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Rex: The World's Smallest PDA [video]

Rex: The World's Smallest PDA [video]


·October 1, 2022


I have great fun explaining what a PDA is to my students.

'so it's a phone?'

'no because it isn't. Also because it does not have internet connectivity'

'so it's basically a brick? A smart brick?'


Reminds me of a story of a friend of mine, who is a teacher.

He said something like: "Back when there were no computers [...]."

A student raised his hand, and asked:

"But if there were no computers... How did people access the internet?"


900 numbers. Even for kids. Letting your phone company be a 3rd party payment processor, mind-rotting garbage content drawn out as long as possible to maximize revenue, etc. Curse you, 1-900-89-MAURICE!


Jesus Christ what have you pulled out into consciousness from the deepest wells of my mind!


You over-complicate. A Palm practically is just an ancient iPhone with black&white screen and email-only connectivity over an IR or a COM port.

AFAIK there even were late models which could make calls and browse the web.

Smartphones were called "communicators", modem-less models (like what today iPod is to iPhone) were called PDAs.


"Smartphone" was a Microsoft coinage from the early 2000s used to refer to PDAs with phone capabilities running Windows CE.

They didn't trademark the term, so once the iPhone and Androids came out it was applied to them as well.

There are quite a few industry terms like this. "PDA" was coined by Apple to describe the Newton in generic terms. The term "game console" was promoted by Nintendo in the early 90s to prevent clueless parents from calling rival systems "Nintendos"; before that we called them systems or just referred to them by brand name.


> The term "game console" was promoted by Nintendo in the early 90s to prevent clueless parents from calling rival systems "Nintendos"

Too bad that didn't quite work.


I was calling "smartphones" as "smartphones" for sure during the 2000s. In fact, I just looked up the Treo 180 PR (2001ish) and it was calling it a "smartphone". For me "communicator" always meant something looking more like a, well, Nokia Communicator (or with the same form-factor).


The difference between an iPhone and everything that preceded it was not the hardware, but the deals that Jobs struck with the carriers, specifically AT&T, to upgrade their network.


I think a much simpler explanation would be something like "it is like a phone with the SIM card removed - can't make calls or connect to the internet, but can still run its own applications and games" :-P

(the SIM card part would be because it is something the students could do with their own phones -and some might have done at some point- so they'd have first hand experience)


Once I saw a video of kids born in the 2000, they were put a rotary phone in front of them. They could not understand how to dial. We are OLD :)


public display of affection


I would want a modern remake. I would imagine the following updates: Same lo-fi UI, e-ink display, LTE support, UTF-8 MarkDown/ePub reader (but the ePub reader should ignore the book fonts and always the system font settings), Telegram messaging, speed-adjustable OPUS&FLAC audio player, obviously BlueTooth&USB-C.


Modern laptops don't have PCMCIA slots ;-)

I'd like a business-card sized display that could show simple things like my calendar and contacts while being as thin as possible - a small BTLE and WiFi board attached to a .4 mm LiPo battery and an touch e-ink display on top of the whole thing would probably work.


> Modern laptops don't have PCMCIA slots ;-)

That's presumably where the USB-C and/or Bluetooth would come in. Nowadays it wouldn't be all that infeasible to have a flip-out USB-C plug.

Or hell, have the backside be a solar panel, and make the device entirely wireless.


A cellular modem requires a crapload of power though, unless you keep it off most of the time. There's a reason why modern phones have batteries as huge as they do.


There should be a handy physical switch to turn it on/off then.


Related, very thin credit-card sized BASIC computer: I'd like to keep something like that in my wallet


Casio had a watch in the mid 1980s that was smaller with calendar, contact, and notes...


Casio had a whole range of Databank watches that were smaller than this.

What's really fun is you can still buy them brand new for not much money.

I still think that Rex is neat for the time. Would have made an interesting ebook for Project Gutenberg back in the day. Lots of scrolling but you'd always have it with you if you got bored.


The ones they sell today are not as capable as they were in the 90s. I had a few models and loved using them. gives a nice overview of many of the models and their features.

If the ones for sale now were as good as they were in the past or better I would probably get one, mainly for nostalgia.


I'd argue the Fossil wrist PDA is smaller than the Rex.


Absolutely, and it ran a full fledged palm OS.


I loved my Rex... They were amazing and waaay ahead of anything else on the market at the time. Super useful form factor too.


I still do, but I think the only contact that hasn't changed since it was last updated is my mom's home landline ;-)


Looked through the comments briefly and couldn’t mind a mention - but wouldn’t the Fossil Watch PDA have been the smallest, by definition; PDA?

That thing ran a full-fledged version of PalmOS. Way, way ahead of its time. (No pun intended. :P)

If you haven’t seen this little wonder - check it out here:


for some reason I love the idea of these devices.

Obviously the use is now trumped by an always connected phone but i'm thinking of uses where the internet isn't always available. Something like this could come in handy if you kept it in your glove box in your car and it was good at keeping a charge for lengthy periods of time.


> keeping a charge for lengthy periods of time

According to the video the batteries lasted for months - perfect for this "backup device" use case.


What a lovely little bit of kit. I've no idea how useful I would find it (or a more updated version, like a tiny phone, today) but something about it looks incredibly appealing.


I had one, which I kind of regret selling. It had a dinky charm, but when was the last time you needed to look up a contact's details? In the same way Little Black Address Books (and Filofaxes) are redundant these days, the ReX has had its day; remember also that it is a read only device when undocked.


If you are going for small I think these days smart watches are comparable.

There are also credit-card sized smart phones like the Palm (they are thicker than credit cards).


I love these kinds of things. The ubiquitous rise of USB3/USB-C has lead to the complete death of portable tech tools like this. "Thing goes inside my computer" cant happen when theres only cable ports. Imagine this with modern computing power and an e-Ink touchscreen, perfect for being a basic information manager, provided you can sync with the necessary software/clouds (a task that hasn't gotten easier unfortunately).


Could be easily solved with an expansion port that's just a recessed USB male in a card slot with well defined dimensions and tight enough tolerance to ensure the USB always goes in.


Yes, but two problems…

Firstly, without a standard, your just engineering your own solutions and no one else can serendipitously solve your problems for you in the form of a product you can just buy, like the one in the posted article.

Secondly, USB is a much more complicated protocol than the PCI and ISA of days past. Not only that, but the standards are a patchwork of publicly available parts of an otherwise unavailable proprietary whole that the USB standards organisation gatekeeps access too. Yes enough of it is public you can make your own things, but no it’s not the same as things like the ISA bus which is completely documented. You can’t just whip up a cool gadget with logic and some memory then expose it to a computer and then the computer reads it… now you have a bunch of embedded device work to do so your gadget can initialise its side of the communication protocol and respond to whatever software you write sending it interrogation messages over whatever protocol you end up using. So much more complex.

I did a bunch of research recently on computer interface busses while looking for a “slot bus” to build something out of embedded hardware modules that were individually responsible for their on-board logic but needed a common backplane for power and inter module communication… seems simple right, well no… it turns out the last fully open well documented “passive backplane” bus was ISA bus. So I’ve had to begin pondering how to build my own solution, which will probably just be some kind of SPI which leads me to my current lament of standards other than USB, when everything is a USB device, if your use case is for something other than USB then your just out of luck.


That's what I was thinking, some kind of USB-D card standard that specified exactly where the port goes. It would be extra cool because it could also serve as a battery format, just make a power bank in that size.

USB 2.0 and 1.1 are trivial solved problems in practice. They're built into so many chips now, and it's far easier to work with in terms of PCB design. Stuff like the ESP32-S2 or even the soft implementations in 8 bit micros are really good and just work, plus you have the possibility of fully driverless stuff pretending to be storage, keyboards, midi, ethernet, etc, and it's all just as easy as any other Arduino lib, no protocol understanding needed.

It's true that you can't do dumb passive stuff with it(Although if you really wanted to you could use a dedicated USB to SPI/I2C/GPIO whatever chip and have the PC emulate whatever you want), but that doesn't really hold back products, things are just done differently.

It sucks for anyone trying to make gadgets that aren't just a microcontroller plus code, but there's so many possibilities with the new style that it's worth learning.

For hobby tinkering type stuff and exploring stuff outside "A PC that talks to a MCU", yeah, it's not really a supported use case.


I2C perhaps? Fewer wires than SPI.


Could possibly replicate this with the framework notebook and it's expansion card standard:




looks like it fits in a PCMCIA slot


Yes. That was one of the ways to plug it in to sync. I had one for a while and carried it around in my wallet.


Mine came with a serial-based desktop unit. The laptop tended to scratch the paint.