Evo T20: Hardware 

Compaq Evo T20


In marketing the Evo T20 Compaq described it as being "Legacy Free". What this actually means is that it has no serial ports, no parallel port and no PS/2 ports for keyboard and mouse. Also there is no standard PC BIOS. However the hardware components are standard.

There are actually a range of models sold under the T20 name - the variation in specification being the amount memory installed and the operating system. To find out what you're getting you need to know the Model Number - which is on the base. Unfortunately I can't find a definitive list of what's what. On the HP website there's a document that provides the following information:

Part NoFlashIntegratedSODIMMOS
238137-00116 MB  none 32MB Windows CE 2.12
289080-xxx 16 MB  32 MB none Windows CE.NET
289079-xxx 32 MB  64 MB none Windows CE.NET
290804-xxx 64 MB  64 MB none Windows NTe with PXE
305253-xxx 128 MB  128 MB none Windows NTe with PX
308791-xxx 192 MB  256 MB none Windows XPe
311334-xxx 256 MB  256 MB none Windows XPe

...but what most people are selling is a 238362-001 (which is what I have) and comes with 16MB flash and a 32MB SODIMM. There is no integrated RAM.

Some more variants were listed on the open-evot20 web page (open-evot20.sourceforge.net/wiki) - now vanished.


The basic specs are:

32MB-256MB (max 512MB)
   Max resolution
1280 x 1024 16-bit colour
4 x USB1.1
H x W x D (mm)213 x 92 x 195 (Excluding Stand)

The circuit board does carry the words (c) WYSE TECHNOLOGY 2001. The T20 a repackaged/rebadged Wyse 3235LE.

Power Supply

psu The Evo's I've seen are often sold without a power supply. This can be an irritant as the power supply connector (DP-003-R) is not one that's readily available on the high street. However an on-line search found me a UK supplier - Toby Electronics - for those who want to fit the right connector to an existing power supply. (Search for "DP Valcon 7.5 Amp Cable Mount Power Plugs")

The Evo T20 requires a 5V supply. The standard Compaq power supply is rated at 4A (see picture right). Plugging my Evo T20 (16F/32M) into a mains power monitor shows an input drain of ~9W when the unit is supposedly off, rising to about 12W when the green LED is on and it's doing something.

As you can see from the label the connections on the plug are:

Pin 1&4:+5V
Pin 2&3:NC


inside If you open the T20 you (may) have the opportunity to increase the amount of flash and RAM. To remove the black cover place your thumbs in the two arcs in the black plastic on the rear of the Evo and push gently upwards. Once the clips come clear you can slide the whole black cover towards the rear and then remove it. This reveals the circuit board (see photo right) and you'll find a SODIMM socket (at the top) and a Smart Media socket (at the bottom). On my Evo these were unpopulated.

RAM: The SODIMM socket takes 144 pin PC133 SODIMM SDRAM memory. You'll find suitable memory advertised on ebay by people who've upgraded their laptops. A 128MB SODIMM can be picked up for £1 plus about the same again in postage charges. So far I've only added 128Mb SODIMMs but I've heard from Troy Wright who has successfully fitted a 512MB SODIMM (Kingston part # KTC-N600/512).

Flash: I've inserted an old 16MB Smart Media card that I have in the Smart Media socket and the system has recognised it. (With the original software loaded you can see this by going to Control Panel/System. It appears as Device 3). To date I haven't actually tried to program/use it. Unfortunately it looks like Smart Media cards of any reasonable size are not dirt cheap unlike Compact Flash cards.


If you've got a soldering iron tucked away somewhere you can dig it out and add a backup battery to the Real Time Clock chip to prevent it losing the time and date every time the Evo is switched off. I haven't done this as yet. Details of how to do it can be found on Karl Mowatt-Wilson's website.


Any comments? email me.    Last update January 2011