Why I have two /dev/sdx entries with a single disk?

Question

In my laptop (running Linux) I have only one SSD, connected to the SATA3 port.

Why I have two sdx entries in /dev directory?

In particular I see /dev/sda and /dev/sdb, and /dev/sda is the SSD:

# fdisk -l

Disk /dev/sda: 128.0 GB, 128035676160 bytes, 250069680 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Identificativo disco: 0x00034e4b

Dispositivo Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048   125954047    62976000    7  HPFS/NTFS/exFAT
/dev/sda2       125954048   190466047    32256000   83  Linux
/dev/sda3       190466048   222210047    15872000   83  Linux
/dev/sda4       222210048   250068991    13929472    7  HPFS/NTFS/exFAT

$ cat /sys/block/sda/queue/rotational 
0

The surprising thing is the following:

$ cat /sys/block/sdb/queue/rotational 
1

So it looks like that /dev/sdb is considered as a magnetic hard disk drive.

What's the point?

EDIT:

# lshw -C disk
  *-disk                  
       description: SCSI Disk
       product: xD/SD/M.S.
       vendor: Generic-
       physical id: 0.0.0
       bus info: scsi@8:0.0.0
       logical name: /dev/sdb
       version: 1.00
       serial: 3
       capabilities: removable
       configuration: sectorsize=512
     *-medium
          physical id: 0
          logical name: /dev/sdb
  *-disk
       description: ATA Disk
       product: SAMSUNG SSD 830
       physical id: 0.0.0
       bus info: scsi@0:0.0.0
       logical name: /dev/sda
       version: CXM0
       serial: S0Z3NSAC905663
       size: 119GiB (128GB)
       capabilities: partitioned partitioned:dos
       configuration: ansiversion=5 sectorsize=512 signature=00034e4b

Answer 1

With the update (lshw … output) there is the answer now:

product: xD/SD/M.S.

That's your laptop's cardreader. Also, capabilities: removable.

UPDATE: As for the mentioned /sys/block/sdb/queue/rotational value being 1, this parameter actually influences the I/O scheduling algorithm in Linux. Probably, it should have been named something like 'minimize-seek' or similar, because this is what it is intended to do.

I'm not sure why it has been set to 1 for your particular device, I'm not that good in the flash memory architecture and technologies. But I can easily imagine an implementation that works better when accessing adjacent memory units first is quicker than jumping here and there over the medium (roughly equivalent to seeking).

Answer 2

The output of lshw in your updated question appears to provide the information you're looking for; it's your flash card reader. Why it would appear as a magnetic drive is unclear to me - I would say this is a bug or a firmware error to represent itself like this.