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Category Archives: PC architecture
Who Knew What When
When Microsoft released the unique early beta build of Multitasking DOS 4, I quickly found out that it does not run in VirtualBox: This was a bit of a surprise, because the more-or-less released versions of Multitasking DOS 4 from … Continue reading
Posted in 286, DOS, IBM, Microsoft, PC architecture, PC history, VirtualBox
29 Comments
This Code Smells of Desperation
A few weeks ago I had the questionable pleasure of diving into the math exception handler of WIN87EM.DLL, the Windows 3.1 math emulator and FPU support library. Actually WIN87EM.DLL appears to have been first shipped with Windows 3.0, and the … Continue reading
Posted in Bugs, Microsoft, PC architecture, x87
19 Comments
Failing to Fail
The other day I was going over various versions of the venerable DOS/16M DOS extender from Rational Systems (later Tenberry Software). The DOS/16M development kit comes with a utility called PMINFO.EXE which is meant to give the user some idea … Continue reading
Posted in Bugs, Intel, PC architecture, x87
11 Comments
First ROM Shadowing
The other day I was asked an interesting question: What was the first BIOS with support for ROM shadowing? In the 1990s, ROM shadowing was common, at first as a pure performance enhancement and later as a functional requirement; newer … Continue reading
Posted in C&T, Compaq, IBM, PC architecture, PC history
55 Comments
Xenix 2.2 vs. VGA
The other day I started wondering why certain old versions of 286 and 386 XENIX look a bit weird in emulation: The characters are cut off, because XENIX sets up an EGA text mode with 8×14 character matrix but uses … Continue reading
Posted in 286, 386, PC architecture, PC history, VGA, Xenix
14 Comments
Learn Something Old Every Day, Part IV: Ctrl+Scroll Lock is Ctrl+Break
The other day I tried running NSNIPES, a multiplayer networked game that came with old versions of NetWare. The game worked fine, but I couldn’t get out of it. Esc did nothing, any “usual” combinations like Alt+X, Alt+Q or similar … Continue reading
Posted in NetWare, PC architecture, PC history
3 Comments
8237A DMA Page Fun
The other day I was trying to fill a couple of gaps in my understanding of the Intel 8237A DMA controller documentation. I wrote a small testcase that performed a dummy transfer and modified the base address and count registers … Continue reading
Posted in Intel, PC architecture, PC history
5 Comments
386 Cache Coherency
I’ve been slowly chewing my way through U.S. Patent 5,724,549, titled Cache Coherency without Bus Arbitration Signals, initially filed by Cyrix Corporation in 1992 and published in 1998 (when it was utterly irrelevant, but such is the life of patents). … Continue reading
Posted in 386, Cyrix, PC architecture, PC history
17 Comments
A Brief Visit to Disk Geometry Hell
Several weeks ago I thought I’d install NetWare 3.12 in a virtual machine using the BusLogic SCSI controller emulation. While configuring a 1.5 GB virtual drive, I thought I should be safe and not run into any trouble with a … Continue reading
Posted in BusLogic, IBM, NetWare, PC architecture, Storage
32 Comments
More Fun with ISA DMA
A reader comment on a previous post on ISA DMA pointed out that UMBPCI (or rather the DMACHK utility distributed with it) does something unusual with regard to ISA DMA. There was a suspicion of somehow accomplishing the mythical memory-to-memory … Continue reading
Posted in PC architecture, PC hardware, Software Hacks
8 Comments