Why mbr is 512

LBA Logical block addressing is much recent scheme used to locate blocks of data. You can calculate bytes from LBA by multiplying it with sectors. This partition scheme clearly show limitation of only availability of 4 partition. That's the reason we have something called as extended partition scheme. Recent OS also introduce GPT partition scheme which overcome this limitation of storing partition entry on MBR and making possible to have large numbers of partition possible.

Published 22 November 4 min read. By Shubham Dubey. Where is my MBR? You can view the same data in Windows using HXD hex editor. Below is the screenshot of that. Lets try to understand what information this bytes of data contain.

Lets break down these 16 bytes entry of a partition into meaningful data. All data in partition entries is in little endian format. Disk Signature Located at byte , this is simply a unique identifier for the disk. This is typically used by Windows to remember the assigned drive letters for each partition, but is also used by various operating systems to identify the correct boot volume.

An invalid magic number indicates a corrupt or missing MBR, therefore these bytes are critical to booting or using the disk. Also, please keep in mind that the Magic Number is a hexadecimal number and is often represented as 0xAA55 or AA55h, but when viewed in a hex or disk editor it would be displayed as: "55 AA" When any part of the MBR is missing or corrupt, the machine will not be able to boot.

These fields are essential for starting the computer. The master boot code uses these fields to find and load the boot sector of the active partition. The Starting CHS fields for non-active partitions point to the boot sectors of the remaining primary partitions and the EBR of the first logical drive in the extended partition.

Knowing the starting sector of an extended partition is very important for low-level disk troubleshooting. If your disk fails, you need to work with the partition starting point among other factors to retrieve stored data. The Ending Cylinder field in the partition table is 10 bits long, which limits the number of cylinders that can be described in the partition table to a range of 0—1, The Starting Head and Ending Head fields are each one byte long, which limits the field range to 0— The Starting Sector and Ending Sector fields are each six bits long, which limits the range of these fields to 0— However, the enumeration of sectors starts at 1 not 0, as for other fields , so the maximum number of sectors per track is Email Required, but never shown.

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