts of the system
Operating Systems also incorporate security layers, e.g. passwords / pins / pin patterns / fingerprints / retina or facial scanners
Draw a fragmented hard disk and one which has undergone defragmentation
Why is defragmentation not needed for a SSD (or even recommended)?
SSDs use flash storage (no moving parts) so fragmentation doesn’t slow them down (they can access data just as quickly)
SSDs have a limited number of read/writes so defragmenting them shortens their lifespan
What is compression software?
Compression software reduces the size of files (temporarily or permanently)
Compressed files take up less space and are quicker to download
They need to be extracted (e.g. .zip and .rar)
What are the two types of compression type?
Lossless (data retained) and Lossy (data lost)
What is encryption software?
Encryption scrambles (encrypts) data so even if stolen it cannot be understood
To decrypt a key must be known – modern encryption can be extremely difficult to crack
Can encryption be cracked with ‘brute force’?
Brute force attacks can’t be used to guess keys, so modern encryption is very secure. However, it isn’t a guarantee that it can’t be broken
