Thanks , will find out more and reply again.
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1. There's no need to worry about this, as you can easily mitigate this by using a UPS if you are afraid of sudden power cuts during a BIOS flash

2. Zen 4 CPUs will no longer use the AM4 socket, instead it will use a new, tentatively named AM5 socket, along with DDR5 memory

3. For most users (I myself encodes videos as well), a 3600 should do the trick, but if you want faster performance, there's always NVENC or GPU encoding which can be faster than software/CPU based encoding

4. I don't recommend single channel memory as this will hold back the CPU performance quite a bit; always go for a 2x16GB stick if you want 32GB. Avoid doing the 1x16GB then add another 16GB sticker later method as the current RAM you bought may no longer available in the market, or has been replaced with a different model, or has different specifications

5. I don't watch 8K videos so I cannot speak for this

6. Yes, and you can get an AM4 bracket for the Hyper 212 EVO by messaging Cooler Master Malaysia Facebook page

On idle, I'm averaging 50-ish degrees, but I'm not sure about the load temps as I don't monitor them

7. No, starting from first gen Ryzen - Windows 10 is the only supported version on Windows (unless you are talking about Linux as well). There's really no point of going back to an unsupported and unpatched system unless you want security vulnerabilities

Even if you can install 7, there are things like drivers will not work on it (I myself actually used 7 on my current build at some point as I needed to backup my data before migrating to 10, only to find out a lot of features like USB ports simply won't work on 7)

1. So buying any BIOS without a recovery button is still fine.It not able UPS , sometimes , bios will get corrupted if pc is infected with virus on UEFI.So it's the best to have a 2nd BIOS .I will check for which budget motherboard that have it.
2. If in the case , getting a cheaper motherboard socket like B450 is much cost much less than B550.It'll be around 2021 0r 2022 for AM5 , not sure maybe 10 cores? any news leak about it ?
3. When converting , whether a NVENC gen 6 still costly for turing card 2k series.SO any example video bunny encoding ? you are using 3600 , can tell on how is the performance when converting some video maybe 1080p mp4 vp9 to 1080p hevc 265 without lossing quality or maybe 1-5% is acceptable. Soon av1 in future.
4. What does different model ? using same brand but maybe in future will upgrade to the same model but surely will have a different dies but since i didn't OC do you think is better to get both at the same time ? but i do not need much too much ram 16GB is enough currently.
5. I too do not watch but just wanted to confirm whether 3600 can run 8k youtube build in graphic chipset am4.
6. Maybe find Hyper 212 EVO but what is the fan speed rpm and noise level ? actually what fan Hyper 212 EVO is using if it's silent ?
7. Windows 7 enterprise still support until 2023 if I remember , and there are custom patch for security release.So software only works with windows 7 and windows 10 sometimes is too troublesome with everytime updates takes time , no offline updates for user who only use slow internet smyx speed.
Not sure about USB port , are all usb 3 support backwards to 2.0 ? If not , try to find a motherboard which support USB 2.0 or a pci 2.0 card for usb 2.0 or ps/2 port motherboard or even slimslip 3.0 driver into windows 7 but need to dig which driver compatible.
Thanks I get most of the answer , now just need to research for 3600 vs 3700x speed on converting , suitable motherboard and ram.Hope price will drop at 9.9 or 11.11 promotion + voucher.
and convert it to something other format or quality , how long it would take ?