This category is for web sites that involve or cover the IBM mainframe computer operating systems: DOS, DOS/VSE, VSE, VSE/SP, VSE/ESA and now z/VSE.
z/VSE is one of IBM's mainframe operating systems. It originated as DOS/360 on the low-end System/360 computers of the mid-1960s.
Sites that also discuss other operating systems are found in Computers/Software/Operating Systems/Mainframe/IBM. Sites that also discuss hardware are found in a subcategory of Computers/Hardware/Systems/IBM.