CS VM

• Virtual memory

  A type of memory in HDD or SSD that can be used as an extension to the RAM, created for temporary use
• Virtual memory creation


  1. Partitioning part of the hard drive

  2. Used when RAM is full
• RAM is full due to multiple programs running

  Likely to cause a system crash
• Virtual memory


  RAM + swap space on the hard disk or SSD
• Advantages of Virtual memory

  • Programs can be larger than physical memory and still be executed
  • No need to waste memory with data that isn't being used (e.g. During error handling)
  • Reduces the need to buy and install more expensive RAM memory
• Disk thrashing


  Main memory fills, more and more data needs to be swapped in and out of virtual memory leading to a very high rate of hard disk read/write head movements
• Thrash point


  Execution of a process comes to a halt since the system is so busy moving data in and out of memory rather than doing any actual execution
• Ways to reduce disk thrashing

  • Installing more RAM
  • Reducing the number of programs running at a time
  • Reducing the size of swap file
  • Using SSD rather than HDD
• Cloud storage


  A method of data storage where data is stored on remote servers, with data redundancy
• Types of cloud storage

  • Public cloud
  • Private cloud
  • Hybrid cloud
• Public cloud


  • Customer/client and cloud storage provider are different companies
• Private cloud

  • Storage provided by a dedicated environment behind a company firewall, customer/client and cloud storage provider are integrated and operate as a single entity
• Hybrid cloud

  • Combination of public and private cloud, some data resides in the private cloud and less sensitive/less commercial data can be accessed from a public cloud storage provider
• Benefits of using cloud storage

  • Customer/client files can be accessed at any time from any device anywhere in the world provided internet access is available
  • No need for a customer/client to carry an external storage device with them, or even use the same computer to store and retrieve information
  • Remote back-up of data with obvious benefits to alleviate data loss/ disaster recovery
  • If a customer/client has a failure of their hard disk or back-up device, cloud storage will allow recovery of their data
  • The cloud system offers almost unlimited storage capacity
• Drawbacks of using cloud storage

  • If the customer/client has a slow or unstable internet connection, they would have many problems accessing or downloading their data/files
  • Costs can be high if large storage capacity is required; it can also be expensive to pay for high download/upload data transfer limits with the customer/client internet service provider (ISP)
  • The potential failure of the cloud storage company is always possible – this poses a risk of loss of all back-up data
• Data security concerns when using cloud storage

  • What physical security exists regarding the building where the data is housed?
  • How good is the cloud service provider's resistance to natural disasters or power cuts?
  • What safeguards exist regarding personnel who work for the cloud service company; can they use their authorisation codes to access confidential data for monetary purposes?
• Network interface card (NIC)

  A device that allows a device to connect to a network, usually part of the device hardware and contains the Media Access Control (MAC) address
• Wireless network interface cards/controllers (WNICs)

  Same as NICs but use wireless connectivity utilising an antenna to communicate with networks via microwaves, normally plug into the USB port or be part of an internal integrated circuit
• Media access control (MAC) address


  A number which uniquely identifies a device on the internet, made up of 48 bits shown as six groups of hexadecimal digits
• Components of a MAC address

  • OUI (Organizationally Unique Identifier) - the first half which is the identity number of the manufacturer
  • UAA (Universally Administered Address) - the second half which is the serial number of the device
• Types of MAC address

  • Universally Administered MAC Address (UAA) - uniquely assigned to a device by its manufacturer
  • Locally Administered MAC Address (LAA) - an address that changes the MAC address of the adapter
• Reasons for changing MAC address to LAA

  • Certain software used on mainframe systems need all the MAC addresses of devices to fall into a strict format
  • To bypass a MAC address filter on a router or a firewall where only MAC addresses with a certain format are allowed through
  • To get past certain types of network restrictions by emulating unrestricted MAC addresses
• LAA

  An address that changes the MAC address of the adapter
• What is UAA? Media access control (MAC)

  The UAA is by far the most common type of MAC address and this is the one set by the manufacturer at the factory
• It is rare for a user to want to change this MAC address
• Organisation

  May wish to change their MAC address
• Reasons to change MAC address using LAA

  • Certain software used on mainframe systems need all the MAC addresses of devices to fall into a strict format
  • To bypass a MAC address filter on a router or a firewall
  • To get past certain types of network restrictions
• Private network

  A router assigns a private IP address to a device that connects to it
• The private IP address is unique on that network, but might be the same as an IP address on a separate network
• Public IP address

  Supplied by the internet service provider (ISP) and is unique on the internet
• All the devices connected to a router have the same public IP address as the router but each have their own different private IP addresses on that network
• Protocols

  Define the rules that must be agreed by senders and receivers of data communicating through the internet
• IP address

  The network and internet use the transmission control protocol (TCP) for communication, and each device on a network has an IP address
• IP address (how?)

  Consists of a 32 bit code, broken down into four groups of three digits, each group being in the range 0 to 255
• Types of IP addresses

  • Private IP address
  • Public IP Address
• Private IP address (what?)

  The IP address of the device within the Devices LAN (Local Area Network)
• Public IP Address

  The address that belongs to your router
• Dynamic IP addresses

  The device retains the assigned IP address for a limited period, known as a lease
• Static IP addresses

  Each device is assigned a fixed (static) IP address that it retains unless changed
• Differences between Dynamic and Static IP Addresses

  • Greater privacy for dynamic IP addresses
  • Dynamic IP addresses can be an issue for VoIP
  • Static IP addresses allow for faster upload and download speeds
  • Static IP addresses are more expensive to maintain