computer systems Flashcards
what is a computer?
a machine that processes data
what does a computer system consist of?
hardware and software
hardware?
physical stuff : motherboard, monitor
software?
the programs that a computer system runs : video game, operating system
what is an embedded system?
computers built into other devices with a single, dedicated task
embedded system examples?
washing machine, dishwasher, windscreen wipers
expand on embedded system dishwasher example?
the embedded system could control the water pumps and water release mechanisms, manage the various dishwasher cycles and control the thermostat to keep water at an appropriate temperature
why are embedded systems better than a computer?
theyre dedicated to a single task so they are:
cheaper
more efficient
easier to design
CPU stands for?
central processing unit
what does the CPU do?
it processes all the data and instructions that make the system work
what are the 3 main parts of the CPU?
control unit (CU)
arithmetic logic unit (ALU)
the cache
what is the control unit?
overall control of the CPU
fetch decode execute cycle
controls the flow of data
what is the arithmetic logic unit?
performs all the calculations
what is the cache?
stores regularly used data for the CPU to access quickly
characteristics of cache?
very fast memory
low capacity
expencive
what else does the CPU contain?
registers
what do registers do?
temporarily hold tiny bits of data needed by the CPU
characteristic of registers?
super quick to read/write to
example of registers?
MAR - memory address register
MDR - memory data register
ACC - accumulator
PC - program counter
what is the program counter? (PC)
holds the memory address of the instruction for each cycle
what is the accumulator? (ACC)
stores results of calculations from the ALU
what is the memory address register? (MAR)
holds any memory address about to be used by the CPU
the address might point to data or a CPU instruction
what is the memory data register? (MDR)
holds the actual data or instruction that has been fetched from memory or waiting to be written to memory
who is von neumann?
came up with a CPU design where it runs programs stored in memory
describes how most computers work today
made in 1945
what cycle does the CPU follow?
fetch - decode - execute
what is fetch?
copy memory address from the PC to the MAR
copy the instruction stored in the MAR address to the MDR
increment the PC to point to the address of the next instruction for the next cycle
what is decode?
instruction in the MDR is decoded by the CU
what is execute?
the instruction is performed/outputted
why is the FDE cycle important?
to run instructions efficiently
what is memory?
storage of all the instructions that the CPU follows
what does RAM stand for?
random access memory
what is RAM?
the main memory in a computer where all files, data and programs are stored while being used
can be read and written to
volatile
volatile meaning?
temporary memory which required power to keep its data
forgets
non volatile meaning?
permanent memory which keeps its contents even when there is no power
doesnt forget
how does RAM work?
when a computer boots up the operating system is copied from secondary storage to RAM
when software applications are opened they are copied from secondary storage to RAM until closed
speed of RAM compared to cache and secondary storage
slower than cache, faster than secondary storage
what is virtual memory?
a secondary storage used as extra RAM
why is virtual memory used?
computers have a limited amount of RAM
when RAM is full it moves data that hasnt been used recently to virtual memory
what happens is the CPU needs to read data from virtual memory?
it moves data back to RAM
this is a slow process as data transfer rates are slow on secondary storage
what does ROM stand for?
read only memory
what is ROM?
it can only be read not written to
non-volatile
what does ROM do?
contains all the instructions a computer needs to boot up (BIOS)
when the computer is powered on CPU reads instructions from ROM to perform self checks and set itself up
what three things effect CPU performance?
clock speed
number of cores
cache size
what is clock speed?
number of instructions a single processor core can carry out per second
measured in Hz
higher clock speed = ?
greater number of instructions that can be carried out per second
what is a core?
each core in the CPU processes data independently from the rest
higher number of cores = ?
the more instructions that can be carried out at once
what is the cache?
data storage in the CPU
faster than RAM
larger CPU cache = ?
gives the CPU faster access to more data
more RAM = ?
more applications it can smoothly run making it faster
less RAM = ?
runs slowly due to use of virtual memory
what does GPU stand for?
graphics processing units
what is a GPU?
specialised circuit for handling graphic anf image processing
why are GPU’s good?
relieve the processing load on the CPU freeing it to do other things
what are the two main tiers of storage?
primary storage
secondary storage
what is primary storage?
memory areas the CPU can access quickly
primary storage examples?
RAM
ROM
cache
what is secondary storage?
where all data is stored when not in use
non volatile
read/write is much slower
secondary storage examples?
magnetic drives
solid state drives
CDs
what is a hard drive?
the traditional internal storage
- made up of a stack of magnetised metal disks that spin extremely fast
- data is stored magnetically on the disk’s circular tracks
- a moving arm accesses these areas to read or write data
advantages of hard disk drives
portable
long lasting
reliable
cheap
disadvantages of hard disk drives?
could be damaged if dropped
slower than SSD
what is a solid state drive? (SSD)
storage device with no moving parts used for internal storage
uses flash memory
advantages of solid state drives? (SSD)
has much faster read/write times than hard drives
non volatile
what is an optical disc?
secondary storage
uses a laser to read the data from pits and lands as the disc spins
examples of optical disc?
CDs
DVDs
disadvantages of optical discs?
can only be written to once
declining as streaming becomes popular
easily scratched
advantages of optical discs?
cheap
portable
what does an operating system do?
- communicate with hardware via device drivers
- provides a user interface (allows you to interact with the computer)
- allows computer to multitask
- deals with file management and disk defragmentation
what is an operating system?
runs and maintains a computer system
what is a device driver?
used to communicate with hardware
examples of device drivers?
mouse
keyboard
what is a user interface?
allows the user to interact with a computer system
what is file management?
organisation of data into a usable hierarchical structure
examples of file management?
naming
saving
moving
editing
detetion
of data
what is user management?
who can use the computer at one time
what is single user?
one user using the computer at once
what is multi user?
multiple users using the computer at once
what is utility software?
helps maintain the computer
installed within an operating system
what is defragmentation?
reorganises data to put broken up files back together
moves free space together to prevent further fragmentation
why does defragmentation exist?
disk management moves, deletes and changes sizes of files causing extra space, so the operating system fills thr gaps by splitting files
this makes it slower to read/write as it has to move back and forth
what is compression software?
reduces file sizes by either permanently or temporarily removing unwanted data so they are quicker to downloads
