Tom Stepleton

@stepleton.bsky.social

1632 Followers 98 Following

AI research engineer, glider pilot. Apple Lisa power user. @stepleton@oldbytes.space on Mastodon. Most of my posts will be about old computers; occasionally I'll mention flying.

Part of the cover page for Foster et al.'s "An Introduction to the FLEX Computer System". My talk title is superimposed on top: "RSRE Flex: reviving an innovative, remarkably odd British operating system that almost nobody knows about"
Login splash screen for the RSRE Flex computing environment. The Flex logo is shown alongside "Evaluation Kit"; additional text shows a crown copyright notice, a solicitation of feedback, and basic instructions.
My table at RetroFest: a rather austere looking affair with the PERQ system unit itself hulking on a tabletop with its covers off. The keyboard and mouse-like pointing tablet are next to it, then a 19" LCD monitor that looks small in context. The monitor is showing a moment from the Accent demo program that includes a drawing of a robot arm. On the other side of the system unit, the rear panel lies flat on a box, the hard drive (emulator) lying flat instead of orientated vertically as it was intended to be. In front of the PERQ are several stickers bearing the logo of Three Rivers Computer Corporation. Above the display is a whiteboard sign described in the next image.
The Three Rivers Computer Corporation logo: a stylised R patterned after circuit board traces and the words "Three Rivers Computer" in a futuristic bold sans-serif typeface (probably ITC Avant Garde Gothic).
Proof of life: my PERQ 2T2 running RSRE Flex. Flex never had a fancy graphical demo: this is just the login screen.
Proof of life: my PERQ 2T2 running the POS SIGGRAPH demo. A high-resolution monochrome video display shows the PERQ Systems Corporation logo, the word PERQ in large letters, and the tagline "The definitive graphics workstation".
Proof of life: my PERQ 2T2 running the PNX graphical demo. A high-resolution monochrome video display shows a set of overlapping windows with line and raster graphics and with sales text extolling the features of the PERQ 2.
A bare window on a spare 1980s graphical interface bearing the message "hello retrofest 2026"
Two DIP IC packages sitting on a blue anti-static mat. The 20-pin device is a 74S225 16x5 FIFO and the 16-pin device is an AM25S10 4-bit shifter. Both have big Xs written on them in yellow paint pen.
A still from a video on the Technology Connections YouTube channel. The presenter Alec is sitting at his usual desk with a device that makes the bell noise heard at American railway crossings. The closed caption visible on screen says "But almost anything can be fixed if you're patient enough."
A hardware debugging scene: from left to right, a Tektronix TLA714 logic analyser (a big squat box with an LCD computer display), a PERQ 2T2 workstation with the covers off and the EIO board jutting out from the front (I'm using bus extenders for easier access to the ICs), and an oscilloscope. Wires snake everywhere to connect the test equipment to the guts of the ailing PERQ.
An 8" floppy disk rides "hammock-style" on a pair of wires slung inside of a smoked perspex box with a backlit indicator panel.
Two Farallon EtherMac 10BASE-T MAUs with their AAUI connectors plugged into small circuit boards with AUI plug connectors. These circuit boards are the AAUI-to-AUI adaptors described by the project linked in this post.
A trio of floppy disks: a big 8" disk, a fairly ordinary 5.25" disk for PCs, and an Apple FileWare (aka Twiggy) disk.
Picture of a citation at the end of a paper. The citation says: 15. "Flex and the ICL Perq2" M.Stanley. University Computing Vol 8, No 2, Summer 1986.
The display from a broken Sinclair ZX Spectrum+ computer: inside a thick green border, eight alternating black and white vertical bands with a few small, coloured squares arranged on the left-hand side.
A circuit board with two DIP ICs and some passive components connects a VGA cable and two DIN-5 cables (top) to a DIN-4 cable, a DA-15-terminated ribbon cable, and a 75-ohm coaxial cable (bottom). The bottom cables go to a PERQ T2 workstation; the top cables go to mouse, keyboard, and display.
The camera sweeps along a rank of vertically-orientated circuit boards that use "cordwood" construction: axial-leaded components like resistors connect adjacent circuit boards like the rungs of a ladder. This kind of construction trades serviceability for density. Amidst the passive components, transistors in metal cans seem imprisoned. After completing the slow sweep, the camera draws backwards and upwards quickly to show the Olivetti Programma P203 that used to house the circuit boards.
A group of people walk a slender aircraft with long wings down a tarmac taxiway, all silhouetted by the rising sun ahead of them. A shallow mist rises off of the airfield's grass surface.
An assembled RC2014 Zed Pro modular Z80 hobby computer, which comprises a backplane about the size of a paperback book with playing-card sized component circuit boards plugged into it vertically. This particular Zed Pro is the limited-edition Pride kit, where the component boards are coloured so that they form a rainbow when arranged in the backplane. The computer rests in the hands that assembled it, which here are sporting some fairly long, blue-varnished fingernails. All of the electronic components, including dozens of resistors, headers, and IC sockets, were placed and soldered with the fingers and fingernails shown.
A monochrome graphical display from an old computer workstation. In a large window at the centre of the display, a Smalltalk-80 session can be seen, with a browser window partially occluded by a System Transcript and a System Workspace window.
A black and white screen image of a graphical desktop with several windows. One window shows a clock, another a bar graph with the bars bouncing around, another a graphical diagram of a heterogeneous computer network with many PERQs on it, and a final slide describing various attributes of PERQ Networking, viz. PERQ Networking * 10 MBit Local Area Network - ECMA 72 Transport protocol - File Transfer - Remote Printing/Plotting * Wide Area Networks - IBM 2780/3870 emulation - ICL-C03 protocl - Asynchronous Terminal Emulation - uucp
Splayed out on a wooden floor: a covers off, partially-disembowled PERQ 2T2 under-desk workstation computer. Wires snaking out of the PERQ attach to a solderless breadboard which is then attached by a sheaf of probe leads to an old Tektronix logic analyser nearby. It looks a mess but atop it all is a 19" monitor showing video coming out of the PERQ. The machine is running and shows the diagnostic code 255 on a 7-segment display.
Top, the Inmos logo: the word Inmos to the right of a black circle with a grid of white squares inside. It's meant to recall a silicon wafer full of integrated circuit dies. Inmos was a legendary British semiconductor manufacturer who invented the transputer architecture, an innovative also-ran. Bottom: the logo for Imo's Pizza (an infamous St. Louis chain) next to an image of a circular pizza cut into squares, as Imo's does.
A fraudulent Jupiter ACE 4000 and Jupiter ACE 4000 manual: it's actually a regular Jupiter ACE in an ACE 4000 case. Both the ACE and the ACE 4000 were inexpensive, book-sized home computers that used the Forth programming language instead of BASIC. Forth uses a postfix (aka "reverse Polish") notation, which is the joke behind the strange word order in the post.
A parody clone of the cover of a Ravensburger puzzle box, advertising a "Laserburger Puzzle" with "up to 570" pieces and "Crummy Laserburger Qualtiy [sic]". The puzzle claims to have "Arduousclick Technology", referencing the "Softclick Technology" of actual Ravensburger puzzles. The puzzle itself appears to be a halftone image of a bunch of potatoes, and helpfully the original potato image appears at the bottom of the box art alongside the text "it is potates".
A circuit board with a collection of DIP ICs from the early- to mid-1970s, with characteristic "wavy" hand-drawn circuit traces. Closest to us is a ceramic-package MC6800 with a gold cover, but behind it is a rank of five MC6800 PIAs made by AMI in white ceramic packages with grey "spider leg" traces extending from the chip die to the DIP pins. If only microchips were packaged like this today...
A monochrome computer display with overlapping windows: one with the ICL logo, another with a "Mystify"-style bouncing lines demo, another showing a directory tree, and another boasting about the PERQ 2's floppy drive and hard drive storage options.
The screen of a logic analyser showing numerous signal traces. A circled area on the left shows the hexadecimal digit C going into the 74S225 memory, while a circled region on the right shows the hexadecimal digit 4 coming out of it. The binary pattern for C is 1100, while 4 is 0100. A 1 bit has been lost.
Close-up of a computer display showing text-filled areas and blank areas with graphical corruption. The nature of the corruption is lots of black vertical bars as well as vertically-aligned dots. For the curious: the PERQ has special hardware for moving data around in memory called a "blitter". It's especially useful for drawing text to the screen, since you can store characters in other areas of memory and then copy them to the display each time you need to show a new letter. But the blitter temporarily stores the data in a 74S225 as it does its copying, and if the 74S225 doesn't store data correctly, you get corruption like this.
Excerpt from the PERQ EIO board schematic showing four 74S225 16-by-5-bit FIFO ICs that connect the PERQ memory data bus to the Z80 data bus. Those are a 16-bit and an 8-bit bus respectively, so the analogy of a two-lane road becoming a one-lane road is pretty apt. The bytes must take turns, and the 74S225s gives bytes a place to wait as they zipper-merge onto the data bus. There are four 74S225s here, but that's because each one is only five-bits wide: you need two of them to store a byte. (Each one has an unused bit.)
In a modified clip from Sherlock Jr (1924), Buster Keaton rides a driverless motorcycle on its handlebars and narrowly avoids getting run over by a train (repeatedly).
Just more text describing the difference between the bytes D3 and 53, as far as a Z80 is concerned. D3, which is 11010011 in binary, is written as "OUT (n),A" in Z80 assembly language and means (simplifying) "emit the A register's contents on I/O port n". OUT instructions are what the Z80 uses to send configuration commands to U159. 53 meanwhile is "LD D,E" and means "move contents of the E register into the D register", which is some data-shuffling internal to the Z80 that doesn't involve U159 or any other external device in any way.
Double-spaced lines of text showing a hexadecimal representation of the program code that the Z80 should be running. In the space beneath the line, corrupted digits are noted. Extra info for you, the ALT-tag reader: there are also pipe characters that happen to mark "seams". The PERQ uploads program data into the Z80 in 31-byte chunks, and the pipe characters show the boundaries between those chunks.
The PERQ's EIO board, which handles all I/O for the PERQ except for the video display. It's a large circuit board with over 200 separate DIP ICs on it. Arrows point to the board's Z80 microprocessor as well as U159, the 8254 programmable interval timer that generates the clock pulses for the mouse.
A closeup of my electronics workbench exhibit at the Centre for Computing History's Retro Computer Festival in November, 2024. The logic analyser is displaying a schematic (it's basically a Windows 2000 machine, after all). The oscilloscope is on but idle. The PERQ has its CPU board extending outward from its installed position, showing many dozens of chips. Directly in front, on the anti-static mat, illuminated by an overhead lamp, the "solder side" of the EIO board, the large circuit board that handles nearly all of the PERQ's I/O. Some thin, barely-visible "flying leads" have been tacked to locations on the board, providing electrical access to signals that will soon be measured on the logic analyser. There was a whole exciting festival going on around me when I snapped this photo, but it was easy sometimes for just this scene to fill my entire field of attention. Extra for ALT tag readers: at this stage we are pursuing a red herring, investigating whether incorrect address decoding logic is preventing the Z80 from sending signals to U159. This was not the problem...
A person in a blue plaid shirt and beanie gazes at my electronics workbench exhibit at the Centre for Computing History's Retro Computer Festival in November, 2024. Arrayed on a table atop a blue anti-static mat: a logic analyser with mouse and keyboard, a multimeter, an oscilloscope, and of course the PERQ itself with most of its covers off. Atop the PERQ, a screen and keyboard plus a whiteboard proclaiming "Tom vs. PERQ" and the goal of fixing the mouse.
An excerpted page from the PERQ schematics, with highlights pointing out U159, the Intel 8254 programmable interval timer, and the TABLET CLK clock signal that it generates. The skew away from the vertical is present in the scanned schematics document; it's not artistic license, in other words...
The PERQ's "mouse pad": a fairly empty-looking, square circuit board with a few clusters of DIP ICs at its upper edge. Elsewhere, a grid of circuit traces spreads across the otherwise-bare board. Current flowing through these traces generates magnetic fields that are detected by a coil inside the mouse.
An electronics workbench with a PERQ 2T2 computer resting atop it: its system unit is not quite as large as the kind of refrigerator that fits beneath a desk. Most of its covers are removed. Highlighted in the image is the PERQ's three-button mouse. Text on the image says, "Issue: mouse not functioning, other peripherals seem to work ok".
Close-up of an Apple Lisa computer's display as the LisaDraw program sends a festive card design with a Christmas tree to a dot-matrix printer. The Lisa's print dialogue is verbose. It tells the user that print spooling is available: that is, the user can dismiss the dialogue and do other work while printing continues. But it also points out that if the user does this and then at some point "hear[s] a whistle", they should reopen the print dialogue. (The Lisa's "whistle" is a rising bloopy sound that the Lisa makes if printer trouble occurs, like running out of paper. I only know early versions of the Lisa Office System to make this sound.)
A notebook with dense, tabular notes in fine writing is propped up by an oscilloscope resting atop a PERQ computer system unit. At the bottom, the PERQ's diagnostic numeric display reads 014, which means the computer couldn't boot from the hard disk.
The cartoon character Hank Hill from the TV show King of the Hill gives a wary eye to a desktop PC with a CRT monitor perched atop.
Screenshot detail of text from POS attempting to boot. Letters no longer have random vertical bars, but pixels and other parts are missing. The complaint about System.6.A.ZBoot is not unusual or relevant here.
A fancy chip testing gizmo, looking like a stack of circuit boards, tests a 74S225 FIFO IC. The display says “78225 Test failed. Memory failed. Again?” The smoking gun…
A modern(ish) LCD display shows a white screen with text on it from the initial boot of PNX announcing version numbers and sundry other information. Blank areas of the screen have vertical “pinstripes” made of tiny dots, and letters are corrupted with things like random vertical lines.
A pair of solderless breadboards holds a collection of jumper wires and passive components along with cable ends that extend out of shot and a pair of DIP ICs (a 74LS123 and a 74S241 for anyone curious).
A yellow trace on an oscilloscope display has the hallmark sign of a monochrome video signal: an oscillation between mostly high and occasionally low signals with barcode-like spikes on the high part. The signal has lots of overshoot which is just due to my poor probe grounding; not really relevant here.
An oblong black panel a bit bigger than a deck of cards. There is a big red power switch at right. At bottom left is a black button with the word “RESET” printed above it; at top left, beneath the word “DIAGNOSTIC”, is a three-digit 7-segment LED display that reads 231.
The photo of the PERQ EIO circuit board from earlier with a small 8-pin DIP outlined in red. A blown-up picture of the IC is superimposed over the image, revealing it to be an SMC-branded FDC9216B.
The photo of the PERQ EIO circuit board from earlier with an SRAM IC outlined in red. A blown-up picture of the IC is superimposed over the image, revealing it to be a Mitsubishi-branded M5M2167P.
One 8” and three 5.25” Micropolis hard drives borne by a furniture dolly. All of them look impressively bulky. The three smaller drives are in anti-static bags.
A boxy Tektronix TLA714 logic analyser (basically a box with an LCD on the front) is in the foreground. Four thick cables full of probe wires snake out of the box and back into the PERQ in the background.
An oblong black panel a bit bigger than a deck of cards. There is a big red power switch at right. At bottom left is a black button with the word “RESET” printed above it; at top left, beneath the word “DIAGNOSTIC”, is a three-digit 7-segment LED display that reads 010.
A large oblong circuit board with over 200 small- to medium-sized DIP chips fitted. A large square of the circuit board touching the top and left sides contains regularly-spaced chips: these are the DRAM ICs. This board is responsible for the PERQ’s main memory and for generating video. Look closely to find the bodge coaxial cable.
A large oblong circuit board with over 200 small- to medium-sized DIP chips fitted. Both sides have card edges with gold fingers. Some of the chips on the left side are ceramic packages with gold lids: these are the memory chips that hold the program-supplied microcode.
Three Rivers Computer Corporation logo: a stylised letter R resembling circuit-board traces and the words Three Rivers Computer in, again, a very 1970s font.
Diagrammatic cutaway image of a PERQ 1 workstation computer. A monitor and tablet sit atop a desk; beneath the desk is a brown, boxy system unit with the cutaway showing a hard drive, circuit boards, and other gubbins. Everything is looking very late-1970s. Image copyright UKRI Science and Technology Facilities Council. From https://www.chilton-computing.org.uk/acd/sus/perq_papers/perq_external/p005.htm
A PERQ 2T2 system unit with its covers off. The machine is operating and a 3-digit LED readout at top right says 999. Circuit boards with ribbon cables exiting are visible; so is a Gotek floppy drive emulator. At right, the PERQ keyboard (taking layout cues from the VT100 keyboard) and behind it a LCD monitor showing black text on a mostly-blank white background.
A Tektronix 136-channel logic analyser with probe wires snaking over to a PERQ 2T2 graphical workstation with its covers off in the background. The PERQ is quite the repair challenge!