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I've just released a little DOS program for checking if a machine's CPU is cycle-exact with an Intel 8088 or not. You can get it at https://www.reenigne.org/software/acid88.zip . It will likely crash on CPUs that don't implement undocumented instructions in a way that is functionally identical...

Using Ken Shirriff's beautiful die shots, I've reverse-engineered the format of the microcode ROM in the Intel 8088 and 8086 CPUs and disassembled it: https://www.reenigne.org/blog/8086-microcode-disassembled/ . Remarkably, I've uncovered some undocumented instructions which nobody seems to have...

I posted this thread on Vogons which might be of interest to some people here.

I have an IBM 5153 CGA monitor which I bought in the US and transported to the UK. I've been using it with a step-down transformer and it seems to work fine. However, I recently took a photo of it and sent it to another 5153 owner who told me that colour 8 was much darker on mine than on his...

Here's something I've been working on lately: GCC for 8088-80286. Now you can write C and C++ code for your IBM 5150 that uses the very latest C11 and C++14 standards! I've done a small amount of comparative testing and I think it generally generates better integer code than any other 8086...

I bought an Atari 520STFM from ebay, but unfortunately it was badly packed (bubble wrap and brown paper only, not even a cardboard box!) and when it arrived the case was smashed into a million pieces: Fortunately the seller quickly gave me a full refund. The machine itself seems to work (I'm...

As I mentioned in another thread, I was planning to put my XT online so that anybody who wants to can run programs on it. Well, I've done it - today I'm announcing the XT Server. It doesn't run DOS programs as is - there is an extremely minimal operating system I hand-coded in about 800 lines of...

I've got my XT set up so that I can remotely run programs on it from a laptop in a different room of my house, get results back over the serial connection and also remotely power-cycle it. One thing I've been thinking about doing with this setup is putting it online so that anybody who wants to...

I have two kids - Alex is 5 and loves playing Minecraft, Penelope is 3 and enjoys flash games like Starfall and Poisson Rouge. They're both very interested in what I'm doing when I'm tinkering with my XT, but what they really want is to play some games on it. However, they haven't been...

Continued from the 8088 prefetch algorithm thread (which was getting a bit off topic). Yes, exactly - this is for analyzing the execution of some specific pieces of code for a particular set of experiments, rather than being a general ISA bus analysis device - it's not as multi-purpose as...

I've spent a long time (probably way too long) staring at the schematics for the IBM CGA cards for one reason or another, and doing so has given me an idea for a sort of game. I'm not sure if there's anybody out there other than me who would be interested in playing it but if there is I'm sure...

I'm curious about what various 74xx/74Sxx/74LSxx logic ICs used to cost (in bulk) circa 1981. Specifically the ones used in the IBM CGA card which were 74LS00, 74LS02, 74S04, 74LS04, 74S08, 74LS08, 74LS10, 74LS32, 74LS51, 74S74, 74LS74, 74S86, 74LS86, 74S112, 74LS125, 74LS138, 74LS151, 74153...

Anybody know what the difference is between the various IBM CGA card part numbers? I know of four: 1501486, 1504910, 1501981 and 1501982. The one I have is a 1501486 and as far I can tell the circuit is the same one as in the XT Technical Reference Manual ibm_techref_v202_3.pdf available from...

I've heard before that the first revision of the XT system board was missing U90 but I never knew what that IC actually did. After it was mentioned in another thread I decided to try to figure out what it did. I found the updated schematic in the March 1986 technical reference, and the...

Hi! My real name is Andrew Jenner. I'm a compiler developer by day job but I've been interested in old PCs for a while, probably because our family computer was an Amstrad PC1512 right up until 1994. After some 7 years of swapping floppies, I was pushing the limits of that machine in many ways...

Has anyone here successfully modified an XT power supply to use the innards of an ATX power supply? My XT's power supply stopped working (no voltage on the output lines, although it does seem to work on the first power-up after discharging the high-voltage capacitors). I figure a more modern...

I'm writing a little Arduino program to simulate a PC/XT keyboard, so that I can have a PC or XT on my workbench as well as a modern PC and control the former with the latter (and so that I don't have to devote space to two keyboards). This program will have several modes. In one mode it'll just...