3 Memory

• Primary memory


  • Directly accessed by CPU to execute
  • Stores temporary/currently in use data (needed to improve comp's performance/for immediate use, executed)
  • e.g instructions, programs, data to boot system
  • Smaller capacity vs secondary memory
  • Faster access speed -> system speed
  • OS loads process into primary memory
• RAM


  • To store instructions that are currently in use
  • Volatile: data is lost when powered off
  • Read-write: data can be read to or written to
  • Random access: memory locations (each with a memory address) be accessed in any order
• ROM


  • To store firmware/bootup instructions - needed for comp to run
  • Non-volatile: data is kept when powered off
  • Read-only: data can't be changed
• Cache memory


  • Type of storage
  • Holds frequently used data and instructions
  • Faster access (process) as faster than RAM
• Secondary memory


  • Not directly accessed by CPU
  • Needed for long-term permanent storage of data
  • Users' files/os/application software
  • Nonvolatile
  • Read/write - can be changed
  • Store data not currently required by CPU
  • Store data to transfer to another comp
• Magnetic storage


  • Stored on platters divided into tracks and sectors
  • Platter spun
  • Read/write arm that moves across media
  • Read/write data use electromagnets
  • Use magnetic fields to control magnetic dots of data
  • Magnetic field determines binary value
• Pros of magnetic storage


  • Huge capacity - measured in Tb
  • Cheapest cost per gb(unit of data)
  • HDD fast access speed
  • Longevity/reliable - a lot read/write cycles
• Cons of magnetic storage

  • Not as portable - HDD is built in and has moving parts
  • Magnetic fields can damage stored data
  • Data read/write not as fast as flash technology
• Optical storage


  • Uses red lasers to create and read pits and lands (stores data)
  • Sequence of pits and lands form a set of binary values
  • Spun to be read
• Pros of optical storage

  • Cheap at small capacity
  • Immune to magnetic fields
  • Portable
• Cons of optical storage

  • Not cheap if terabytes need to be stored
  • Not durable - disks can be easily scratched
  • Slow access and write speeds
• Solid state storage


  • Uses NAND/NOR tech
  • Transistors in grid are used as control gates and floating gates; to control flow of electrons thru transistors
  • When data stored, transistor's data convert from 1 <-> 0
  • Uses flash memory; data is flashed onto silicon chips
  • Writes and reads sequentially
• Pros of solid state storage

  • Portable
  • Robust - no moving parts
  • Faster to access/read/write data vs magnetic hard disk
  • Use less power - less heat/noise
• Cons of solid state storage

  • Expensive compared to HDD
  • Limited number of erase/write cycles
• Cloud storage


  • Stored in collection of servers accessed remotely(opposed to storing data locally)
  • Data owned by third party and accessed over internet
  • Physical servers and storage are needed to store data in cloud storage
• Pros of cloud storage

  • Safely backed up at remote location in case of fire
  • Access data anywhere - remote work
  • Increase storage easily without buying new hardware
  • The service manages backups, security, maintenance -company dont need to do this
  • No need to house hardware - save space costs
• Cons of cloud storage

  • Need reliable internet connection - otherwise cant access
  • Hardware maintain by third-party - company not responsible for security
  • Data is lost/unavailable if don't pay cloud storage service
  • Risk of cyberattack - another third party can access your data over internet
  • Ongoing fee
• Virtual memory


  • Free up room in RAM, allow more apps to run
  • Swapping: use secondary storage as temp primary memory
  • If data in sec storage needed, RAM's unused data transferred to sec storage before og data transferred back
  • Slow: processor wait for swap, sec storage slow access time -> slow processing time