‘First question: Will the 64-bit version of Windows 7 run on only 1 core?

Answer = Yes, but…

…But the single-core CPU has to be 64-bit capable.

That rather limits the field, as there aren’t many single-cored processors that are indeed 64-bit capable.

The ones that I know of are: -

On the AMD side there’s the Athlon 64 single-core; probably the best-known of all the 64-bit single-core processors.

The Athlon 64 is available in Socket 754, Socket 939, Socket 940, Socket AM2, and, surprisingly, even in Socket AM2+.

The problem with most if not all the Socket 754, 939, and 940 Athlon 64s, is that they won’t fit a board that is capable of running hardware compatible with Windows 7. Having said that; I’ve seen a Socket 939 motherboard built to run XP running Vista (Which has the same hardware requirements as Windows 7.) on an Athlon 64, but it ran rather jerkily and badly – and not many of the peripheral ports worked.

That leaves us with Socket AM2 and Socket AM2+. The thing with a socket AM2 motherboard, (Which boards are commonly, in most cases, hardware-compatible for use with Windows 7.) is that a processor-upgrade will allow you to run a dual-core Socket AM2 Athlon 64 X 2 processor, as most if not all socket AM2 boards are compatible with dual-core processor architecture. – Therefore there appears to be very little point in running a single-cored Athlon 64 processor on it. – But if you want to do so then there appears to be no reason why you can’t do just that.

In a similar vein, a socket AM2+ motherboard will definitely run a dual-core processor, and may also normally allow you to run a triple or quad-cored Socket AM2+ Phenom on it; ( As I do.) so once again there appears to be no reason to run a single-cored processor on it. – But, having said that, if you want to do so then there appears to be no reason why you can’t do just that.

Staying with AMD, we now come to the Sempron: The Athlon’s inferior relation. There aren’t many 64-bit Semprons around as far as I’m aware, but nevertheless there are indeed some. Sempron 64s are available in Socket 754, also possibly in Sockets 939 and AM2. – The same applies to these socket designations if they hold a 64-bit Sempron as with the Athlon 64 notes above. 

Moving on to Intel we have our last single-cored 64-bit-capable processor that I know of: That being the P4-600 series of processors: Intel’s eventual answer to the Athlon 64 series from AMD.

These processors, in my opinion, suck big time: They use an architecture based on the Prestcott design, and were Pentium 4 with a few bells and whistles. You’ll be extremely hard-pressed indeed to find a board that holds one of these processors that has hardware that will support Windows 7. – So in short we can forget that series, as well as Intel, for the purpose of this article.

VIA Technologies announced the Isaiah 64-bit processor in 2004; but I’ve never heard of one being used anywhere. – I just thought I’d mention it anyway.

At the end of the day, then, if you have a motherboard with a single-cored AMD Athlon 64 on it, and it’s a Socket AM2 or AM2+ designation, then there is a good chance that you can run Windows 7 on it as-is. – If, that is, you can’t be bothered to upgrade the processor to a dual-core.

There’s probably something I missed; but for the sake of clarity I can’t be arsed to go on about single-cored processors ad-infinitum.

Final summary: It’s just not worth running Windows 7 64-bit on a single-core processor, even though it’s possible to do so in a couple of cases. – Upgrade the processor instead, if your comp is a candidate and is that old. (Up to 7years old at time of writing.)

That’s about it then; not a lot more to be said. In all honesty I would say that if you have a single-cored processor fitted inside your computer it’s probably time to, and also best to, rebuild or buy new – because upgrading is really not worth bothering about on a board that old at this point in time (November 2010) onwards.

Added 12th October 2011: -

I notice that a lot of people have come to this blog, and been directed to this post by Google, searching “Can I run Windows 7 64-bit on a Pentium 4?”.

- So; to save those people time in searching for a definite answer; here it is: -

Disappointingly for those people; the answer is usually NO. in most cases, Pentium 4 is a single-cored 32-bit processor that is not capable of handling a 64-bit-instruction-set. _ BUT in 2004 Intel shipped out updated versions of its Xeon and Pentium 4 processor families supporting the new 64-bit instruction set. – So it might just be possible… My take on it: “Who the fuck would want to use a processor architecture which is that old?!”

‘Hope that helps. In my opinion, whichever type of P4 you’re running; you’d be better off buying a new motherboard, + new RAM, and a new processor rather than run Windows 7 64-bit on a P4… In fact to save yourself loads of hassle at the end of the day, go buy yourself a new computer, and keep running XP on the P4 until it claps out.