theory p1

• purpose of CPU


  To process data and instructions, and to fetch and execute instructions. take an input process it and produce an output
• fetch


  fetch the information from RAM and bring info back to the cpu
• decode


  check the information and decide what has to be performed and decodes it by alu
• execute


  instruction is executed
• ALU


  performs arithmetic and logic functions in the CPU
• CU


  sends out control signals to coordinate data and also decodes instructions and runs fe cycle
• cache


  small , but very fast memory location that provides fast access to frequently used instructions , it speeds up performance as its faster than RAM and located close by
• registers


  storage locations that temporarily hold data and instructions, MDR , MAR , PC , ACC
• pc


  Holds the memory address of the next instructions to be fetched from memory , Increments by 1 as the fetch-decode-execute cycle runs
• MAR


  Holds the memory address of where data or instructions are to be fetched from, or address of where data is to be stored
• MDR


  Stores the data or instruction which has been fetched from memory or to be sent to memory
• accumulator


  Stores the results of any calculations that have taken place in the ALU
• clock speed


  number of cycles per second , a faster clock speed means more fde cycles are done at a time so more instructions are executed .
• GhZ


  billion
• cores


  each core executes an instruction , so completes a fde cycle . adding more cores allows parallel processing so instructions can be executed simultaneously
• drawbacks of cores


  some systems dont allow a multi core processor so it has no use , and if a bottleneck occurs in one core then rest of the executions have to wait so performance may not be any better
• embedded systems


  Special-purpose software built into a computer system that has limited function eg camera , fridge , washing machine
• characteristics of embedded systems


  - Low power so they can operate effectively from a small power source.

  - low cost, making them suitable for use in mass produced,

  - Dedicated software to complete a single task or limited range of tasks
• RAM characteristics


  holds applications and programs that are currently in use and tends to be quicker than secondary storage

  volatile , read and write
• ROM characteristics


  used to hold BIOS and not deleted when computer turns off

  only read , non-volatile
• need for primary storage


  Much faster than secondary storage and holds data and instructions needed by the CPU, whilst the computer is running.
• virtual memory


  a portion of a secondary storage (HDD) medium functioning as additional RAM, and it holds instructions that aren't currently in use to free up more space in ram
• drawbacks of RAM


  it can slow down the system as process of swapping data is time consuming
• why have secondary storage


  to store files and access them when power is off , they have a high storage and also tend to be cheaper
• optical storage


  uses light properties to read data from disk and do this by using moving parts

  -small capacity , small and easily moved so portable

  -not robust , easily scratched

  -small cost per Gb

  -slow access time
• magnetic HDD


  read with a moving head inside disk

  -high capacity

  -low cost , but also moving parts can get damaged so also not very portable

  -moderate access

  -make noise so
• SSD


  -portable , and its smaller and also more robust as no moving parts

  -large capacity however it is more expensive( can be reused though)

  -faster access speeds
• why must data be in binary format


  computer is built using switches and transistors that can either be on or off, this fits the binary number system which only has two digits (1/0), this means all data must be converted to binary before a computer can understand and process it
• binary


  The binary number system is base 2, using only bits 0 and 1,
• binary to denary and vice versa


  write out binary headings

  
• binary addition


  1+0=1 1+1=10 1+1+1=11

  
• overflow error


  Error that results when the number of bits assigned to a calculation has exceeded the allocated slot , as it is too big - can lead to loss of data and accuracy
• denary and hexadecimal


  base 16 - better for large values , fewer digits to represent , easier to read , less prone to errors

  
• binary shifts and their effects


  Left shift multiplies the number by 2; right shift halves the number by power of 2 . they can cause a loss of precision

  
• character set


  A list of the characters and the unique binary codes used to represent each one , they are logically ordered and are vital for computers to process and communicate characters
• character set and number of bits


  different sets have different amounts of characters , more characters means more bits needed
• ASCII


  a code for representing English characters as numbers, with each letter assigned a number from 0 to 127, it uses 7 bits and uses basic characters for english , so not many other languages
• extended ASCII


  an 8-bit character set consisting of 256 characters , it allows for more symbols
• UNICODE


  Uses a 16-bit representation for characters. and allows for many more languages to be represented , however is requires lots more storage i
• images


  made up of small pixels and each pixel has its own binary code that are unique to its colour