when was this 10 version first released to the public?
July 29, 2015
Public release
On July 29, 2015, Microsoft officially announced that Windows 10 would be released for retail purchase as a free upgrade from earlier versions of Windows. 
system requirements for windows 10 pro 32 bit 7 GB of disk space, The 64-bit variants require a CPU, USB flash drive etc who is the developer of this operating system? Microsoft
On July 29, 2015. 29 July, 2015. July 29, 2015.
Windows 10 Windows 10 Windows 10
Introduction Release Release
Windows 10 is a series of operating systems developed by Microsoft and released as part of its Windows NT family of operating systems. It is the successor to Windows 8.1, released nearly two years earlier, and was released to manufacturing on July 15, 2015, and broadly released for the general public on July 29, 2015.  The campaign culminated with launch events in thirteen cities on July 29, 2015, which celebrated "the unprecedented role our biggest fans played in the development of Windows 10". On June 1, 2015, Microsoft announced that Windows 10 would be released on July 29, that year.
wiki:4873627
Windows 10 [SEP] Public release
On July 29, 2015, Microsoft officially announced that Windows 10 would be released for retail purchase as a free upgrade from earlier versions of Windows. In comparison to previous Windows releases, which had a longer turnover between the release to manufacturing (RTM) and general release to allow for testing by vendors (and in some cases, the development of "upgrade kits" to prepare systems for installation of the new version), an HP executive explained that because it knew Microsoft targeted the operating system for a 2015 release, the company was able to optimize its then-current and upcoming products for Windows 10 in advance of its release, negating the need for such a milestone.