SV stands for 'Swiched VMware'

See below for in-depth explanation:

http://www.cisco.com/c/en/us/about/security-center/ios-nx-os-reference-guide.html#11

Cisco NX-OS Software Numbering

Cisco NX-OS Software is a data-center-class operating system that provides high availability with a modular design. Cisco NX-OS Software is based on the Cisco MDS 9000 SAN-OS Software and it supports the Cisco Nexus Series and the Cisco MDS 9000 Series Multilayer Switch. The Cisco NX-OS Software contains a kick start image and a system image, both images contain a major release identifier, a minor release identifier, and a maintenance release identifier, and they can also contain a rebuild identifier, which may also be referred to as a Support Patch. (See Figure 6.)

Cisco NX-OS Software for Nexus 7000 Series Switches and MDS 9000 Series Switches uses the numbering scheme that is shown in Figure 6.

Figure 6. Cisco IOS NX-OS Numbering for the Cisco Nexus 7000 and MDS 9000 Series Switches

For other members of the family, Cisco NX-OS Software uses a combination of platform-independent and platform-dependent schemes as shown in Figure 6a.

Figure 6a. Cisco IOS NX-OS Software Numbering for the Nexus 4000 and 5000 Series Switches and Nexus 1000 Virtual Switches

The platform designator is N for the Nexus 5000 Series Switches, E for the Nexus 4000 Series Switches, and S for the Nexus 1000 Series Switches. In addition, the Nexus 1000 virtual switch uses a two-letter platform designation where the second letter indicates the hypervisor vendor that the virtual switch is compatible with, for example V for VMware. Applicable features, functions, and fixes in the platform independent code are present in the platform dependent release, in Figure 6a above, applicable fixes in Cisco NX-OS Software Release 4.0(1a) are present in the 4.0(1a)N1(1a) release.