Thursday, May 26, 2011

ARP Address Resolution Protocol

ARP (Address Resolution Protocol) is a low-level TCP/IP standard that works at the data-link layerand operates at level 2 of the OSI model.

It is defined by RFC 825.

It resolves the logical IP (Internet Protocol) address to the physical MAC (Media Access Control) address.

It broadcasts the request for the MAC address of all hosts across the network through the ethernet cable.

An ARP Table listing all IP and MAC addresses is maintained my most systems.

Tuesday, May 3, 2011

Personal Computer System Components Part 1

Identifying Components of Motherboards
  • Motherboard - the spine of the computer
    • a.k.a. system board or planar board
    • Connects together all the other components of  a PC
  • Two major types of system boards
    • Nonintegrated - all the major assemblies are installed as expansion cards
      • These are difficult to find nowadays.
    • Integrated - most of the components that were previously installed as expansion cards are now integrated into the circuitry of the motherboard.
      • Integrated motherboards are cheaper to produce but expensive to repair as the whole motherboard must be replaced when one component breaks.
System Board Form Factors
  • ATX - Advanced Profile Extended
    • The processor and memory are at right angles to the expansion cards and are in line with the fan, allowing the processor to run cooler.
    • This is the primary motherboard in use today.
  • microATX
    • Uses the same component placement design as ATX motherboards but has a smaller footprint.
    • Has fewer memory modules, headers, expansion slots, integrated components, and chassis bays.
    • Was designed for lower wattage power supplies.
  • LPXe
    • Lack formal standardization and its riser card interfaces varied from vendor to vendor. 
    • Was popular in the 1990s until the advent of the Pentium II processor and the Accelerated Graphics Port (AGP).
    • Was inadequate at cooling and accommodating high pin counts.
  • NLX - New Low-Profile Extended
    • Uses riser cards to place the expansion slots sideways on the motherboard so that the reduced vertical space of the low-profile case is used optimally.
    • Was designed to replace LPX but never became as widely used as LPX was.
  • BTX - Balanced Technology Extended
    • Was designed by Intel.
    • Was met with resistance by customers who foresaw ever rising prices and manufacturers who was increased research and development expenses  and greater potential profit loss.
    • Lined up the components that produced the most heat between air intake vents and the power supply's exhaust fan and used a passive heat sink to cool the CPU and other components.

Thursday, April 21, 2011

APM Advanced Power Management

  • Advance Power Management (APM) was created by Microsoft in conjunction with Intel in 1993.
  • It is a BIOS-level programming interface between the hardware and the operating system (OS).
  • APM uses a layered approach to power management.
  • Power States:
    • Full On
      • This is the normal working operation.
    • APM Enabled
      • APM is available if needed.
      • All devices are working at full power consumption but can be powered down if not in use.
      • The CPU clock may be slowed down or stopped
    • Standby
      • Most devices are in a minimal power state.
      • The system state is saved to RAM.
      •  Recovery is quick (near instantaneous).
    • Suspend
      • Most devices are powered off.
      • The CPU clock is off.
      • The system state is saved to disk.
      • Recovery is slow.
    • Hibernation
      • Hibernation is a "special implementation of the AMP Suspend state."
      • The system state is saved to the non-volatile hard drive.
      • The computer is powered down.
      • The BIOS must start up with POST.
    • Off
      • Computer is powered down and inactive.
      • The system state is not necessarily stored.
      • The system must go through the entire boot process to start up.
  • APM has been replaced by ACPI (Advanced Configuration and Power Interface).