Psion Series 5mx Pro

Psion Series 5mx Pro
	A Psion Series 5mx Pro
Specifications
Developer	Psion PLC
Manufacturer	Psion PLC
Type	Clamshell palmtop / PDA
Released	1999
CPU	ARM710T core in Psion's custom "Windermere" SoC @ 36 MHz
Memory	No ROM. Sources quote 24 MB or 32 MB of RAM, part of it reserved to hold the OS image
Storage	Internal RAM disk; CompactFlash slot — also the boot device
Display	640 × 240 touch-sensitive backlit LCD, 16 greyscales
Sound	Speaker and microphone, with a dictaphone function
Dimensions	170 mm × 90 mm × 23 mm
Weight	354 g including batteries
OS / Firmware	EPOC (ER5), loaded from CompactFlash
Predecessor	Psion Series 5mx
Model no.	Shipped with a 16 MB CompactFlash card holding the operating system

The Psion Series 5mx Pro is a rare variant of the Series 5mx that differs in one fundamental way: it has no ROM. The operating system is loaded into a reserved area of RAM from a CompactFlash card, which makes it upgradeable in a way no other EPOC Psion is.^[1]

Mechanically and electrically it is a 5mx. Everything in the Psion Series 5mx pages applies — the same Windermere SoC, the same 640 × 240 screen, the same sliding clamshell, the same screen ribbon and the same hinge hooks.

How it boots

The Pro shipped with a 16 MB CompactFlash card carrying the OS image. The file is called Sys$rom.bin and is about 10 MB.^[2]^[3]

If the machine has no operating system available, it will not simply fail. On startup it asks whether to insert a CompactFlash card containing the SystemRom, or to make a serial connection and load the system over a yModem transfer.^[3]

That prompt is not a fault. It is the single most important thing to know about a 5mx Pro, because a Pro bought without its card looks like a dead or corrupted machine to anyone expecting a normal 5mx.

How much RAM?

Sources disagree. 24 MB and 32 MB are both quoted for the Pro, and part of the RAM is reserved to hold the OS image rather than being available to the user — which is the likely explanation for the discrepancy, though no source states it in those terms.^[3]

A standard 5mx has 8 or 16 MB with the OS in ROM.^[1]

Why it exists

Because the OS is a file rather than a mask ROM, upgrading it is a matter of replacing that file.^[3] On a standard 5mx an OS change means a new ROM daughter board of the right build and language.

It also had an unintended benefit for preservation: because 5mx Pro machines load Sys$rom.bin from a card, copies of the 5mx OS image circulated in a form that could be studied, and it is how the WindEmu emulator and the MAME psion5 driver were developed without access to a ROM dumper.^[2]

Identifying one

It boots from CompactFlash, and says so if the card is missing.^[3]
The screen is often described as slightly brighter and crisper than a standard 5mx's.
Otherwise it is externally a Series 5mx.

Note that a 5mx Pro screen assembly is interchangeable with a standard 5mx one — screens from any 5mx work on any 5mx — which makes Pro machines with dead boards a useful source of parts.

General maintenance

Troubleshooting

Hinge and screen cable

The Pro uses the same chassis, hinge wires and screen ribbon as a standard 5mx. See Psion Series 5mx Hinge Repair.

References

↑ ^1.0 ^1.1 "Psion Series 5", Wikipedia. Source for the existence of the 5mx Pro and the statement that it differed only in having the operating system loaded into RAM and hence upgradeable.
↑ ^2.0 ^2.1 Ash Wolf (Ninji), "\"16 Shades of Grey\" — Building a Psion/EPOC32 Emulator", 27 December 2019. Source for the 5mx Pro's boot-from-CompactFlash arrangement, the Sys$rom.bin file name and size, its structure, and the difference from the standard 5mx.
↑ ^3.0 ^3.1 ^3.2 ^3.3 ^3.4 Community discussion of the differences between the Psion 5mx and 5mx Pro, comp.sys.psion.misc. Source for the absence of ROM, the reserved RAM region, the 16 MB CompactFlash card supplied with the machine, and the boot-time prompt offering CompactFlash or a yModem serial load.

[wp-1] 1.0 ^1.1 "Psion Series 5", Wikipedia. Source for the existence of the 5mx Pro and the statement that it differed only in having the operating system loaded into RAM and hence upgradeable.

[wuffs-2] 2.0 ^2.1 Ash Wolf (Ninji), "\"16 Shades of Grey\" — Building a Psion/EPOC32 Emulator", 27 December 2019. Source for the 5mx Pro's boot-from-CompactFlash arrangement, the Sys$rom.bin file name and size, its structure, and the difference from the standard 5mx.

[grp-3] 3.0 ^3.1 ^3.2 ^3.3 ^3.4 Community discussion of the differences between the Psion 5mx and 5mx Pro, comp.sys.psion.misc. Source for the absence of ROM, the reserved RAM region, the 16 MB CompactFlash card supplied with the machine, and the boot-time prompt offering CompactFlash or a yModem serial load.

[1]

[2]

[3]