Milkth3cow :
I didn't know Pentiums had this feature - but it's called hyperthreading. This is when your CPU interacts with your operating system to make it seem as if it has double the amount of physical cores it has, this boosts your performance in pretty much any CPU-intensive task
i7s are notable to have this feature, which is why they're so commonly used in video editing PC builds seeing as video rendering is heavy on your CPU - and also your RAM.
So yes, you could say virtually you have 2 cores - but physically you have 1.
Someone Somewhere :
Some older Pentiums had it, but it was dropped off the spec sheet when Core turned up.
Intel added it back in when Nehalem arrived.
I think 2nd gen pentium 4s all had it. Intel actually had a short run ad campaign claiming they were the worlds first "dual core" processors. Which of course became a giant joke on the net as AMD released the dual core Athlons almost at the same time... and of course the single core athlons destroyed those fake "dual core" p4s... and the dual core athlons further opened the performance gap. At that point in time it looked like intel was dead as a doornob; with AMD crushing them in single cored performance (a 2ghz Athlon would kill a 3.2ghz p4); had the first great dual cored cpus AND were the first chip maker with a functional x64 bit architecture (m$ actually forced intel to licence the x64 instruction set from AMD, since AMD's worked and intel's didn't). In desperation Intel actually released a netburst based P4-D, which was literally two cpu cores soldered together in what was possibly the worst dual core cpu ever released.
Yeah... for a time there it looked like intel was dead... of course for
some reason AMD's market share never increased, and it turned out it was because intel was bribing hardware manufacturers to not use AMD cpus... (they lost a number of anti-trust suits around the world about their practices during this time... the only reason they didn't lose a big one in the USA was because US anti-trust laws are strange, and basically intel stalled the case in court long enough to regain a technological advantage... which oddly made AMD's case vanish... as US antitrust laws require you to have a superior product being held down... once AMD lost the tech edge, they lost the heart of their case)
Of course meanwhile intel's mobile division, getting creamed by AMD's turon procesors, resurrected a 10 year old scrapped chip design dubbed the P6; and the Pentium M was born. Which of course became the heart of the coresingle and coreduos (with the coreduo intel dropped Hyperthreading, as hyperthreading was almost a dirty word with the beating they took thanks to their marketing and the poor performance from early hyperthreaded cpus), then the core2duos and core2quads... and eventually the core i series... had that quirk of fate in reexamining that old P6 never happened, had the k10 performed close to expectations... had intel not got away with it's monopolistic practices, had AMD not bet the farm and overextended itself opening foundries everywhere while expecting their cpu division to take off... we could be looking at a much more competitive CPU landscape today. And maybe... just maybe we'd be seeing more then 10% improvement in performance every 18months.