You can measure the free space and total space of all mounted file systems using the df command.
No. Windows is pretty much the only operating system that cares about primary vs. logical partitions when it comes to booting. Linux will happily live in logical partitions. That being said, with UEFI becoming that standard, logical vs. primary partitions aren't even going to be concepts anymore, as the GPT scheme doesn't limit partition counts the same way as MBR, allowing hundreds of primary partitions, way more than even highly specialized applications would ever need.
It should have the same limitations as any other operating system if you solely work with physical volumes - 4 primary partitions on MBR, unlimited on GPT (though Windows will limit it to 128). Otherwise, if you use something like LVM, it would be unlimited logical partitions, across a single disk or multiple disks.
Same as it is for any other operating system: A primary partition is a "physical" partition that the Legacy BIOS's MBR partition table can recognize. Contrast this with a logical partition, which is a partition stored in an extended partition to work around Legacy BIOS' inability to handle 4 real, physical, primary partitions at a time. Today, on UEFI systems which use GPT, the "primary partition" vs "logical partition" concept is pretty pointless, as you can have as many true-to-life partitions you want on your hard disk due to the face UEFI does things a load better than Legacy BIOS.
man fdisk
You can use a program called GParted to add, edit, and delete partitions.
in Linux this is the second logical drive inthe extended partition on the primary slave hard drive
That depends on what primary partition the fourth extended partition has been placed on. If it was on the first primary partition, it would be /dev/sdb5 (or /dev/hdb5). If it was on the second primary partition, it would be /dev/sdb6 (or /dev/hdb6). If the third, /dev/sdb7, etc... Of course that's assuming you have placed all your logical partitions in a single primary partition. There are several other arrangements you could theoretically have made.
Logical volumes do not have the same restrictions as physical volumes, regardless if it is created in Windows, Linux, MacOS, or any other operating system. The specific details of advantages of a LVM will be documented on their official project site.
Fdisk is a command that can be used in Linux to manage partitions. With this command one can view all disk partitions or delete partitions. For detailed information on step by step instruction for using this command one can access 'The Geek Stuff' website.
Volumes are storage areas, such as partitions and disks.
Not all Linux partitions are ext3. It just happens to be the most popular file system. ext3 was created especially for Linux, so it is free from any patent issues involved with some other file systems.
Primary partition:you can install additional Operating system (eg:- windows 8, linux etc.)Logical Partition:Just additional drive which can be used to store additional data/ normal files/ software.