Sabadaço do Garbage Collector de Retrópolis
https://retropolis.com.br/2025/04/05/sabadaco-do-garbage-collector-de-retropolis/
#MundoRetro #Commodore #Fax #FitaCassete #GarbageCollector #GravadorCassete #KenShirriff #Lotus123 #mainframe #MSDOS #PDP11 #Pentium #UNIX #Windows98
"[I made] a histogram to show the distribution of wealth in the United States. It turns out that if you put Elon Musk on the graph, almost the entire US population is crammed into a vertical bar, one pixel wide. Each pixel is $500 million wide, illustrating that $500 million essentially rounds to zero from the perspective of the wealthiest Americans."
http://www.righto.com/2024/10/wealth-distribution-in-united-states.html?m=1
Ken Shirriff arregaça o Intel 80386
https://retropolis.com.br/2024/02/11/ken-shirriff-arregaca-o-intel-80386/
Uma coleção de notas RISCadas
https://retropolis.com.br/2023/10/24/uma-colecao-de-notas-riscadas/
#MundoRetro #AlphaAXP #IntelI960 #KenShirriff #PowerPC #RISC #RS6000 #WindowsNT
[Ken] Looks at the 386 https://hackaday.com/2023/10/16/ken-looks-at-the-386/ #Retrocomputing #kenshirriff #80386 #intel
16 Kbit DRAM Gives Up Its Secrets https://hackaday.com/2023/09/26/16-kbit-dram-gives-up-its-secrets/ #Retrocomputing #kenshirriff #4116 #dram
This came up (tangentially) on Hacker News today, but this video of Ken Shirriff going over the Xerox PARC Alto is fascinating.
Finding Undocumented 8086 Instructions Via Microcode https://hackaday.com/2023/07/17/finding-undocumented-8086-instructions-via-microcode/ #undocumentedinstructions #Retrocomputing #kenshirriff #8086
Great new reverse engineering on the 8086 of something we now take for granted: division by #KenShirriff - https://www.righto.com/2023/04/reverse-engineering-8086-divide-microcode.html
virtual HIMARS teardown https://twitter.com/kenshirriff/status/1552723519087198208 /via #kenshirriff #himars #fckptn
Can You Hear Me Now? Lunar Edition
Despite what it looks like in the movies, it is hard to communicate with astronauts from Earth. There are delays, and space vehicles don't usually have a lot of excess power. Plus everything is moving and Doppler shifting and Faraday rotating. Even today, it is tricky. But how did Apollo manage to send back TV, telemetry, and voice back in 1969? [Ken Shirriff] and friends tell us part of the story in a recent post where he looks at the Apollo premodulation processor.
Things like weight and volume are always at a premium in a spacecraft, as is power. When you look at pictures of this solid box that weighs over 14 pounds, you'll be amazed at how much is crammed into a relatively tiny spot. Remember, if this box was flying in 1969 it had to be built much earlier so there's no way to expect dense ICs and modern packaging. There's not even a printed circuit board. The components are attached to metal pegs in a point-to-point fashion. The whole thing lived near the bottom of the Command Module's lower equipment bay.
The processor, or PMP, played a key role in multiplexing different streams in different configurations and passing them to (and from) the onboard S-band transmitter. Inside the box, [Ken] found four subassemblies nicely labeled and connected to a thin backplane. Along with discrete components, the modules also employed off-the-shelf assemblies that predated ICs and offered functions like filters or oscillators in one convenient package.
One thing that further complicated the design was the need for redundancy. For example, there are two switching regulators inside -- yep, a switching regulator in a piece of gear from the 60's -- and the crew could select between the two power supplies.
[Ken] takes us through each module. The voice and data detector module extracted voice on a 30 kHz FM subcarrier. There's also a bi-phase modulator, voice clipping, and a relay module to pass signals from the lunar module back to Earth.
If you want a closer look at the Apollo comm system, [CuriousMarc] has a series about it and was part of the group and stripped down this PMP. Radio signals are fun, of course, but the best footage came back as film. However, modern technology has sharpened up some of that old footage.
The Apollo Digital Ranging System: More Than Meets The Eye https://hackaday.com/2022/04/25/the-apollo-digital-ranging-system-more-than-meets-the-eye/ #kenshirriff #rangefinder #radiohacks #apollo #radar #space #nasa #jpl
The Apollo Digital Ranging System: More Than Meets The Eye
If you haven't seen [Ken Shirriff]'s teardowns and reverse engineering expeditions, then you're in for a treat. His explanation and demonstration of the Apollo digital ranging system is a fascinating read, even if vintage computing and engineering aren't part of your normal fare.
The average Hackaday reader should be familiar with the concept of determining the distance of a faraway object by measuring how long it takes a sound or radio wave to be reflected, such as in sonar and radar. Going another step and measuring Doppler Shift - the difference in the returned signal's frequency - will tell us the velocity of the object relative to our position. It's so simple that an Arduino can do it. But in the days of Apollo, there was no Arduino. In fact, there were no Integrated Circuits. And Apollo missions went all the way to the moon- far too distant for relatively simple Radar measurements.
The TPAC contained transistor logic for the ranging computer
How could range (distance), position, and speed then be measured? The answer is one that [Ken] aptly describes as fractal: Each layer of complexity hides beneath it another layer of complexity. Using equations dating from 3rd century China as well as cutting edge weak signal telemetry, Apollo engineers devised a complex but workable system that used an S-Band transponder to take data transmitted from a powerful ground station and send it back on another frequency. One great hack was to use Phase Modulation to encode the downlink instead of Frequency Modulation so that Doppler data gained on the uplink wouldn't be lost on the downlink.
By knowing the precise position of the ground station and the very large parabolic antennae, not only could the distance and speed be measured, but a good estimation of the spacecraft's position in 3d space could also be had.
From the use of delay line memory to aggregate weak signals to a state machine computer made up of discrete transistor logic, all the way to the cutting edge transponder on the Command Module, the Apollo digital ranging system is an excellent example of great hacks coming out of a program with tight technical constraints.
We highly recommend giving [Ken]'s blog a read and be sure to check out the interactive demonstration web pages he's put up to help us grasp the genius of the Apollo engineering teams. [Ken]'s been featured on Hackaday a number of times reverse engineering such diverse things as a Yamaha DX7 Synth chip.
#radiohacks #space #apollo #jpl #kenshirriff #nasa #radar #rangefinder
[Ken Shirriff] Takes a Bite of the Apple-I
The Apple-I was a far cry from Apple's later products. A $666 single-board computer, the product had some unique design features including using a shift register for video memory to save money. The shift registers of the day required high-current clock pulses that ranged from -11 to 5V and there was a DS0025 clock driver chip to handle the job. [Ken Shirriff] takes the unusual chip apart for us in a recent blog post.
The use of a shift register as memory isn't a new idea. Really old computers like EDSAC used mercury delay lines as memory which was essentially a physical shift register. In those cases, the ALU and other processing only had to deal with a bit at a time, further simplifying things. For the Apple, there were seven shift registers to store 6-bits of display data and a cursor position. The 6 bits of character data drove -- indirectly -- a character generator ROM to convert the data into dots for the display.
Driving all those shift register flip flops requires a lot of clock current, so the DS0025 uses an unusual transistor design. There are 24 separate emitters in two groups. It acts like a large transistor, but you could also consider it as two 12-emitter transistors or 24 separate transistors in parallel. The metal wiring, interestingly enough, tapers because at the start of the conductor, the current for all 12 sub-transistors flows, but by the end, it is only the current for the last sub-transistor, so the conductor doesn't have to be as wide. In addition, the two transistors have to have matched resistance which requires careful design so the transistors turn on at the same time.
The final result is an inverter that can provide 1.5 amps. This current helps overcome the relatively large capacitance in the shift register's clock line. The clock rate was 1 MHz and the load capacitance was about 150 picofarads.
We enjoy [Ken's] posts ranging from mysteries to space hardware. It is always interesting to see what is inside these devices or, at least, what was in the old devices we've all seen.
#retrocomputing #reverseengineering #apple1 #icdecapsulation #kenshirriff #shiftregister
A Particularly Festive Chip Decapping
As we approach the moment in the year at which websites enter a festive silly season of scrambling to find any story with a festive angle, we're pleased to see the ever-reliable [Ken Shirriff] has brought his own take on Christmas tech to the table with a decapping of the UM66T melody chip that has graced so many musical greeting cards.
The surprise in this age of ubiquitous microcontrollers is that this is not a smart device; instead it's a single-purpose logic chip whose purpose is to step through a small ROM containing note values and durations, driving a frequency generator to produce the notes themselves. The frequency generator isn't the divider chain from the RC oscillator that we might expect, instead it's a shift register arrangement which saves on the transistor count.
Although the UM66 is a three-pin device, there are a few other pins on the die. These are likely to be for testing. As a 30+ year old product its design may be outdated in 2021, but it's one of those chips that has survived without being superseded because it does its task without the need for improvement. So when you open a card and hear the tinny tones of a piezo speaker this holiday season, spare a thought for the ingenuity of the design behind the chip that makes it all possible.
#holidayhacks #parts #chipdecap #christmas #kenshirriff #um66t
