My machines are 2 old Sun Workstations running SunOS 4.1.3 and FreeBSD (one is a SUN 4/110, and the other is a SPARCStation 1+), a home built (as in, I built it from bits of discarded computers I found in skips in Central London) Pentium P75 (clocked at 90MHz) Multimedia PC, a Pentium 266 Laptop, a Celeron 300 Laptop, a 450 Mhz Pentium II with 128 Mb of RAM with Red Hat Linux 6.1 with Gnome, and 2 1 GHz+ dual booting Windows 2000 / Linux boxes. All computers are networked via 10baseT or 10/100baseT hubs and a 24-way 10/100baseT Ethernet Switch.
I am currently building a server into an old Dell server case. The case was designed for AT motherboards, so a few modifications were neccessary in order for it to take a more modern ATX motherboard. Unfortunately, the layout of external ports (serial, parallel etc) on an ATX motherboard is completely different to that of an AT motherboard, so some major changes are underway to the internals of the case. The case has 10 x 5 1/4 inch drive bays though, which is ideal for a data server. I'll probably use an ABIT KT-7A RAID ATX motherboard, simply because I used an ABIT KT-7A ATX motherboard for the last PC I built, and it has been a decent enough motherboard.
Building hardware is nowhere near as hard as people may think. It is not really any cheaper than buying a complete system however, but enables you to gain a much greater insight into how your computer works, and can enable you to tweak your computer's performance. I have lost count of how many changes I've made to my PCs and Sun workstations - most of them have worked, however, failures can be fairly catastrophic, as some of the fried motherboards and add-on cards I have amassed would seem to suggest. I have prepared a couple of web pages to act as pointers for those who may be curious about various hardware modifications, the pages cover the hows and whys of cooling computers and interfacing a Linux laptop to household appliances.
Additionally, on the move, I use a Sony Vaio Z505. This laptop really is the business; Celeron 300 CPU, built in 10/100 BaseT networking, built in V.90 56Kps modem, 12.1" TFT screen. basically, the perfect Linux laptop !
I also use a special, modified HP Omnibook 800 dual booting to Linux and Windows-95 (allows cgi/java/c hacking on the road), and a Palm V. Why is this Omnibook 800 special ? Well, there aren't many laptops out there that have been autographed in gold marker by Alan Cox (Yes, the Alan Cox of Linux fame !). How is the Omnibook 800 modified ? Well, I broke the screen, so I rehoused the entire thing in an alumnium flight case, so now it acts as the launch control computer at various rocket launches.
Previously I used a Toshiba Libretto and a REX - the Toshiba Libretto has now been relegated to controlling various external hardware systems. Just in case it's helpful to others, I have written a separate page detailing the Linux based HP Omnibook 800, and the installation of Linux on it.
Currently, I use a Compaq iPaq HS3630 with a TDK bluePAQ Bluetooth expansion pack with a built in Compact Flash socket. This set up really is about as good as it gets for a PDA, as far as I am concerned. It does everything I need in a PDA, and even runs the same rocketry related software that I use on my laptop and desktop PCs.
My full mobile set up generally consist of the Compaq iPaq, the iPaq TDK bluePAQ Bluetooth expansion pack and a CompactFlash card to store maps, together with an iSun Solar Panel for remote power recharging, a Garmin eTrex GPS which plugs into the Compaq iPaq via a null modem, and my mobile phone. This generally provides for most remote connectivity needs, as well as autonomous power and remote spatial location needs.
Before the Compaq iPaq, I used a Palm V for a few years - an absolutely superb little PDA, with excellent battery life.
Originally, I used to use an Apple Newton MessagePad from 1995, and then a Psion 5 from 1997, both of which I connected at base with the PC (at home). In the field, I powered the Newton and the Psion 5 off a combination of rechargeable batteries and solar panels. I will probably start using the Psion 5 again when the Linux port for it becomes more stable.