It completely depends on what apps you have running, as performance is directly impacted by workload. Generally speaking, you may wish you had more RAM than 4GB.
Generally, pretty bad.
This is the correct answer. 4gb could not be an issue at all when running Win7 in VM or they could be a massive issue. This completely depends on the apps you are running. Also the 1.4ghz cpu could be an issue and obviously the standard hdd should be exchanged for an ssd in every case.
This is good advice. If your plan is to always run VMs, the mid range mini with a fusion drive inside would be a much preferable option.Generally, pretty bad.
You should aim for at least a mid-range Mac Mini with 8GB of RAM and a 1TB Fusion Drive.
At the very least, get a Fusion Drive.
Your biggest bottleneck will be the RAM. Yosemite will be happiest with 4GB of RAM which means 0 RAM for the VM. You need 8GB.
Forgot to add one more thing.This is good advice. If your plan is to always run VMs, the mid range mini with a fusion drive inside would be a much preferable option.
Keep in mind that OP is thinking of a Mini with a HDD.Since you don't give the usage, I'll give you some real-world scenarios.
My hardware is a base 2014 MacBook Air, so the hardware is nearly identical to the base Mac Mini, excepting that your screen may use more or less resources, and it uses an SSD. 4GB RAM, 1.4GHz i5, 128GB SSD. (You could easily fit a 120GB SATA SSD to the base model for under $100 and get pretty much the same performance.)
I run several industrial control, diagnostics and repair documentation software that utilize large databases (40GB), talk through serial ports (USB->serial adapters), and over the network. I generally use VirtualBox and Parallels for these. VirtualBox for VMs that I copy back and forth between varying hardware platforms, and Parallels for ones that live permanently on this MBA. I generally allocate 2GB RAM and 2 CPUs to the Windows VMs, and also give the VM better performance settings where applicable. These VMs were copied from PC laptops that generally had Core 2 Duo or 1st gen Core i processors. These systems are legacy that seem like they were ported from older mainframe apps, although they have been continually updated every quarter to use newer technology.
When running just a single VM, performance is great. It easily exceeds the performance of the original machines, and allowed me to consolidate several machines into one MBA, and gain more screen area and MUCH longer battery life.
However, running more than one VM at a time will cause somewhat jerky performance. I usually leave a few Mac apps running and they are pretty low CPU and memory usage (Terminal, Mail, Calc, etc.) Even running a VM and a higher utilization app, like Firefox with complex websites open, will cause a little lag which is noticeable but not unusable. Even more apps cause more lagging but it doesn't become intolerable for a while.
Note that 2011 and 2012 models have far slower graphics performance - the Intel HD series are just crap compared to the Intel Iris in the current ones.Thanks for your feedbacks. I realize that 4GB would be a limitation for virutual environment. I may settle for an older 2011 or 2012 Mac Mini which will allow me to upgrade the memory as and when required. I just hope than an older generation of cpu and an older version of graphic processor will not cause much performance problems.