I want to know what are the deciding factors for choosing between a 64Mb switch and a 128Mb switch
I do not believe you are talking about DRAM size but flash.
Doesn't make any difference whether or not your switch has 64mb or 128mb flash. At the end of the day, a switch can store a minimum of two full IOS and, in some cases, three full IOS. So if you know how to play with the IOS, then this matters. If you don't then it doesn't matter.
Is there any documnet supporting this
Nope. They are purely based on real-life experience.
how to determine which switch will cater which architecture
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Usually, somewhere on the datasheet amount of RAM supported should be listed.
If you have a choice, or the switch can be RAM upgraded, whether you need added RAM would depend on your network and what feature you intend to use. What would be the thing to watch for would be feature that consume large amounts of RAM. For example, say for some reason you wanted a huge on-board (RAM) syslog. Or, you wanted non-summarized Netflow with extended timers and you have many flows. Or, you're going to have multiple full Internet BGP peers. (BTW, some of the prior examples would not be suitable on many L3 switches.)
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...