Tag: bytes

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Hard Disk Partitions

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Hard Disk Partitions refers to the creation of logical drives for effective memory management and a partition is the logical drive for storing the data. Hidden partition created on a drive can hide the data. The inter-partition gap is the space between the primary partition and the secondary partition. If the inter-partition drive contains the hidden data, use disk editor utilities like Disk Editor to change the information in the partition table. Doing so will remove all the references to the hidden partition, which have been hiding it from the operating system. Another way of hiding the data is to place the digital evidence at the end of the disk by declaring a smaller number of bytes than the actual size of the drive. Disk Editor allows investigator to access these hidden or vacant areas of the disk.

The partitions are of two types:

  • Primary partition: it is the drive that holds the information regarding the operating system, system area, and other information required for booting. In MS-DOS and earlier versions of Microsoft Windows systems, the first partition (C:) must be a “primary partition,”
  • Extended partition: It is the logical drive that holds the information regarding the data and files that are stored in the disk. Various tools are available for examining the disk partitions. A few of the disk editor tools are Disk Edit WinHex, and Hex Workshop. These tools can help users to view the file headers and important information about the file. Both require analyzing the hexadecimal codes that an operating system identifies and uses to maintain the file system.

BIOS Parameter Block (BPB)

The BPB is data structure situated at sector 1 in the volume boot record of a hard disk and explains the physical layout of a disk volume. It describes the volume partition on partitioned devices such as hard disks, whereas on the un-partitioned devices it describes the entire medium. Any partition that includes the floppy disks can use BPB, which would also describe the basic file system architecture. The length of BPB varies across the listed file systems listed (i.e. FAT16, FAT32, and NTFS) due to the volume of the data it contains and also due to the types of fields present.

Master Boot Record (MBR) 

Master Boot Record (MBR) refers to a hard disk’s first sector or sector zero that specifies the location of an operating system for the system to load into the main storage. Also called as, partition sector or master partition table contains a table, which locates partitioned disk data. A program in the record loads the rest of the OS into the RAM.

Information about various files present on the disk, their location, and size is the Master Boot Record file. In practice, MBR almost always refers to the 512-byte boot sector or partition sector of a disk. FDISK/MBR commands help in creating MBR in Windows and DOS operating systems. When a computer starts and boots, the B105 refers this first sector for the boot process instructions and information about how to load the operating system.

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The master boot record consists of the structures as mentioned below:

1. Partition Table

Partition table is a 64-byte data structure storing information about the type of partitions present on the hard disk and their location. This table has a standard layout that does not depend on the operating system. The table is capable of describing only four partitions, which are primary or physical partitions. All other partitions are logical partitions linked to one of the primary partitions.

2. Master Boot Code
A small part of the computer code, which the system loads into the BIOS and executes to initiate the system’s boot process. After execution, the system transfers the controls to the boot program present on the active partition to load the operating system.

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Understanding Bit, Nibble and Byte

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Understanding Bit, Nibble and Byte in this article explained  Bit , Nibble and Byte Data storage format of hard disk with how to calculate it.

Bit

A bit, short for binary digit is the smallest unit of data or basic information unit in computing and digital communications. It can contain only one of the two values represented as 0 or 1. They also represent logical values such as true/false, yes/no, activation states (on/off), algebraic signs (+/-) or any other two-valued attribute.

Byte

A byte, short for binary term is a digital information unit of data that consists of eight bits. The byte is representation of the number of bits a system has used to encode one text character. Therefore, it is the smallest addressable memory unit in many computer architectures. Two hexadecimal digits represent a full byte or octet.

Nibble

A nibble, also known as half-byte or tetrade is a collection of four bits or half of an octet in computing. Common representation of a byte is two nibbles.

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Hard Disk Data Addressing

Hard disk data addressing is the technique of assigning addresses to physical blocks of data on the hard drives. There are two types of hard disk data addressing:

1. CHS (Cylinder-Head-Sector)

This process identifies individual sectors on a hard disk according to their positions in a track, and the head and cylinder numbers determine these tracks. It associates information on the hard drive by specifications such as head (platter side), cylinder (radius), and the sector (angular position).

2. LBA (Logical Block Address)

It addresses data by allotting a sequential number to each sector of the hard disk. The addressing mechanism specifies the location of blocks of data on computer storage devices and secondary storage systems such as hard disk drives, SCSI, and enhanced IDE drives. This method does not expose the physical details of the storage device to the operating system.

Data Densities on a Hard Disk

Hard disks store data using the zoned bit recording method, which is also known as multiple-zone recording. In this technique, tracks form a collection of zones depending on their distance from the center of the disk and the outer tracks have more sectors on them than the inner tracks. This allows the drive to store more bits in each outer track compared to the innermost zone and helps to achieve a higher total data capacity.

1. Track Density

It refers to the space a particular number of tracks require on a disk. The disks with greater track density can store more information as well as offer better performance.

2. Areal Density

It refers to the number of bits per square inch on a platter and it represents the amount of data a hard disk can hold.

3. Bit Density

It is the number of bits a unit length of track can accommodate.

Also Read : Tracks & Advanced Format of Sectors

Disk Capacity Calculation

Calculate

A disk drive that has:
  • 16,384 cylinders
  • 80 heads
  • 63 sectors per track

Assume a sector has 512 bytes. What is the capacity of such a disk?

Answer :  The conversion factors appropriate to this hard disk are

  • 16,384 cylinders / disk
  • 80 heads / cylinder
  • 63 sectors / track
  • 512 bytes / sector

Solution

Total bytes = 1 disk * (16,384 cylinders / disk) * (80 heads / cylinder) (1 track / head) * {63 sectors / track) * (512 bytes / sector) = 42,278,584,320 bytes 1 Kilobyte (KB) = 2^10 bytes = 1,024 bytes

1 Megabyte (MB) = 2^20 bytes = 1,048,576 bytes = 1,024 KB

1 Gigabyte (GB) = 2^90 bytes = 1073,741,824 bytes =1,048,576 KB = 1,024 MB

1 Terabyte (TB) = 2^40 bytes = 1,099,511,627,776 bytes = 1,073,741,824 KB = 1,048,576 MB= 1,024 GB

Using these definitions, express the result in GB as:

42,278,584,320 bytes / {1,073,741,824 bytes / GB) = 39.375 GB

Hard disk in a typical computer system has a storage capacity. Data is stored on the hard disk in the form of files.

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Tracks & Advanced Format of Sectors

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Tracks & Advanced Format of Sectors In this article explain hard disk track and diffrent andvance format of sector and there uses.

Tracks

Platters have two surfaces, and each surface divides into concentric circles called tracks. They store all the information on a hard disk. Tracks on the platter partition hold large chunks of data. A modern hard disk contains tens of thousands of tracks on each platter. The rolling heads read and write from the inner to outermost part of the disk. This kind of data arrangement enables easy access to any part of the disk; therefore, hard disks get the moniker as random access storage devices.

Each track contains a number of smaller units called sectors. Every platter has the same track density. The track density refers to the compactness of the track circles so that it can hold maximum number of bits within each unit area on the surface of the platter. It also determines the storage capacity of data on the hard disk. It is a component of area density in terms of capacity and performance.

Sector

Tracks contain smaller divisions called sectors, and these sectors are the smallest physical storage units located on a hard disk platter. “Sector” is a mathematical term denoting the “pie-shaped” or angular part of the circle, surrounded by the perimeter of the circle between two radii. Each sector normally stores 512 bytes of data, with additional bytes utilized for internal drive control and for error correction and detection. This added information helps to control the drive, store the data, and perform error detection and correction. A group of sectors combines in a concentric circle to form a track. The group of tracks combines to form a surface of the disk platter. The contents of a sector are as follows:

  • ID information: It contains the sector number and location that identify sectors on the disk. It also contains status information of the sectors
  • Synchronization fields: The drive controller drives the read process using these fields
  • Data: it is the information stored on the sector
  • ECC: This code ensures integrity of the data
  • Gaps: Spaces used to provide time for the controller to continue the read process

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These elements constitute sector overhead. It is an important determinant in calculating time taken for accessing. As the hard disk uses bits for disk or data management, overhead size must be very less for higher efficiency. The file on a disk stores the data in a contiguous series for optimal space usage, while the system allocates sectors for the file according to the size of the file. If file size is 600 bytes, then it allocates two sectors, each of 512 bytes. The track number and the sector number refer to the address of any data on the hard disk.

Advanced Format: Sectors

New hard drives use 4096 byte (4 KB or 4 K) advanced format sectors. This format uses the storage surface media of a disk efficiently by merging eight 512-byte sectors into one single sector (4096 bytes). The structure of a 4K sector maintains the design elements of the 512-byte sector with representation of the beginning and the error correction coding (ECC) area with the identification and synchronization characters, respectively. The 4K sector technology removes redundant header areas, lying between the sectors.

Clusters

Clusters are the smallest accessible storage units on the hard disk. The file systems divide the volume of data stored on the disk into discreet chunks of data for greater performance and efficient disk usage. Clusters form by combining sectors in order to ease the process of handling files. Also called allocation units, the dusters are sets of tracks and sectors ranging from 2 to 32, or more, depending on the formatting scheme. The file allocation systems must be flexible in order to allocate the required sectors to files. It can be the size of one sector per cluster. Any read or write will consume the minimum space of one cluster.

To store a file, the file system should assign the required number of clusters to them. The cluster size totally depends on the disk volume. For disk volumes, each cluster varies in size from four to 64 sectors. In some cases, a cluster size may be of 128 sectors. The sectors located in a cluster are continuous. Therefore, every cluster is a continuous chunk of space on the hard disk. In a cluster, when the file system stores a file relatively smaller than size of the cluster, extra space gets wasted and called as slack space.

Cluster Size:

Cluster sizing has a significant impact on the performance of an operating system and disk utilization. Disk partitioning determines the size of a cluster and larger volumes use larger cluster sizes. The system can change the cluster size of an existing partition to enhance performance. If the cluster size is 8192 bytes, to store a file of 5000 bytes, the file system allocates whole duster to the file and allocates two clusters of 16,384 bytes if the file size is 10,000 bytes. This is why cluster size plays a vital role in maximizing the efficient use of the disk.

By using a large cluster size, the fragmentation problem diminishes, but it will greatly increase the chances of unused space. The file system, running on the computer, maintains the cluster entries.

Clusters form chains on the disk using continuous numbers for which it is not required to store the entire file in one continuous block on the disk. The file system can store it in pieces located anywhere on the disk as well as moue it anywhere after creating the file. This cluster chaining is invisible to the operating system.

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