Logical Disk vs Physical Disk

Help on how to use HxD.
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EmbSysDev
Posts: 2
Joined: 07 Oct 2022 18:38

Logical Disk vs Physical Disk

Post by EmbSysDev »

Hi all,
Just a query about HxD usage :
I have a freshly formatted SDCARD card.I open with HxD Logical Disk or Physical Disk.

In sector 0 when I open with Logical Disk it shows :
ëXMSDOS5.0�@V����ø��?�ÿ�� ���¬ÚÕ�����������������������€�)±ØìNO NAME FAT32 3ɎѼô{ŽÁŽÙ½�|ˆV@ˆNŠV@´A»ªUÍrûUªu
öÁtþFë-ŠV@´Ís¹ÿÿŠñf¶Æ@f¶Ñ€â?÷â†ÍÀíAf·Éf÷áf‰Føƒ~�u9ƒ~*�w3f‹FfƒÀ»�€¹�è,�騡ø}€Ä|‹ð¬„Àt<ÿt ´»�Íëî¡ú}ëä¡}€ëߘÍÍf`€~�„ �fj�fPSfh��´BŠV@‹ôÍfXfXfXfXë3f;Førùë*f3Òf·Nf÷ñþŠÊf‹ÐfÁê÷v†ÖŠV@ŠèÀä
̸Ífa‚tÿÃ�f@Iu”ÃBOOTMGR ����������������������������������������������������
Disk errorÿ
Press any key to restart
�����������������������������������¬¹��Uª
When I open with Physical Disk :
��������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������œ���‚�þÿÿ� ���¬Ú������������������������������������������������U
Can someone advise why the contents are different in both cases ? The last 2 bytes are the same in both cases viz. 0x55 0xAA.
Cheers !!
Maël
Site Admin
Posts: 1418
Joined: 12 Mar 2005 14:15

Re: Logical Disk vs Physical Disk

Post by Maël »

A physical disk is subdivided into several partitions, a logical disk is usually contained in one partition (there is also a case where a volume/logical disk can span several partitions, but that's rarely the case).

The first logical disk usually starts several sectors inside the physical disk. Look up MBR, GPT and partitioning in general for details, or simply search for the start of the logical disk "ëXMSDOS5.0" in the physical disk to find the start position of the logical disk.
EmbSysDev
Posts: 2
Joined: 07 Oct 2022 18:38

Re: Logical Disk vs Physical Disk

Post by EmbSysDev »

Thank you for replying !
From what I understand, sector 0 in a logical disk is at a different location than the physical sector 0 (which is the first sector of the hard drive).Hope i got that right.
I will read the links you provided,thanks.
Maël
Site Admin
Posts: 1418
Joined: 12 Mar 2005 14:15

Re: Logical Disk vs Physical Disk

Post by Maël »

Maybe these pictures give a rough idea of the concept (LBA, means linear block address and is another word for sector number, so for example LBA 0 = sector 0).
Note that the given sector positions for GPT are not necessarily the same for MBR nor are they fixed. The illustrations have example values.
Also note that while the partition table calls some drives primary partitions and others logical drives/partitions, this is an unfortunate mix of terminology. Under Windows volume or logical drive means any drive that is assigned a drive letter (or could have one assigned to it).
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