In an interesting crossover between current events and Retrocomputing, the vulnerability known as "Meltdown" was publicly disclosed on January 3rd 2018. The retro-computing tie-in is that this vulnerability is reported to impact all Intel microprocessors back to the 1995 release of the Pentium Pro (P6 micro-architecture).
In the late 1990s, the dominant OS's for Intel machines were MS-DOS, which was slowly being retired, and Windows 95 and 98, which were the replacements still underpinned by MS-DOS. Of course, Windows NT was also on the rise, but was most prevalent in enterprises. My question is which of these OS's were TECHNICALLY vulnerable to Meltdown, taking into account whether the OS offered any real attempt at memory protection?
My impression is that MS-DOS and Windows offered no such protection*. Therefore, it's arguable that they weren't actually vulnerable to Meltdown, by virtue of the fact that no such vulnerability needed to exist to allow a rogue process to access "private" data owned by other processes. If this is true, then what time-frame can we pinpoint when systems became vulnerable to Meltdown accounting for OS features that guaranteed memory protection?
*NOTE: I'm recalling dev tools for Windows, like Dr. Watson and Bounds Checker, that seemed to allow full access to process memory without any special privilege.