Sep 20, 2010

Few Basics in Nutshell

  • 1 sector = 512 byte
  • 1 partition table = 64 byte
  • Every operating system has kernel and shell. User can work on shell and shell requires kernel to work. Io.sys and Msdos.sys are the kernel files and Command.com is the shell file.
  • Booting sequence of DOS
    • BIOS: Basic Input Output System
    • POST: Power On Self Test.
    • Io.sys: Intialize the I/O devices of the system.
    • Msdos.sys: It sets the DOS environment and checks whether config.sys is present or not. If not, it directly goes to command.com.
    • Config.sys: It loads the drives which are interface between hardware and OS.
    • Command.com: It gives C:\> (current prompt).
    • C:\> 
    • Autoexec.bat: It automatically executes the entries in it just after booting (similar as Startup in Windows).
    • User
  • Commands which present in Command.com files are called Internal Commands and commands which present in the disk drives are called the External Commands.
  • Prompt command
    • Prompt $Q: =
    • Prompt $$: $
    • Prompt $T: Current time
    • Prompt $D: Current date
    • Prompt $P: Current drive and path
    • Prompt $V: MSDOS version
    • Prompt $N: Current drive
    • Prompt $G: >
    • Prompt $L: <
    • Prompt $B: |
    • Prompt $H: \
  • The frequesncy of microprocessor (called internal frequency) is very high (typically in GHz) but the frequency of other devices (called external frequency) is low (typically in MHz). For the smooth communication, microprocessor adjusts internal frequency lower as per the external freqency. The external frequency is called FSB (front side bus). 
  • A small memory present in microprocessr to keep the frequently used commands is called the Cache Memory. Since all frequently commands are taken from the cache memory, hence it enhance the speed and performance of the machine.
  • Memory
    • ROM (Read Only Memory) (Permanent)
      • PROM (Programmable ROM)
      • EPROM (Erasable PROM), can be erased by UV rays.
      • EEPROM (Electrically erasable PROM)
      • Flash ROM
    • RAM (Random Access Memory) (Temporary/Volatile)
    • SRAM (Static RAM): Faster, made by flip flops, costly, no need of refreshing.
    • DRAM (Dynamic RAM): Slower, made of transistors, need refreshing circuit, cheeper.
      • Asynchronous: Internal and external memory are not same. Type: FPM (Fast Page Memory)/also called the magic memory, EDO (Extended Data Out), BEDO (Bus EDO) are asynchronous RAM.
      • Synchrounous: Internal and external memory is same. SDRAM (Synchronous DRAM), RDRAM (Rambhous DRAM), DDRRAM (Dual Data Rate RAM), DCDDRAM (Dual Channel DDRRAM) are synchronous RAM.
  • Static RAM is faster than the dynamic RAM (hence the static RAM is costlier than the dynamic RAM). Internal memory is made of static RAM and external memory (RAM) is made of dynamic RAM.
  • Memory Slots
    • SIMM (Single Inline Memory Module): White, metal locks, 30/72 pins, 4-8 slots, used for SDRAM.
    • DIMM (Dual Inline Memory Module): Black, plastic locks, 168 pins, used for SDRAM/RDRAM.
    • RIMM: (Rambhous Inline Memory Module): Black, palstic locks, 184 pins, come with heat sink, used for SDRAM.
    • DDRDIMM (Dual Data Rate DIMM): Black, plastic locks, 184 pins, used for DDR RAM.
  • Chipset: Set of controllers is called chipset. The second biggest IC (except microprocessor) on the motherboard is the chipset. Chipset decides which kind of processor/memory can fix on the motherboard and because of this, motherboard is called the chipset motherboard.
  • Expension Slots
    • ISA (Industry slandered Architecture): Black, big, one cut, 8/16 bit.
    • EISA (Extended ISA): Black, 2 cuts, 32 bit, ISA card can be fix in EISA slots but speed will not change.
    • VESA (Video Electronic Slandered Association): Brown, smaller, 32 bit.
    • PCI (Peripheral Component Interface): White, smaller, 32/64 bit, 1 cut in 32 bit and 2 cuts in 64 bit.
    • AGP (Accelerated Graphical Port): Only for video/display card, brown, one cut, 32 bit.
    • AMR (Audio Modem Raiser): Brown, smaller than PCI, 1 cut, specially for audio card.
    • CNR (Communication Network Raiser): Very small, for network card.
  • Elements of FDD
    • Read/write head.
    • Stepper motor.
    • Spindle motor.
    • Electronic control circuit.
    • Sensors
      • Track 0 sensor.
      • Write protect sensor.
      • Disk change sensor.
      • Density sensor.
      • Index sensor.