Recently, I've given myself the project of setting up a good high-power desktop computer that would fit within carry-on limits. Here's my documentation on what I did, why I did it, and how you can do it too (if for some strange reason you want to).

Why did you want a desktop?
Desktop computers have much better cooling, and longer life. They are cheaper for the same power, and can be easily (and cheaply) upgraded.

Why did it have to be carry-on sized?
I didn't need a machine to use on the plane (I have a little netbook for that), but wanted a high-powered gaming machine that would be easily portable. I travel between the US and the UK a lot, and will likely be moving this computer between the two places at least once every few months. I would prefer to have a single

Okay, so you wanted a high powered computer. Why not just get a top end laptop, spend a little extra, and save yourself a lot of trouble?
Well, I like that I can actually repair/upgrade a desktop (as opposed to the impenetrable workings of a laptop). I know it's bulky, but honestly, I don't mind that so much.

Are you stupid? This is an awful idea.
No. Also, shut up. It's fun . I like a good project, and this seemed like an interesting problem to solve.

Fine, go on.
Thank you.

So, did you build the whole thing from scratch?
I thought about it, but I like the convenience of getting a pre-built system and modifying it, rather than installing everything myself. I decided to buy a stock model and then tweak it.

What are the rules for carry-on desktops?
I checked with TSA, and desktops are not on the prohibited items list. I then called Continental's Silver Elite phone line. They confirmed that there's no problem with bringing a desktop computer in carry-on, provided it fits within the carry-on size limits (14 in x 9 in x 22 in). YMMV with other airlines.

What base did you use?
I've had pretty good experience with Best Buy's customer service. Returns are easy, and their pricing is usually pretty good.

I started off with an HP Pavilion Slimline 5310y ($459). The form factor is very small, and it looked like a great candidate. It had an open PCIe slot, so I could put in a new graphics card (note that it is a small case, so I had to use a low-profile card). However, there were two MAJOR problems. First, the power supply is only 220W. No big deal, I could just replace it with a better PSU. Unfortunately, the Slimlines use a proprietary long form-factor PSU (not standard ATX/mATX) which can only be upgraded with a 270W model. I had to return the computer to Best Buy, because it just couldn't be upgraded to do what I wanted.

My second choice was the one I ultimately went with, the Asus Essentio CM5571-BR003 ($469). It fits within the carry-on measurements...just. 15.5" x 14" x 8" (versus 22 x 14 x 9 limits)

This was a much better choice for several reasons. It has 6GB of RAM, with an open DIMM (rare on most off-the-shelf computers) so cheaply upgradeable to 8GB, and potentially maxed out at 16GB RAM. Its PSU was only 300W, but was standard ATX, so cheaply switched out. It has only a single PCIe slot (a down side), but this isn't really a big problem. The case has good ventilation, and has two available 5" bays plus a spare HDD rack internally. It uses a Socket 775 CPU, so plenty of scope for upgrading there too as my needs change. This unit would make a great base for anyone looking to incrementally upgrade a system over time.

What did you do to improve performance?
I made three changes to the machine. First, I swapped out the PSU for a 550W model from BFG ($55 in the shop, you can find it for $50 on Newegg). BFG make good quality PSUs, and buying one that would beat my power needs give me scope to upgrade, and also ensures quiet running (it modifies fan speed based on load). Their modular cabling is well designed, avoids clutter, and improves airflow.

Second, I installed a new graphics card. I chose the GTS 250 from Sparkle. This is a low-profile card which I originally bought for the Slimline. It has HDMI and DVI outputs. Admittedly, it is a bit of a power hog. Normally, you need two 4-pin plugs to power it, but the BFG PSU has a dedicated cable to run it (so far, no problems there). That said, it's boosted my graphics performance to really stellar levels, and relieved any possible strain on the RAM (though with 6GB, I won't be taxing it anytime soon).

Finally, I replaced the case fans with some cheap silent fans from MicroCenter. It runs barely above a whisper when on (have yet to test it gaming, but I suspect that the PSU won't be taxed too heavily).

Final cost?

$469 for the system
$100 for the card
$50 for the PSU
$10 for the fans

$650 including tax total

Configuring the Dell Inspiron 580 similarly costs $729. That includes a much lower-tier graphics card, a weaker CPU, a weaker power supply (300w) and no fan upgrades.

So, are you happy now?
Yeah, I had fun. Thanks for asking. Are you alright? You seem a little crabby.

I'm fine. I just forgot about my tea and it got cold. I hate cold tea.
Then just put it in the microwave.

Oh! Thanks
No problem.

I remember back in the olden days of 1983 taking one of the original Compaq portable's on planes regularly. It was kind of annoying to carry around. Probably heavier than what you have built.

http://oldcomputers.net/compaqi.html

It fit in most overhead bins of the era except the BAE146 bins near the wing and was sometimes pesky on TWA L1011 with the vertical bins.

Pics or it didn't happen(I mean I want to see this puppy in the bag!)!
But seriously, this sounds like a good idea for people who don't live in one place for more then a couple weeks that want their Crysis without getting a super expensive laptop...and its upgradable and reparable as you said!
And what do you use for a monitor?

A small bank I used to work for had one of the Compaq and also a KayPro I:

http://www.obsoletecomputermuseum.org/kaypro-1/

My memory is sketchy, but I think we used to run a multi-user version of CP/M on the KayPro called TurboDOS.

In comparing it to a laptop, didn't you leave out one small advantage to the laptop? Namely, you can use it on a plane for work or for fun. Also, like another poster wondered, where are the pics in this day of easily posting photos, that'd seem like the way to show off your workmanship (which still doesn't make it usable inflight).

With how small they make LCDs you caneasily fire that thing up if there is power outlets on your trip. I would think you could just carry the box around bagless. It would def make it easy to spot it someone tried to steal it. I would also def expect a good hand inspection at security.

Other thing I would consider is if it will fit under and rj seat as you wouldn't want to be gate checking that.

$3590!

I think one of the reasions desktops have a longer life is they don't move. Laptops are constantly droped, shaken, coffee or other liques spilled on them.

Desktops just sit there.

I did this. The GTR Tech GT3 SFF ATX Case is full ATX, can accomodate quite huge video cards (double slot PCI Express x16) and does fit in a carry on -- again I did it.

Size in inches: 15.4 x 4.25 x 12.5

Hey guys Thanks for all the responses, interest and heckles!

I will post photos of me with it at the airport when I fly with it.

One slight hiccup is that I will have to fly my first leg on a COEX RJ145...very limited bin space. Hopefully I can cram it in up there, or squeeze it under seat (I've grabbed a seat on the BC side to avoid the funny shaped underseat space of the A seats on those planes.

To answer a question:

I'll be using various LCDs and HDTVs as monitors in the different places I go. I won't be brining the display with me.

Sweet, that's what I want to hear
Aww...I was expecting something like a carry on 19 inch LCD

What's the total weigh on this one? And what carrying case did you get?

Well, good news and bad news. The good news is that I got the airport through security without so much as a dirty look. They didn't even ask me to take it out of the case! The bad news is that I forgot to take photos. Yes, I am an idiot.

Carrying case was my trusty old MEI Convertible which, so far as I know, is no longer made. I love that backpack dearly.

In 1983. That's $7800 in 2010 dollars.