@gloriouscow.bsky.social
Developer of MartyPC - a cycle-accurate IBM PC/XT Emulator
https://github.com/dbalsom/martypc
and fluxfox - a PC floppy disk image library
https://github.com/dbalsom/fluxfox
Retro enthusiast and shameless computer geek
https://github.com/dbalsom/martypc
and fluxfox - a PC floppy disk image library
https://github.com/dbalsom/fluxfox
Retro enthusiast and shameless computer geek
what do all these bodges do?
they appear to address a conflict that would occur during DMA bus cycles when you had a certain peripheral installed that would do DMA transfers from the upper half of memory (the logic is gated on address line A19)
they appear to address a conflict that would occur during DMA bus cycles when you had a certain peripheral installed that would do DMA transfers from the upper half of memory (the logic is gated on address line A19)
November 27, 2025 at 11:43 PM
what do all these bodges do?
they appear to address a conflict that would occur during DMA bus cycles when you had a certain peripheral installed that would do DMA transfers from the upper half of memory (the logic is gated on address line A19)
they appear to address a conflict that would occur during DMA bus cycles when you had a certain peripheral installed that would do DMA transfers from the upper half of memory (the logic is gated on address line A19)
That means when IBM realized they had a fix to make, they had to do this:
November 27, 2025 at 11:35 PM
That means when IBM realized they had a fix to make, they had to do this:
On the original 5150 motherboards, U101 was just a spare IC spot. No traces ran to it.
November 27, 2025 at 11:35 PM
On the original 5150 motherboards, U101 was just a spare IC spot. No traces ran to it.
U100 is just a spare IC spot. No traces to connect to it. IBM just anticipated they might need to throw in some extra logic as a fix, so this was a way a chip could be added and then bodge-wired however was needed.
IBM loved their bodge wires. They were usually yellow.
IBM loved their bodge wires. They were usually yellow.
November 27, 2025 at 11:27 PM
U100 is just a spare IC spot. No traces to connect to it. IBM just anticipated they might need to throw in some extra logic as a fix, so this was a way a chip could be added and then bodge-wired however was needed.
IBM loved their bodge wires. They were usually yellow.
IBM loved their bodge wires. They were usually yellow.
ain't no party like a DRAM party cuz a DRAM party don't stop
November 27, 2025 at 10:13 PM
ain't no party like a DRAM party cuz a DRAM party don't stop
The 8088 had a multiplexed bus. That means that the first 8 address lines are also the data lines! The address for a bus cycle was only valid on the first cycle, T1. The 8288 bus controller produced an Address Latch Enable (ALE) signal that caused these three latch chips to store the address.
November 27, 2025 at 10:04 PM
The 8088 had a multiplexed bus. That means that the first 8 address lines are also the data lines! The address for a bus cycle was only valid on the first cycle, T1. The 8288 bus controller produced an Address Latch Enable (ALE) signal that caused these three latch chips to store the address.
We can do some cool stuff with this
here's a visualization of how the CPU address lines flow out to the address latches
#retrocomputing
here's a visualization of how the CPU address lines flow out to the address latches
#retrocomputing
November 27, 2025 at 10:01 PM
We can do some cool stuff with this
here's a visualization of how the CPU address lines flow out to the address latches
#retrocomputing
here's a visualization of how the CPU address lines flow out to the address latches
#retrocomputing
I knew someone would ask! U101 is not always present. It is a 74LS32. According to some service notes, it corrects some compatibility issues when using AMD DMA controllers. I don't know how to express that with a short tag!
U1 is an amplifier for the cassette interface.
U1 is an amplifier for the cassette interface.
November 27, 2025 at 8:36 PM
I knew someone would ask! U101 is not always present. It is a 74LS32. According to some service notes, it corrects some compatibility issues when using AMD DMA controllers. I don't know how to express that with a short tag!
U1 is an amplifier for the cassette interface.
U1 is an amplifier for the cassette interface.
Even by the late 80s they were combining a lot of this logic into LSI chipsets.
November 27, 2025 at 8:20 PM
Even by the late 80s they were combining a lot of this logic into LSI chipsets.
:) I wanted to put the chips function on rather than just say "74LS08," but it's used for four different unrelated purposes, so MISC AND GATES it is.
November 27, 2025 at 8:13 PM
:) I wanted to put the chips function on rather than just say "74LS08," but it's used for four different unrelated purposes, so MISC AND GATES it is.
The MCU in a disposable vape probably has 10x the transistor count of every single thing on this board
November 27, 2025 at 8:11 PM
The MCU in a disposable vape probably has 10x the transistor count of every single thing on this board
Isn't it just because it's telling you your computer is slow and turtles are slow?
November 27, 2025 at 7:50 PM
Isn't it just because it's telling you your computer is slow and turtles are slow?
You can do some extremely cool stuff with it. For example using Rust's wgpu crate, I can write a single application that renders in 3D and compile it natively or for wasm and it will run in the browser.
I am absolutely certain some assholes will abuse it. Just more reasons to use adblock
I am absolutely certain some assholes will abuse it. Just more reasons to use adblock
November 27, 2025 at 1:34 AM
You can do some extremely cool stuff with it. For example using Rust's wgpu crate, I can write a single application that renders in 3D and compile it natively or for wasm and it will run in the browser.
I am absolutely certain some assholes will abuse it. Just more reasons to use adblock
I am absolutely certain some assholes will abuse it. Just more reasons to use adblock
my aftermarket dashcam came with a cutoff switch if it detects the battery voltage dropping too low. when i saw that i was like - why aren't all the accessory circuits tied into something like that?
November 25, 2025 at 4:36 AM
my aftermarket dashcam came with a cutoff switch if it detects the battery voltage dropping too low. when i saw that i was like - why aren't all the accessory circuits tied into something like that?
okay I found the poster in question and my God these people are arguing they were called "hard disks".
no. I don't care if you called 3.5" disks flipperschnitzels but there is no reality in which anyone called them hard disks.
no. I don't care if you called 3.5" disks flipperschnitzels but there is no reality in which anyone called them hard disks.
November 24, 2025 at 5:26 AM
okay I found the poster in question and my God these people are arguing they were called "hard disks".
no. I don't care if you called 3.5" disks flipperschnitzels but there is no reality in which anyone called them hard disks.
no. I don't care if you called 3.5" disks flipperschnitzels but there is no reality in which anyone called them hard disks.
this is me devolving back into goo to escape modern life
November 24, 2025 at 5:12 AM
this is me devolving back into goo to escape modern life
Which led me to this video on a detailed 3d recreation of the original
www.youtube.com/watch?v=KomY...
www.youtube.com/watch?v=KomY...
The FIRST Japanese Typewriter - Invented by Kyota Sugimoto 1915 日本の最初のタイプライター 杉本京太によって発明されました
YouTube video by Michael's music instruments
www.youtube.com
November 24, 2025 at 5:10 AM
Which led me to this video on a detailed 3d recreation of the original
www.youtube.com/watch?v=KomY...
www.youtube.com/watch?v=KomY...
The basic concept was patented in 1917!
November 24, 2025 at 5:10 AM
The basic concept was patented in 1917!
you sent me down a rabbit hole on this one.
apparently the way this thing works is the lever arm is like a two-axis pointer, but it corresponds directly to a tray of lettersets. The lever action plucks the selected character out of the tray and plonks it up onto the roller and somehow puts it back
apparently the way this thing works is the lever arm is like a two-axis pointer, but it corresponds directly to a tray of lettersets. The lever action plucks the selected character out of the tray and plonks it up onto the roller and somehow puts it back
November 24, 2025 at 5:03 AM
you sent me down a rabbit hole on this one.
apparently the way this thing works is the lever arm is like a two-axis pointer, but it corresponds directly to a tray of lettersets. The lever action plucks the selected character out of the tray and plonks it up onto the roller and somehow puts it back
apparently the way this thing works is the lever arm is like a two-axis pointer, but it corresponds directly to a tray of lettersets. The lever action plucks the selected character out of the tray and plonks it up onto the roller and somehow puts it back
imagine my disappointment when the new-old-stock box of floppies i got came with labels that don't stick anymore :(
November 24, 2025 at 4:53 AM
imagine my disappointment when the new-old-stock box of floppies i got came with labels that don't stick anymore :(
my favorite detail about the whole affair is that at the peak of people's frustration with their drives just dying out of the blue and going "click-click-click" is that IoMega, the company that made the Zip disk, came out with a new product during all this and called it...
Clik. I shit you not.
Clik. I shit you not.
November 24, 2025 at 4:26 AM
my favorite detail about the whole affair is that at the peak of people's frustration with their drives just dying out of the blue and going "click-click-click" is that IoMega, the company that made the Zip disk, came out with a new product during all this and called it...
Clik. I shit you not.
Clik. I shit you not.