What is the difference between FS0 and BLK0 in UEFI shell mappings?

Question

I think FS stands for filesystem, but I don't know what BLK stands for. Not only that, but what are the meanings behind the pci hierarchy parameters. i.e. When I see HD(1,MBR,0x0003B) what does "1","MBR", and what looks to be an address, stand for?

Here's the mapping table I'm looking at in UEFI shell:

Mapping table
  FS0: Alias(s):HD21a0e0b:;BLK1:
      PciRoot(0x0)/Pci(0x1D,0x0)/USB(0x0,0x0)/USB(0x4,0x0)/HD(1,MBR,0x0003B)
  FS1: Alias(s):HD23a0a1:;BLK4:
      PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x0,0x0,0x0)/HD(1,MBR,0x00000000,0x3F)
 BLK3: Alias(s):
      PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x0,0x0,0x0)
 BLK0: Alias(s):
      PciRoot(0x0)/Pci(0x1D,0x0)/USB(0x0,0x0)/USB(0x4,0x0)
 BLK2: Alias(s):
      PciRoot(0x0)/Pci(0x1D,0x0)/USB(0x0,0x0)/USB(0x4,0x0)/HD(2,MBR,0x0003B)

I'm guessing BLK's are available ports and FS's are physical things that are plugged into those ports. It looks like once somethign is plugged into a BLK, it becomes an FS, but still retains its BLK value. i.g. FS0=BLK1

what was the uefi shell command you were using, `map` with what flags? — polym, Jun 23 '14 at 19:54
sorry couldn't find more about it. Especially about the hex numbers `0x...` :(. See my last edit! — polym, Jun 23 '14 at 22:24

score 6 · Accepted Answer · edited May 08 '16 at 00:17

According to archwiki:

fsX means filesystem
blkX means block device or data storage device

MBR should mean Master Boot Record

HD should mean Hard Drive

1 might mean Primary, 2 Secondary Partition

That hex number after MBR could be the device signature or disk identifier. Or maybe an offset of that device to important information.

Links that might help further:

What is the difference between FS0 and BLK0 in UEFI shell mappings?

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