[ddwrtuser001]

I am using Linksys E4200 with very new version of dd-wrt.

I have three laptops connected with each other via the wireless by using Windows 7's default network. I am trying to move a 4GB file from one laptop to another, the Windows 7 tells me it will be around 1 hour! Then I go to look at the wireless speed on my laptop, most of time, it says 43.3Mbps. Why the speed is so slow?

My version of dd-wrt is this: DD-WRT v3.0-r33006 mega (08/03/17)

[kernel-panic69]

That version isn't very new. That is two years old. I personally do not have sharing or anything smbd/nmbd-related set up on my LAN - I have thumb drives if I need to grab something from one device to use on another, if I can't just download the file(s) from the Internet. I'm curious if it is your wireless configuration. Auto channel and plain Mixed network mode is not a good idea. Some good starting point articles of interest:

https://www.stevejenkins.com/blog/2013/01/my-cisco-linksys-e4200-dd-wrt-settings-for-max-speed/

https://wiki.dd-wrt.com/wiki/index.php/Basic_Wireless_Settings

https://wiki.dd-wrt.com/wiki/index.php/Advanced_wireless_settings

I am currently running 40854 K3.x on my E4200. If you have any specific questions, ask here or in PM.