magnetism-data addressing

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MAGNETIC DATA STORAGE AND RECORDING
DATA ADDRESSING
BY, A. POOJA SHUKLA M.Tech (NANO)
Ist Yr 1821310006 SRM UNIVERSITY
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DATA ADDRESSING

• A data or information found in a particular
  address
• A data can be randomly selected or easy to find
  in the given array with the help of the given
  address
• Types of data addressing,
• CHS
• ECHS
• LBA

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ADVANTAGES

• Write Protection
• Erasing
• Security
• Removable media
• Removable device
• Managing

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BIOS
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• Basic Input Output System.
• Is a set of initial code to run your PC.
• Intel have designed their CPUs always to begin
  execution of code at address FFFF0.
• The first instruction is a jump instruction to
  the main part of BIOS code which could be
  "anywhere" else
• As well as testing and initializing the hardware
  in the Power On Self Test (POST)

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• For the purpose of booting up the computer, the
  BIOS is used for three main functions
• Providing a set of assembler subroutines that can
  be called by the operating system and whose
  function is to access the hardware components of
  the computer such as hard disk.
• Initiates Power On Self Test (POST).
• Allowing changes to the low level setup options.
• Initiating the boot sequence after a hardware
  Reset.

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ATA
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A set of standards called the ATA
(AT-Attachment) came into being in 1989 that
effectively put a boundary on what was possible
in terms of cylinder, head and sector numbers.
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• ATA-5 says (amongst other things) that
• The cylinder number must be represented by 16
  binary digits.
• The head number must be represented by 4 binary
  digits.
• The sector number must be represented by 8 binary
  digits.
• A total of 28 bits.

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CYLINDER HEAD SECTOR (CHS)
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• CHS, Method for giving addresses to each
  physical block of data on a hard disk drive
• It can be low level formatted to different
  capacities

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• Identifying individual sectors on a disk by
  their position in a track
• The track is determined by the head and cylinder
  number
• For addressing the sector in smallest unit

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Hard Disk Geometry

• Description Terminology
• Heads on a Platter Head
• A stack of Rings or "Tracks" Cylinder
• Segment Sector

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Where the data is physically on the disk?

• disk controller allows us to specify only the
  Cylinder, Head and Sector that we want to access
• The disk controller calculates where the data is
  physically on the disk and hands the data back to
  us
• More accurately CHS is a pointer in memory to the
  data.

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How the physical disk is accessed

• If we wanted to access one particular sector, we
  could reference it by specifying
• C which head it was on,
• H which cylinder it was on and finally
• S which sector it was on.
• That would then uniquely identify the sector that
  we wanted to access.

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CHS Values

• 16-bit Cylinder value (C)
• 4-bit Head Value (H)
• 8-bit Sector Value (S)
• Old BIOS
• 10-bit C
• 8-bit H
• 6-bit S
• Limited to 528MB disk

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LOGICAL BLOCK ADDRESSING (LBA)
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• Used for specifying the location of blocks of
  data stored
• Generally in secondary storage system eg, hard
  disks
• It is an simple linear addressing scheme
• Blocks are arranged by an integer index
• example LBA 0, LBA 1

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• The five most important things to note about LBA
  are
• LBA is a translation method based on the CHS
  addressing scheme
• LBA was not (as many web sites claim) invented to
  overcome any disk size limits
• It is simply a different way of accessing the
  hard disk
• LBA does not require the BIOS to know anything
  about the disk geometry to access the disk
• LBA is used to address data

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EXTENDED CHS (ECHS)
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• It is also called as large mode CHS
• It uses BIOS translation method
• It is inherited by CHS mode to be in given size
  barrier (504 MB)

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• The BIOS coders agreed on a way round the 504 MB
  limitation. They came up with a system called
  Enhanced CHS, or ECHS.
• ECHS is a simple translation method written on
  the end of the interrupt INT13h.
• In summary, this is what happens
• O/S --gt INT13h --gt ECHS Translation --gt CHS call
  --gt Disk Controller

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• Consequently, the requirements for this type of
  disk access are as follows
• An operating system that can make INT13h calls.
• A BIOS that understands INT13h calls.
• A BIOS that can perform the ECHS translations.
• A BIOS that can make CHS calls.
• A disk controller that understands the
  (translated) CHS values referenced.

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Storage Characteristics

• Volatility
• Non-Volatile
• Volatile
• Mutability
• Read/Write
• Read Only
• Slow Write, Fast Read Storage
• Accessibility
• Random Access
• Sequential Access
• Addressability
• Location
• File
• Content

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THANK YOU!!