Is this correct ?

[#1]

In theory Windows 7 32 bit can use up to 4GB of  RAM but the correct figure is around 3.6 rather than 4.
Windows 7 64 can use the full 4GB of RAM (assuming that's the amount you have).
Is this correct ?
If you wish to upgrade the amount of available RAM from 4GB what is the next logical step, is it 8GB or could you replace a 2GB with a 4GB ?

[#2]

It depends on your present memory configuration and how many memory slots you have on the motherboard
You should have either 2 or 4 slots filled not 1 or 3 for dual channel operation.
If you have 2 x 2GB at present and want to increase the memory then adding 2 more sticks is the way to go and whether you add 2 x 1GB or 2 x 2GB is up to you but given the low price of memory I would add 2 x 2GB
Of course if the motherboard only has 2 slots then it gets expensive and then you need to ask whether you have any programmes which can use the extra memory (are they 64 bit) or whether you have several memory hungry programs running simultaneously

[#3]

http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778%28v=vs.85%29.aspx#physical_memory_l...
Memory upgrades can depend on the motherboard and a read of it's manual can provide the answer.

[#4]

alternatively this will tell you what you can do http://www.crucial.com/store/drammemory.aspx

[#5]

One problem I ran into when upgrading memory was the revision numbers. I had 1.5 gig running vista 32, I bought another 2x 1 gig sticks, exactly the same spec but my computer would not boot, I put the new 2x 1gig sticks in only, and it booted, but the new and old memory would not work together. I sent back the 2x 1gig sticks and they sent me 2 new ones, still the same problem. I googled for an answer and I found out even if the memory is exactly the same spec, if the revision numbers are different then you could have a problem.

[#6]

@jim , crucial memory  scan tells me i can upgrade to a 34Gig set @ $383.99
but am happy with my 8 gig 

[#7]

http://www.crucial.com/uk/

[#8]

here you go Strat 

[#9]

On 32-bit Windows, the number of memory ADDRESSES corresponds to around 4GB. Imagine this as a system-wide pool of addresses. The reason you don't get the full 4GB available for your main system memory is that some of those addresses will be used by other hardware. So that system-wide pool, which is 4GB on 32-bit, must be spread across every hardware device, including your RAM. For example, if you have a 512MB graphics card, it requires that amount of addresses, so 512MB's worth of memory addresses are taken. A few more might be used if you have a separate sound card or a TV tuner. These devices don't actually use any of your RAM per se for storage, it's just that by the time they have had addresses allocated to them, there aren't enough left to allocate all of the system memory. (there are tricks to remap addresses above the 32-bit boundary, but really bad things can happen with some drivers)
On 64-bit Windows, there are several orders of magnitude more addresses, so at the current time the only limit is an artificial one at 192GB, and I can't imagine that there are many desktops/workstations in the world in 2012 which need that amount!

[#10]

There was me thinking it was to do with the base 8 thing in the same way that 32bit systems can only use integer timestamps up to sometime around 2030