Hi!
I am new here ! Interesting site and very helpful! 
I have a Japanese OS TX51B and want to upgrade the memory.
I can see in the VAIO info for my VAIO that says the memory module is VGP-MM1GA and runs at 400mHz.
The replacement I see on the web shows the speed to be 667 mHz. I have been told differently about what I should do!
1. Buy and install the 667mHz module because your VAIO will just default to the lower speed,
2. you must buy the correct speed module, i.e 400mHz!
Now this may be a Cardinal Sin, but I was also told I can buy another companies module, and I will be in Japan in 3 weeks time. I know Buffalo do a module for 7800 Yen, so about 35 pounds. But of course, Sony say only use genuine Sony modules !
Is buying Sony memory really critical ? Buffalo seems repuatble in Japan.
My last thought is that I want to buy the long life battery VGP-BPL5 and I think I just switch batteries, then charge the new battery up, and that's it! But I was told that I will need to change something in the BIOS !
Any advice welcomed!
Ofiaich :smileygrin:
1st off welcome to CV.
Sony memory is actually usual Hitachi so any brand is not a problem.
As for the speeds you are correct about it defaulting to the speed it can deal with so to be honest i would buy the slower 400MHz and save the money because thats all it'll run at.
Crucial is the best place to get the RAM from as they sell you what you actually need.
Hope that helps 
Your welcome
Say hello to Japan from me! 
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