WS-C3560-48PS-S Catalyst 3560 48 10/100 PoE + 4 SFP IPB Image
S -> Standard Multilayer Software Image (SMI)
48 10/100 PoE -> 48 10/100 ports with Power over Ethernet
4 SFP -> 4 x Small Form-factor Pluggable ports
IPB Image -> IP Base feature set image.
WS-C3560-48PS-E Catalyst 3560 48 10/100 PoE + 4 SFP IPS Image
E -> Enhanced Image (EMI) installed
48 10/100 PoE -> 48 10/100 ports with Power over Ethernet
4 SFP -> 4 x Small Form-factor Pluggable ports
IPS Image -> IP Services feature set image.