computing paper 1 (2)

• Function of CPU

  Fetching - searching and retrieving instructions from the memory

  
  

  Decoding - Sorting the instructions into parts for specific parts of the CPU

  
  

  Executing - The instruction is followed (to 'run')
• Register

  A component for holding short term memory, used to store addresses or data currently being worked on.
• Memory Adress Register (MAR)


  used to store the address of the next instruction / data to be accessed
• Memory Data Register (MDR)


  contains the data value being fetched or stored to main memory
• Program Counter (PC)

  used to store the address of the next instruction to be performed by the CPU
• Accumulator (ACC)


  used to store the value currently being worked on / result of the last calculation from ALU.
• What are the effects of using a processor with a faster clock speed?

  More instructions carried out per second and so instructions are executed more quickly, which allows for more programs to be run at the same time. This then allows for more complex processing (e.g. 3D graphics) to be completed in real time.
• What are the effects of using a processor with more cores?

  More instructions carried out simultaneously, the processor can process more instructions at the same time, which allows batches of instructions to be executed more quickly, which allows for more programs to be run at the same time.
• What are the effects of using a processor with a bigger cache?

  More space for frequently used instructions / data, more storage for very fast access, meaning faster fetching of instructions - so faster processing, meaning faster fetching of data - so faster processing.
• Embedded System

  A computer system that forms part of an electronic device
• What is the purpose of embedded systems?

  To provide specific, pre-defined function which is cheaper than providing a personal computer system. It doesn't include unnecessary features, can be made much smaller than a personal computer system, allows for a device to be automated / programmed.
• Examples of Embedded Systems

  Microwave Ovens

  Washer-dryers

  Car dashboards

  Calculators

  Sat-Navs

  Digital Cameras
• Purpose of ALU

  Arithmetic & logic unit, used to perform arithmetic calculations (e.g. add, subtract, multiply), used to perform logical operations (e.g. <, >, =, !=). or boolean
• Purpose of Control Unit (CU)

  Control the flow of data within the CPU (i.e. between registers), control input and output of data to/from the CPU, controls the timing of signals sent within the CPU.
• Purpose of Cache

  Stores frequently used instructions and data, built onto the CPU, provides faster access than RAM, allows instructions and data to be loaded into the CPU more quickly.
• The Fetch Stage of the Fetch, Decode, Execute Cycle

  1) The address of the next instruction to be processed is copied from the Program Counter (PC) to the Memory Adress Register (MAR)

  
  

  2) The PC is incremented to point to the next instruction that will be needed when the cycle starts again

  
  

  3) The instruction stored at the location held by the MAR is copied to the MDR.
• two items that are stored in RAM.

  Programs currently in use.

  Data currently in use.
• Main difference between RAM and ROM

  RAM is volatile

  ROM is not volatile

  ROM read only

  RAM is not read only
• Role of POST (power on self test) in the boot sequence


  When the computer is switched on, BIOS chip performs checks (Called POST)

  To make sure components are present and functioning correctly/ Checks peripheral devices, other hardware, storage devices, memory and system clock. When checks complete CPU starts operating system. If a test fails, an error message is shown.
• reasons ROM is considered permanent and secure?

  Security against accidental/malicious damage as difficult to change

  Virus attack unlikely

  Manufactured with data required permanently stored in it so cannot be modified easily.
• What is virtual memory?

  A technique that uses a portion of the computer's hard disk (secondary storage) as an extension of RAM
• Why is virtual memory needed?

  When you need to run applications on the computer than its physical memory (RAM) can support.

  It lets more memory to be used than there is in the system.
• How is virtual memory implemented?

  Divide program into pages

  
  

  Divde memory into frames

  
  

  Using a page table as a translation mechanism

  
  

  Using the TLB to reduce memory accesses thus speeding up the process

  
  

  Using the hard drive by bringing pages into memory on demand
• Define TLB

  A translation lookaside buffer (TLB) is a memory cache that is used to reduce the time taken to access a user memory location. It is a part of the chip's memory-management unit (MMU). The TLB stores the recent translations of virtual memory to physical memory and can be called an address-translation cache.
• What does solid state media mean?

  Storage media with no moving parts

  Refers to removable storage with no moving parts

  Device that uses flash memory
• Uses for flash memory

  USB drives

  Memory cards (SD cards)

  Solid-state drives
• Advantages of flash memory

  (Advantages of Solid state)

  Robust/ durable

  Very relaible as no moving parts

  Compact but can store lots of data in a small space

  Very fast access time compared to hard disk or a DVD

  Cheap

  Light weight (very portable)
• Disadvantages of flash memory

  Can get lost easily

  Relatively short life span

  Cost > CD or DVD

  Metal part of USB's can be damaged
• Define secondary storage

  Storage where devices are not constantly connected to the computer.

  Devices which are not directly accessible by the computer's CPU
• Use of secondary storage

  Used to back up data stored in main memory/primary storage.

  Stores programs/data and other files that would otherwise be lost when the power is switched off

  Need for larger storage capacity.
• Other name for secondary storage

  Auxiliary (storage)
• Examples of external secondary storage devices.

  CDs

  Memory card (SD cards)

  DVD

  Blu-ray disc

  Flash drive

  USB memory stick

  External hard disk drive

  External solid state drive
• Examples of internal secondary storage devices

  Hard disk drive (HDD)

  Solid state drive (SSD)
• Types of secondary storage

  Optical

  Magnetic

  Solid state (Flash)
• Advantages of optical storage

  Cheap, easy to transport, relaible, robust, relatively large capacity.
• Advantages of magnetic storage

  Large storage capacity, low cost (cost-effective) Commonly used making it possible to share compatibility

  Often used to store OS.
• Advantages of secondary storage

  Non-volatile

  Stores large amount of data
• Disadvantage of secondary storage

  Data may be outdated

  Device could get lost

  Need for a writer on the computer to write infomation to CD, DVD, Blu-ray discs.
• reasons why a CD-ROM is suitable for distributing music

  Cheap to produce.

  Easily portable.

  Enough capacity for the music tracks.

  Can be read by other devices.

  Read only/can't be over written.
• Disadvantages of magnetic tape

  Slow to write to and read from memory.

  All data has to be read before reading the data you want.

  Data could be corrupted if close enough to a magnetic field.

  Additional equipment needed to read data from tape.