Component 1 -Revision-

Component 1 -Revision-

1. 1.1 Systems Architecture

   • CPUs
     • Part of computer needed for processing data and instructions
     • Performace
       • Clock speed= no. of FDE cycles per seconds (Hz per second), increasing clock speed= faster CPU running more instructions per second
       • Cache holds commonly used instructions/data, so they can be reached quicker and the CPU runs quicker. Increasing cache size means more instructions and data can be stored so the CPU runs even quicker
       • Cores= independent processors in CPU that process instructions. Doubling cores= double the number of instructions the cores can process
     • Components
       • Program Counter- stores location of next instruction in program to be fetched
       • Memory Address Register- stores location for data to be fetched from/sent to memory
       • Memory Data Register- stores data that has been fetched from/will be sent to memory
       • Accumulator- stores result of calculation carried out by ALU
       • Current Instruction Register- stores instruction to be decoded by ALU
       • Arithmetic Logic Unit carries out arithmetic/logic operations in instruction
       • RAM/Main Memory- volatile memory that stores data and programs currently in use (not permanent- power off= lost data)
       • Control Unit- helps control the flow of data and decode instructions
       • Cache- small section of memory, stores commonly used data and instructions to increase processor speed
       • Buses- channels of communication used to transport data and instructions in the CPU
   • Embedded computer systems
     • Designed for very few, specific functions
     • Built into a machine
     • E.g. the flashlight on your phone
   • FDE cycle
     • Step 1- fetch
       • Value placed in Program Counter determines address of instruction to be carried out
       • Address passed to Memory Address Register to locate data/instruction
       • Value sent to memory to locate the address via address bus
       • Data in memory address sent to Memory Data Register via data bus
     • Step 2- decode
       • CPU uses instruction set to decode (understand) the instruction
       • Instruction set= set of commands in language CPU understands
     • Step 3- execute
       • Any actions required by the instruction take place, e.g. calculations
       • Arithmetic Logic Unit carries out calculations

2. 1.2 Memory & storage

   • RAM- Random Access Memory
     • Where all the programs and data that are currently in use are stored
     • Allows quicker access to information than other storage e.g. the hard disk
     • Volatile- all the information is lost when the computer is turned off
     • Data must be saved to a hard disk before the computer is turned off
     • Any location in the memory can be directly accessed
     • Can be read from and written to
   • ROM- Read-Only Memory
     • Computer only reads from this memory- it doesn't write to it
     • It contains the programs needed to 'boot-up' your computer
     • Non-volatile- the data is saved even after your computer is switched off
     • Very small amount of memory
     • Can only be read from
   • Virtual Memory
     • Allows the hard disk to act as an extension of the RAM
     • Used when the RAM is full
     • Unused programs are moved to free up space
   • Types of storage
     • Optical storage e.g. CD, DVD, Blu-ray
       • Uses a lens and a light beam to read/write data onto a disk
       • Portable- small and light
       • Cheap to manufacture
       • Fairly durable- safe to store data on for long periods of time
       • Some formats (e.g. CD-R and DVD-R) mean that data cannot be overwritten
       • For some (e.g. Blu-ray) a special drive is needed to read/write the data to/from a disk
       • For some (e.g. Blu-ray) a special drive is needed to read/write the data to/from a disk
       • Storage capacity is relatively small compared to other storage devices- CDs can typically hold up to 700mb of data
     • Magnetic storage e.g. hard disk drive
       • Uses magnets to record data on rotating metal plates
       • Large storage capacity
       • Fast access to read/write data
       • Fairly cheap to manufacture
       • Can suffer wear and tear due to moving parts
       • Data can be lost/altered by magnetic field or mechanical problems
     • Solid-state storage e.g. SD cards, USB memory sticks
       • Uses flash memories to store data
       • Faster boot-up- they have no moving parts so they don't have to 'warm up'
       • Large storage capacity
       • Can be made very compact in size
       • More robust (unlikely to break) than magnetic- has no moving parts
       • Expensive to manufacture
       • Has a limited amount of time data can be written to/read from (although this can be thousands or even millions)
   • Secondary storage- any storage that is not directly controlled by them CPU, e.g. CD or hard drive
   • What elements can we consider when choosing a suitable storage device?
     • Speed- the rate at which it can transfer data
     • Capacity- the amount of data we can store on the device
     • Cost- the cost of manufacture for a device
     • Reliability- whether data is stored without technical errors and is still reliable
     • Durability- the length of time the device can store data without failing or becoming damaged
     • Portability- the device is easy to carry and move around

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