Branch 3 separate networks with one switch

So, currently I have three physical ports behind my firewall: 1 for LAN and 2 for DMZ.  The reason that I have 2 DMZs is that I'm using traffic shaping on one of them to limit the bandwidth of internally used systems (like email and defect tracking).  In order to run these three networks, I bought three Dell PowerConnect 2808's, and was planning on just running them in unmanaged mode.  However, I didn't realize how big these things were until they arrived today.  I thought that I could put all three of them on a shelf that only took up 1U, but they're going to wind up taking 1U each.

So, my question is this: instead of using 3 separate 2808's in unmanaged mode, can I get one 2824, and somehow separate the 24 ports into 3 physical networks?  If so, what is this called, and will I take a noticable performance hit in doing it this way?  I've dug through the web console for the 2808, and nothing is jumping out at me as this kind of feature.

Thanks in advance.
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Michael WorshamStaff Infrastructure ArchitectCommented:
What you are looking at doing is called setting up a VLAN:

VLAN :: The Basic Definition

VLAN configuration on a Dell 2824

Configuring Device Switching :: Dell™ PowerConnect™ 28xx Systems User Guide

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msdcdevAuthor Commented:
Thanks mwecomputers.  That's actually the rabbit hole that I'd ventured down since my post.  So, if I'm understanding VLANs correctly, I need 3 untagged, private VLANs?
yes, VLAN will seprate uses by group
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