Beldar wrote: ↑Sat Oct 10, 2020 9:26 am
so I'll look to buy a pair of Dual-Channel DDR3 4GB strips
Actually the RAM sticks are not dual-channel by themselves

RAM works dual-channel when you put a pair of RAM sticks into your Thinkpad, like you have now
I understand dual-channel means that data exchange can happen with both ram sticks simultaneously
dual-channel is faster than single channel and the general opinion was that having two ram sticks match as closely as possible helps ensure the RAM indeed ends up working in dual-channel mode
Beldar wrote: ↑Sat Oct 10, 2020 9:26 am
same brand
Not just same brand, just buy two together. So long as you're buying from a sane seller that should ensure you will get identical ram sticks
Beldar wrote: ↑Sat Oct 10, 2020 9:26 am
The other info you've given is unfortunately over my head
Hmm.. was there much other info?..

I'd suggest to stick to reputable brands, look among reputable sellers, look for low price and once you find somehow confirm it's indeed 2Rx8.. If you know exact manufacturer's designation for your RAM you can look up details somewhere online and thus see if it's 1Rx8 or 2Rx8. Many thanks to Screamer for correcting me.. I enjoy learning little stuff like this.
What screamer was saying is that it's not important if your memory is marked as DDR3 or DDR3L, he said that so long as it's a reputable brand it should work in either case.
He also said that of all
varieties of DDR3 you may wish to avoid PC3-6400 aka DDR3-800 since it's a little on the slower side but all other kinds PC3-8500 aka DDR3-1066, PC3-10600 aka DDR3-1333, PC3-12800 aka DDR3-1600, PC3-14900 aka DDR3-1866, ... are equally suitable. In fact they will all run at PC3-8500 aka DDR3-1066 speed since that is the maximum T510 supports. In fact you have seen your current RAM running at 532Mhz which corresponds to PC3-8500 aka DDR3-1066 row in that wikipedia page. Lower spec modules may be a little cheaper than higher spec ones, so PC3-10600 aka DDR3-1333 may be cheaper than C3-14900 aka DDR3-1866 and since they will work just the same way you're well advised not to look for higher specs.
Make sure to purchase
SO-DIMM modules not the cheaper
DIMM ones

! You probably know DIMM-s are for desktops, they are longer, have a look at the photos. In fact DDR3 SO-DIMM-s differ say from DDR2 or DDR4 SO-DIMM-s in the location of that notch along the "bottom" side. Make sure you're able to recognise DDR3 SO-DIMM from other types of memory just but their looks (like
here). This will help you find your way around Asian sale sites with 1600 items advertised on them

While looking at TaoBao I even saw some offers that combined DDR2 and DDR3 under the same sale and you had to choose the right type from a multiple-selection. Also make sure not to buy accidentally 2*2Gb, e.g. what you have now. While looking through TaoBao or ebay especially for lower price offers it's easy to get confused about what you're buying. In fact I had to have superbuy.com, my TaoBoa intermediary return a pair of RAM sticks because I accidentally had them buy 2*2Gb for me and only recognised my mistake when I saw detailed photos..
What are good brands? I'd think genuine Crucial is a good one, my T520 came from factory with Samnsung memory, I've purchased Kingston Hyper-X for my Thinkpads and feel happy about it, but that's an overkill for T510 being DDR-1866.. BTW among 7 8Gb Hyper-X DDR3 SO-DIMM modules I got one proved to be faulty, ebay seller refunded me for it.. So sh-t does happen occasionally.. Which may be an argument in favour of ebay or other places where refunds are easier..