If you don’t have a monitor plugged into your Mac like my MacMinis, and you need to get some technical informations about your machines (like Model Identifier for max memory), you can do it over SSH / command line, using the system_profiler command.

To get the list of available datatypes, use :

> system_profiler -listdatatypes

To get you model version:

> system_profiler SPHardwareDataType
Hardware:
Hardware Overview:
Model Name: MacBook Air
Model Identifier: MacBookAir4,2
Processor Name: Intel Core i7
Processor Speed: 1,8 GHz
Number of Processors: 1
Total Number of Cores: 2
L2 Cache (per Core): 256 KB
L3 Cache: 4 MB
Memory: 4 GB
Boot ROM Version: MBA41.0077.B0F
SMC Version (system): 1.73f65
Serial Number (system): xxxxxxxxxxxxx
Hardware UUID: xxxxxxxx-xxxxxxxxx-xxxx-xxxxxxxxxxxx

You will find the same data you have in "About his Mac" tool.