Unit 1 - Computer Systems and Architecture

• Clock speed measures how many cycles the CPU does per second. It is measured in hertz
• Cache is memory on the CPU which is faster than RAM but slower than registers. It is for storing a small amount of fast accessed memory
• The arithmetic logic unit (ALU) performs arithmetic and logic operations
• Registers

  Program counter - holds the address of the next instruction to be fetched from memory, increases the value by one and is incremented after the next instruction is fetched

  Memory address register - holds the address of the current instruction that is to be fetched from memory

  Memory data register - holds the contents found at the address held in the MAR

  Accumulator - holds data for the arithmetic operations
• RAM is memory that can be read and changed in any order, used for storing data and machine code currently in use and its memory is wiped upon turning off - it's volatile
• ROM - read only memory, meaning it can be read from in any order but not written to
• Virtual memory - memory that is taken from the hard drive to store data that the RAM can't from it being full
• An embedded system is a computer system which is built into another device
• RAM can hold clipboard data
• When the RAM is no longer full, old instructions that are needed are swapped back
• Computers need secondary storage because RAM is volatile, meaning it loses its contents when the computer is switched off.
• The purpose of the CPU is to process data and instructions by constantly repeating the fetch, execute cycle
• A register is a small amount of fast access memory inside the processor where data or instructions can be stored temporarily
• Control unit

  • Sends out control signals to other parts of the CPU
  • Executes program instructions following the fetch, decode, execute cycle
  • Made up of two parts:
  • The clock - coordinates the CPU's activity
  • The decoder - decodes program instructions
• The main factors which affect CPU performance are:

  • Clock speed
  • Cache size
  • Number of cores
• Why does cache size affect the performance of the CPU?

  • Data is transferred faster
  • Which makes the CPU more efficient
  • It is faster to transfer to and from cache than to and from RAM
• The three common types of secondary storage are:

  • Magnetic
  • Optical
  • Solid state
• Characteristics to consider when choosing a secondary storage device:

  • Capacity / size / storage
  • Speed
  • Durability
  • Cost
  • Reliability
  • Portability
• An output device is a hardware device used to receive data or information from a computer system
• Which register always holds the address of the next instruction?

  Program Counter
• What is the name of the component that connects the processor to main memory?

  System bus
• In the fetch-decode-execute cycle, the control unit breaks down the instruction
• An advantage of hard disk over solid state memory is that before it fails, you get detectable anomalies
• Magnetic storage is secondary storage that uses magnetic fields to magnetise spinning metal disks to store data.

  An example is a hard disk drive or a floppy disk
• The 4 registers in the CPU are:

  Program Counter

  Memory Address Register

  Memory Data Register

  Accumulator
• Registers are tiny areas of extremely fast memory located in the CPU that are designed for a specific purpose, where data or control information is stored temporarily to enable the fetch-decode-execute cycle to operate
• A core is a processing unit within the CPU
• Optical storage makes use of a laser to shine and reflect light to read the data stored. Examples include: CDs. DVDs.
• Virtual memory is needed because the computer cannot multi-task when it runs out of memory. Virtual memory allows the system to use a portion of secondary storage as if it were additional RAM, enabling the computer to handle more tasks simultaneously even when the physical RAM is fully utilized
• The purpose of RAM is to be. a temporary store for instructions and data
• The type of storage of hard disk is secondary storage
• Hard disk drives are cheaper than solid state drives
• The purpose of the program counter is to hold the address of the next instruction
• RAM is primary storage
• ROM is primary storage
• Cache is primary storage
• Without primary storage, the computer wouldn't be able to start up or work
• Secondary storage stores the operating system of the device
• The purpose of the CPU is to:

  • Perform the fetch, decode, execute cycle
  • Process instructions
• Single core means that there is only one processor