Unit 1 - Computer Components Flashcards
define control unit
-the part of the CPU that manages the execution of instructions. it fetches, decodes and synchronises instructions before executing it by sending control signals via the control bus to other parts of the computer
define buses
a common physical pathway shared by signals to and from several components of a computer
define ALU
arithmetic logic unit - where data is processed and manipulated by performing arithmetic, logic and shift operations allowing a program to make decisions
define accumulator
holds all inputs/outputs, holds results of any calculations, checked for conditional branching, stores data from the MDR/RAM
define CPU
central processing unit - the main part of the computer, consisting of the registers, ALU and CU
- processes instructions and runs the OS
name the 5 main registers
- PC
- CIR
- MAR
- MDR
- ACC
function of the program counter
holds the memory address of the next instruction to be executed
function of CIR
current instruction register - holds the address of the current instruction being executed and decoded, which is split into opcode and operand
function of MAR
memory address register - holds the address of the memory location currently in use
fetch - address of the instruction being loaded
execute - address of the data being used
function of MDR
memory data register - acts as a buffer by temporarily holds data moving between the processor and main memory
steps in the fetch stage of the FDE cycle
- address of instruction moved from PC to MAR
- data/ instruction held at the address is moved to MDR
- PC incremented by 1
- contents of MDR moved to CIR
steps in the decode stage of the FDE cycle
- instruction in CIR decoded
- split into operand and opcode to determine the type of instruction. (additional data fetched if required)
- passed to the ACC
steps in the execute stage of the FDE cycle
- the instruction is executed and result held in ACC or stored in memory
what is the opcode
specifies the operation to be carried out
what is the operand
holds either:
- the address of the data to be used, which is then copied to the MAR
- the actual data to be operated on, which is passed to the MDR
define words
sections of memory that each hold a seperate memory address
function of the address bus
the part of the bus which carries identification about where data is being sent
- the width of the address bus determines the maximum possible memory addresses of the system
function of the data bus
the part of the bus that carries the actual information
- bi-directional so data can be sent both ways along the bus. the width of the data bus is defined by the number of wires or lines it contains.
what determines machine code format
architecture of the computer
- including word size and bus width
what are three factors affecting performance
- clock speed
- number of cores
- amount and level of cache
how does clock speed affect processor perfomance
FDE cycle is triggered by the clock pulses from the system clock the faster the clock speed the greater number of cycles per minute
how does the number of cores affect processor performance
each core is theoretically able to process a different instruction at the same time with its own FDE cycle, making a quad core computer up to four times faster than a single core processor
why might an increased number of cores not affect processor performance
the software may not be able to take full advantage of all multiple processors
define parallel processing
using several processor cores working at the same time
advantage of parallel processing
if the system is designed for parallel processing, each core can work concurrently on different parts of the same time therefore reducing time taken to complete
why does the amount and type of cache affect processor performance
the more and higher level cache memory a computer has, the more likely it is that it will not have to fetch the next instruction or data from RAM, as it will already have been loaded into the super fast cache memory from which it can be retrieved more easily
define cache
a small amount of super fast memory between the central processor and main memory that stores data and instructions that have recently to take advantage of its short fetch cycle
why does the location of the cache affect processing performance
cache is located on the cpu and therefore it takes less time to fetch instructions/data and copy them to the corresponding registers
factors of level 1 cache
- memory split into instruction cache and data cache, so that data and instructions can be fetched simultaneously
- extremely fast
- very small
- 2 - 256KB
factors of level 2 cache
- very fast but slower than level 1
- 290KB - 8MB
factors of level 3 cache
- slowest but still faster than RAM
- shared between all cores on the processor
- 4MB - 50 MB
define pipelining
an instruction can be fetched as the previous one is being decoded and the one before that is being executed
- successive steps of an instruction sequence are executed in turn by a sequence of cores able to operate concurrently, so that another instruction can be begun before the previous one is finished
define input devices
transfers data from the source in the outside world to a computer
- some require greater human intervention to generate the data
examples of manual input devices
- keyboards
- pointing devices (mouse)
- microphones
- touch screens
what are the two types of bar codes
- universal product code
- code 128
uses of 3-D scanners
- face recognition
- industrial and medical fields
define sensors
a hardware device that can take measurements of physical properties such as temperature or pressure from real world surroundings. these measurements are usually a representation of the actual property being measured
how can input devices be controlled
the output from a computer or microprocessor can alter how the process is operating - it can change the value of the next input recieved
how can input devices be monitored
the computer or microprocessor will make no changes to the process but will report the values
how can input devices be monitored
the computer or microprocessor will make no changes to the process but will report the values
define output devices
takes data produced by a computer and turns it into a human-readable form such as a printed document or an image on the screen
examples of output devices
- inkjet printers
- laser printers
- dot matrix printers
- 3D printers
applications of output devices
- medicine - with manufacturing prosthetic limbs, reconstructive surgery, general surgery
- manufacturing and art - car parts, prototyping and design, fashion and art, saving huge costs
describe the stored program concept
a program must be loaded into main memory to be executed by the processor. the instructions are fetched one at a time, decoded and executed sequentially by the processor. the sequence of instructions can only be changed by a conditional or unconditional jump instruction.
describe von neuman architecture
a single CU manages program control flow following a linear sequence of FDE. instructions and data are stored in a common main memory and transferred using a single shared bus
advantages of von neuman architecture
- owing primarily to cost and programming complexity, almost all general purpose computers are based on von Neumann’s principles
- it simplifies the design of the Control Unit
- data from the memory and from devices are accessed in the same way
describe harvard architecture
a computer architecture with physically separate storage and signal pathways (buses) for instructions and data. data storage entirely contained within the CPU, and provides no access to instruction storage as data
advantages of harvard architecture
- different sized memories and word lengths can be used for data and instructions
- harvard principles are used with specialist embedded systems and digital signal processing, where speed takes priority over the complexities of design
- program instructions and data are no longer competing for the same bus
uses of von neuman architecture
used in PCs, laptops, servers and high performance computers
uses of harvard architecture
used in digital signal processing, microcontrollers and in embedded systems such as microwave ovens and watches
differences in control unit of von neuman and harvard
von neuman - one bus is simpler for control unit design
harvard - control unit for two buses is more complicated and expensive
differences in programs for von neuman and harvard
von neuman - can be optimised in size
harvard - tend to be large
describe contemporary processor architecture
von neuman - one main memory holds data and instructions
harvard - cache is split into separate memory for data and instructions
describe CISC architecture
complex instruction set computers - a design that produces a complicated and expensive integrated circuit capable of performing a large variety of complex instructions that can be executed with several machine cycles
- enhancing CPU speed by minimizing the number of instructions per program
- von neuman architecture
advantages of CISC
- quicker to code programs
- the compiler has very little work to do translate a high-level language statement into machine code
- because the code is relatively short, very little RAM is required to store instructions
describe RISC architecure
reduced instruction set computers - a design that produces a simple, cheap integrated circuit with a basic range of machine instructions. relies on speed as it only uses simple instructions, each taking one clock cycle to be executed
- the number of cycles an instruction may take to execute is minimized
- harvard architercture
advantages of RISC
- the hardware is simpler to build with fewer circuits needed for carrying out complex instructions
- because each instruction takes the same amount of time, i.e. one clock cycle, pipelining is possible
- the logic of RISC machines is simple to decode. Consequently, fewer transistors are required to complete tasks
describe multi-core processors
able to distribute workload across multiple processor cores, thus achieving significantly higher performance by performing several tasks in parallel. these are therefore known as parallel systems
describe co-processors
is an extra processor used to supplement the functions of the primary processor. it may be used to perform floating point arithmetic, graphics processing and digital signal processing
describe the GPU
graphics processing unit - graphics processing unit is a specialised electronic circuit designed to rapidly manipulate and alter memory to accelerate computer graphics and image processing. it consists of thousands of small efficient cores designed for parallel processing.
define RAM
Random Access Memory – data, information and applications is that are currently being used are stored in the RAM. RAM is volatile so once the computer loses power the data and information will be lost
define ROM
Read Only Memory – stores the BIOS* in the ROM. ROM is non-volatile so will not lose data if the computer is turned off
- cannot be written to
define virtual memory and the need for it
virtual memory is an area of secondary storage and is used when the RAM is full so it can transfer some of the data into it
advantages of virtual memory
- uses cheap secondary storage on the hard drive
- prevents error messages saying “out of memory” - the programs and files will still open
- improved reliability and performance
- the flexibility to scale the storage requirements up and down as your needs change over time
disadvantages of virtual memory
accessing virtual memory is very slow
- TO access data, the existing data in RAM needs to be copied to the virtual memory, then data in virtual memory needs to be copied in RAM
features of secondary storage
- non-volatile
- external or internal
name the three storage methods
- magnetic
- optical
- solid state
what are 6 characteristics of storage
- capacity
- speed
- durability
- reliability
- portability
- cost
basic features of magnetic storage
disk contains concentric circles called tracks. each track is divided into sectors. disk heads mounted on mechanical arms read and write the data.
- a disk with a solid platter is a ‘hard’ disk. Soft plastic disks are known as ‘floppy’ disks.
advantages of magnetic storage
- cheap
- large storage capacity
- relatively fast write speed
disadvantages of magnetic storage
- lots of mechanical parts = durability issue
- not very portable
uses of magnetic storage
- personal computers
- storage of large quantities of data
capacity of magnetic storage
500 GB – 12TB or greater
basic features of optical storage
data is stored as pits and lands burnt or pressed into a spiral track circulating outwards from the centre. a laser beam passes over the pits and lands the level of reflection is measured. from this signal, 0s and 1s can be derived
advantages of optical storage
- cheapest
- portable – physically small
disadvantages of optical storage
- less storage capacity compared to others
- easily damaged/ scratched
- slow write speeds
uses of optical storage
- songs, videos and other multi-media storage
- backup and archiving of data
capacity of optical storage
CD-ROM – up ton 720MB
DVD – up to 8.4GB
Blu-Ray – up to 50GB
basic features of solid state storage
flash memory:
large electric current used to force electrons through a barrier and trap them on the other side. they remain on the other side until “flashed” with a new current, hence the name – trapped (charged) or not trapped = 0 or 1
advantages of solid state storage
- highly durable
- very fast read/write speeds
- no noisy fan or drive arm
- faster start up times
disadvantages of solid state storage
- more expensive per GB than magnetic hard disks
- lifetime issues as flash memory degrades
uses of solid state storage
- higher end computers
- laptops
- smartphones and tablets
examples: USB Pen drives, SD cards, micro SD cards, SIM card
capacity of solid state storage
100GB – 16TB
define GPU
graphics processing unit capable of rendering graphics for display on an electronic device
how does a GPU work
it gets instructions from the CPU and uses parallel processing and specialized RAM to handle graphics information
differences between CPU and GPU
- CPU needs/requires more memory
- GPU is generally faster
- CPU contains a smaller amount of more powerful cores
- GPU is suitable for parallel processing
- CPU emphasis on low latency; GPU emphasis on high throughput
other uses of a GPU
- video editing
- 3D rendering
- scientific computing
- improving the video editing process
disadvantage of RISC
RISC processors use simpler instruction sets, complex and high-level instructions need to be divided into multiple, simple instructions - as a result, software components have more work to do in RISC than the processor’s hardware - can lead to compiler malfunction
define concurrent processing
when more than one process is running from a program at once, with each process in turn being given a slice of an available processor’s time
define virtual storage
data stored on a remote hard disk accessed over the internet
