partitioning - Problem with partitions after reinstallment

I originally had Windows10 installed on my laptop.

I did partitioning, installed Ubuntu 14.04, had a low-graphics mode problem but couldn't solve it and then tried to reinstall Ubuntu.

In this process, I think I have erased the Windows10 and have instead installed Ubuntu, again.

When I log in to Ubuntu, I see two disks, each with /boot folder in it.
And the below is the information of my partitioning:

Disk /dev/sda: 2000.4 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x000e299b

Device Boot      Start         End      Blocks   Id  System

/dev/sda1   *        2046  3906437119  1953217537    5  Extended
Partition 1 does not start on physical sector boundary.
/dev/sda5            2048     7999487     3998720   82  Linux swap / Solaris
/dev/sda6         8001536   398620671   195309568   83  Linux
/dev/sda7       398626816  3906437119  1753905152   83  Linux

Disk /dev/sdb: 256.1 GB, 256060514304 bytes
255 heads, 63 sectors/track, 31130 cylinders, total 500118192 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
Disk identifier: 0x0f838f59

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *        2048   498127989   249062971    7  HPFS/NTFS/exFAT
/dev/sdb2       498128896   500115455      993280   27  Hidden NTFS WinRE

Is my understanding of partitioning correct? That is, is the Windows deleted?

If so, is there a way for me to fix the problem having two partitioned Linux system and make it into one?

Any answer would be helpful. Thanks.