From V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016) :
SVS
Single Virtual Space (IBM, OS, OS/SVS)
From The Free On-line Dictionary of Computing (30 December 2018) :
OS/VS2
Single Virtual Storage
SVS
An operating system from IBM, released
with the IBM S/370 and originally known as OS/MVT. OS/VS2
R1 was known as SVS (Single Virtual Storage) as it had a
single 16 MB virtual address space. OS/VS2 R2 was known as
MVS - Multiple Virtual Storage.
(1999-01-13)