1.1/1.2 Flashcards
what is a computer?
an electronic device which takes input, processes data and delivers output
what is the purpose of the cpu?
To fetch, decode and execute instructions
what happens at the ‘fetch’ stage in the fetch-execute cycle?
fetches the next instruction from the main memory (RAM). Brings the instruction back into the cpu.
what happens at the ‘decode’ stage in the fetch-execute cycle?
inspects the instruction and works out what it is that needs doing.
what happens at the ‘execute’ stage in the fetch-execute cycle?
carries out the instruction (e.g going back to main memory and grabbing some data,performing a calculation , storing info back into main memory)
what are the common cpu components
arithmetic logic unit (ALU) , control unit (CU) , cache , registers
what is the purpose of the ALU?
performs calculations and logical decisions
what is the purpose of the CU?
sends signals to control how data moves around the CPU
what is the purpose of the cache?
provides fast access to frequently used instructions and data
what is the purpose of registers?
tiny,super fast pieces of onboard memory inside the CPU each with a very specific purpose
what does the Von Neuman architecture consists of?
control unit (cu) , arithmetic logic unit (alu) , memory unit (typically ram) , inputs and outputs.
what are the names of registers in the Von Neuman architecture?
program counter (pc) , memory address register (mar) , memory data register (mdr) , accumulator
what is the purpose of the program counter?(register)
holds the address of the next instruction in memory
what is the purpose of the memory address register?(register)
holds the address of where data is to be fetched or stored
what is the purpose of the memory data register?(register)
holds the data fetched from or to be written to memory
what is the purpose of the accumulator?
holds the result of calculations
what factors affect cpu’s performance?
Clock speed, Cache size, Number of cores
how does ‘clock speed’ affect the cpu’s performance?
the more pulses per second the more fetch-decode-execute cycles.
how does ‘cache size’ affect the cpu’s performance?
the bigger the cache the less time a processor has to wait for instructions to be fetched.
how does the ‘number of cores’ affect the cpu’s performance?
(each core is capable of fetching, decoding and executing its own instruction) More cores a cpu has the greater the number of instructions it can process in a given space of time.
what is a cpu called with 2 cores?
dual core
what is a cpu called with 4 cores?
quad core
how could dual core affect performance?
a program is split into two or more parts and each part is processed at the same time) In theory this would double performance on a dual core cpu as each part is processed independently. (however, you do not always get twice the performance because many programs cannot be split neatly into two independent parts).
What is an embedded system?
a computer system that is built into another device
what are the characteristics of an embedded system?
low power consumption , small size , rugged operating ranges , low cost per unit .
what are examples of an embedded system?
traffic lights,
factory equipment
hospital equipment
why do computers need primary storage?
holds the data and instructions which the CPU needs access to while a computer is running ,
the CPU = quickly access data fronts primary storage
what does the primary storage consist of?
random access memory (RAM) , read-only memory (ROM) , registers and cache
what is the purpose of RAM?
holds the operating system, programs and data in use by the CPU when the computer is running.
what is the purpose of ROM?
holds the first instruction for when the computer is first turned on (known as bootstrap)
what are the characteristics of RAM?
volatile (contents lost when the power is turned off)
read and write
large
what are the characteristics of ROM?
non-volatile (contents remain when power is turned off)
read only
small in comparison to RAM
why might virtual memory be needed in a system?
virtual memory is needed when there is not physical RAM to store the open programs (virtual memory is held on the hard disk)
how does virtual memory work?
programs are transferred out to virtual memory from the RAM when they are not currently being executed .
programs are transferred back to RAM from virtual memory when they are needed.
why do computers need secondary storage?
to keep programs and data indefinitely.
what is secondary storage needed for?
-Storage of programs and data when the power is turned off.
-Semi-permanent storage of data that can change
-Backup of data files
-Archive data files
what are the common types of storage?
optical (CD-R/RW , DVD-R/RW , Blu-ray)
Magnetic ( Hard disk drive , tape)
Solid - state (SSD , Memory sticks , Flash memory , memory cards)
what are the features of optical storage?
low capacity , compared to other types of storage
slow to access data
thin , lightweight and portable
what are the features of magnetic storage?
high storage capacity
quick to access data
has moving parts which eventually fail
hard disks perform better if they are defragmented
what are the features of solid state storage?
medium storage capacity
very quick to access data
no moving parts , very reliable
no noise
low power
no need to de-fragment
limited number of read/write cycles
expensive compared to others
what is optical storage suitable for?
Read only data distribution on a large scale and small capacity situations
what is magnetic storage suitable for?
when high data capacity is required , fast access to data , low cost situations and cloud storage on server forms
what is solid state storage suitable for?
low power , small embedded system
rugged applications :portable devices
small to medium data capacity requirements
silent operation
very fast access to data
situations where the devices need to be small and lightweight
what are the advantages/disadvantages of optical storage?
advantages - cheap , lightweight , portable
disadvantages - slow access times , prone to scratches
what are the advantages /disadvantages of magnetic storage?
advantages - cheap , large capacity
disadvantages - slow access times , fragile
what are the advantages/disadvantages of solid state storage?
advantages - durable , fast access times
disadvantages - cost , limited read/writes
why does data have to be stored in binary form?
All data that we want a computer to process needs to be converted into this binary format.
What is a bit?
A binary digit, a 0 or a 1.
what is a nibble?
4 bits
what is a byte?
8 bits
what is a kilobyte?
1000 bytes or 1KB
What is a megabyte?
1000 kilobytes
what is a gigabyte
1000 megabytes
what is a terabyte?
1000 gigabytes
What is a petabyte?
1000 terabytes
what is a character set?
A defined list of characters recognised by the computer.
how is a character set represented?
by a unique binary number
what are the well known character sets
ascii
extended ascii
unicode
What is ASCII?
7 bit code that can hold 128 characters
What is extended ASCII?
8 bit code that can hold 256 characters
What is Unicode?
16 bit code that can hold 65,536 characters
how can images be stored?
in binary as bitmaps or vectors
What is encoding?
process of converting data into a binary code so that a computer can process it.
what is a bitmap image?
an image made of pixels
what is a vector image?
An image made with mathematical formulas
How is each pixel stored?
in binary
how many possible values does 1 bit have?
2 possible values: 0 and 1 , therefore 1 bit can store 2 colours: black and white
how many possible values does 2 bit have?
4 possible values: 00,01,10,11 , therefore 2 bit can store 4 colours
how do you calculate number of colours?
2n (2 to the power of n ( where n is the number of bits per pixel))
what is colour depth?
Number of bits per pixel
what is metadata?
Additional data stored with the image to define the width, height, bit depth and colour palette
how can resolution and colour depth effect file size?
the greater the resolution and colour depth the larger file size.
how many bits does a photograph have?
photograph is stored in 24bit colour depth , each pixel is 24 bits , this is 2 to the power of 24 = over 16 million colours
why is analogue sound converted to digital?
so it can be stored in binary
what is sound file size?
total number of bits in a sound
how do you calculate sound file size?
(number of samples per sec) x (number of bits per sec) x (length of sample in secs)
What is bit depth in sound?
number of bits stored per sample
how can bit depth affect sound?
the higher the number of bits the greater the quality of the sound and the larger the file size
what is sample rate?
the number of samples stored in per second
how can sample rate affect sound?
the higher the number of samples per sec , the higher the quality of the sound and the larger the file size
