I was bitterly disappointed when the companies exited those markets. They still survive -- Psion's OS became Symbian and I had several Symbian devices, including a Sony-Ericsson P800, plus two Nokias -- a 7700 and an E90 Communicator. The OS is now dead, but Psion's handhelds still survive -- I'll get to them.
I have dozens of ARM-powered devices, and I have RISC OS Open running on a Raspberry Pi 3.
But despite my regret, both Psion's and Acorn's moves were excellent, sensible, pragmatic business decisions.
How many people used PDAs?
How many people now use smartphones?
Psion's management were very very smart and focussed on where the money was going. Same as MS did when it developed NT as its next-gem OS, even though even as far as NT 4, most PCs on the market couldn't actually usefully run it.
Same with Acorn. Because RISC OS was a bit of a lash-up, when the mainstream computer market started shipping proper working computers with real multitasking, RISC OS was doomed.
ARM had a very strong early advantage: remarkable CPU performance on an inexpensive chip. Remember it was aimed at desktops. The low-power design was in an effort to get under 1W power usage, so they could use cheap plastic chip packages instead of expensive ceramic ones. The fact that it didn't need a heatsink was an afterthought. This was 1986-1987 when the 80386DX was new.
My first Acorn, an Archimedes A310 (1MB RAM, 20MB ST-506 disk, for £800 used), I bought in 1989. The top-end computer my employers sold was one of these:
IBM PS/2 Model 70-A16.
$6000 without optional extras like keyboard, mouse, monitor or DOS. Trick one out a bit, TEN THOUSAND U S DOLLARS.
My £800 machine was about 4x the raw CPU performance.
That was the selling point at launch, when a 286 with DOS was a normal PC.
3-4Y later, Windows 3 came out, then 3.1. Now, Acorn was selling against comparable-priced 386SX machines with a clunky but functional GUI and a choice of GUI apps... but PDAs are starting to take off, and ARM is a strong contender.
3-4Y later, Acorn is selling against 486s with Windows 95. Now it's a tough sell. There's a lot of elegance, simplicity, raw speed, in Acorn kit, but it's no longer a good value proposition. The RISC PC has a 2nd CPU slot, mainly intended for a 386SX, later 486SLC, processor card so that you can run Windows 3 in a RISC OS window and get at Windows apps.
The RISC PC launched with ARM6 and later ARM7 SoC processors at about 30MHz. About this time, ARM licensed the core to DEC, who made StrongARM: a 200MHz pipelined ARM with onboard cache. It was _dramatically_ faster, although not compatible with 100% of the existing ARM software.
This is what went into the Newton 2000 and eMate, and became a popular upgrade for RISC PCs. This was the last time there was a clear edge in CPU performance and it didn't last long.
IMHO Acorn missed a chance here, and this was the hardware that could have saved it:
A multiprocessor board for the RISC PC with support for up to 5 CPUs.
A single StrongARM was quicker, so it was killed off quickly.
But Acorn could have been the world's first vendor of cheap, mass-market SMP computers -- only RISC OS didn't and doesn't support multiple cores, so they would have had to ditch their OS and use Linux or BSD or something.
Ultimately, it was RISC OS that killed Acorn as a desktop player. Sad but true.
And the ARM was no longer competitive in desktop systems, but it was very competitive indeed in battery-powered kit -- and still is, although not so markedly.
So, Acorn killed its desktops (it never really got far with tablets or notebooks) and focussed on chips, while also selling off its set-top boxes and NCs.
Psion was still very competitive in handheld computers, but the writing was clear on the wall: that PDAs were a dead market segment and smartphones were about to kill them.
So, they split off their OS division and sold the OS to smartphone vendors.
EPOC v5 -- EPOC32 -- was reworked as a smartphone OS, Symbian: effectively the first purpose-designed, open, extensible smartphone OS -- and it pioneered the smartphone market. For years, it was by far the dominant smartphone platform, until [a] Nokia screwed up its project management to a stunningly disastrous degree and [b] Linux came along and killed it, just as it killed proprietary Unix.
Psion products drove tens, maybe hundreds of millions of devices for about a decade hand a half after it stopped selling consumer PDAs. That is pretty good going.
They kept producing handhelds very successfully for years: the NetBook machines switched to the more big-customer-friendly Windows CE, the HC machines morphed into the Workout stock-taking devices. They even ended up buying Teklogix, and the merged company was bought by Motorola Solutions -- the bit left when the mobile phones division was sold off.
That was sold to Zebra Technologies for a whopping $3.4 billion. Not too shabby.
Some of these products should look familiar: