More Fun with ISA DMA

Posted on January 13, 2020 by Michal Necasek

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 DMA transfers; that proved to be unfounded, at least in the UMBPCI case, but what the utility does is nevertheless quite interesting.

Dual NEC D8237AC-% DMA controllers in a PC/AT clone board.
Classic cascaded 8237A DMA controller chips in a PC/AT clone

First some background about what DMACHK does and why it exists in the first place. UMBs are generally prone to causing difficulty with DMA, and UMBPCI is no exception. The way UMBPCI works is that it enables memory between 640KB to 1MB for use with UMBs. Such memory is normally only intended for ROM shadowing and in some chipsets, it is not accessible via DMA (whereas EMM386/QEMM/386MAX use paging to remap normal memory into the UMB range, causing physical addresses to differ from linear ones).

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Posted in PC architecture, PC hardware, Software Hacks | 8 Comments

MS OS/2 SDK Document Dump

Posted on January 3, 2020 by Michal Necasek

The Microsoft OS/2 1.0 SDK library section got a big fat update. Over the holidays I managed to finalize and upload about 25 PDFs, some of which have been lying on my NAS in 98% completed state for almost 10 years, and some of which have been only scanned a few months ago. I may still have one or two ring binders lying around and those will be added when I find them and scan them.

It’s thousands of pages of Microsoft documentation from 1987 and early 1988. Some of the documents ought to be interesting for DOS programmers since they include retail MASM 5.0 and MS C 5.0 documentation. There are also pre-release versions of the MS C/MASM 5.0 documentation from May 1987. There are separate “diff” addenda documenting the OS/2 specific features of the tools pertaining to the beta compilers shipped with the MS OS/2 SDK. And there is actual pre-release OS/2 programming documentation from April 1987, right after OS/2 was publicly announced.

Posted in Documentation, Microsoft, OS/2 | Leave a comment

The Cape Cod Disaster

Posted on December 16, 2019 by Michal Necasek

Here’s a motherboard Intel very quickly wanted to forget about:

Intel Desktop Board CC820 with CPU and SDRAM, early 2000
Intel CC820 Desktop Board (early 2000)

It’s the Intel CC820—or Cape Cod—desktop board, a product that was late to market (not unusual) and within a few months, the subject of a recall (quite unusual). As the CC820 designation suggests, the board was built on the ill-fated Intel 820 ‘Camino’ chipset.

The Camino chipset was supposed to be released roughly in mid-1999 as a replacement of the workhorse 440BX chipset for mainstream desktops. At the same time, Intel changed how it segmented the market. The 440BX supported up to two processors, while the 820 didn’t (though the 820DP variant did); the 820 chipset was targeted for typical desktops, while the Intel 840 chipset was meant for high-end workstations with two processors. Note that the Intel 810 chipset was meant for “value” PCs, and played that role quite successfully.

The 440BX chipset was limited to 100 MHz FSB; the 820 supported 100 and 133 MHz FSB for the then-new Coppermine Pentium III processors. The 440BX chipset was limited to ATA-33, while the 820 supported ATA-66. The 440BX only supported AGP 2x, while the 820 provided AGP 4x capability.

But that wasn’t all. The 820 chipset also supported RDRAM, or Rambus DRAM. And therein lay the problem.

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Posted in Bugs, Intel, PC hardware, PC history, Pentium III, RDRAM | 45 Comments

DOS Wireless Networking, Continued

Posted on December 11, 2019 by Michal Necasek

As I recently mentioned, wireless networking is extra difficult when the access point reboots itself at the slightest hint of heavier traffic. The faulty TP-Link router was temporarily replaced with a Netgear WG602 of similar vintage. The Netgear has been solid and has no trouble transferring tens of megabytes without a glitch.

I should note that although the TP-Link turned out to be bad, it has nicer diagnostics than the Netgear and it is slightly more tweakable. But a working AP wins out any day.

Agere ORiNOCO wireless PC Card in an IBM ThinkPad 760XL
Agere ORiNOCO wireless PC Card in a ThinkPad 760XL

The next project was getting IBM’s TCP/IP 2.1 working wirelessly. The protocol stack is almost completely dynamically loadable and unloadable, and comes with a decent NFS client. I had previously got IBM TCP/IP going in a DOS VM without much difficulty, but convincing it to work with a Cisco Aironet 350 turned out to be surprisingly tricky.

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Posted in DOS, Networking, NFS, TCP/IP, Wireless | 3 Comments

The Danger of Datasheets

Posted on December 11, 2019 by Michal Necasek

A few days age I came across an article about the 8237 DMA controller in an old German computing magazine (DOS Extra, issue 1 ’87/88, page 123, Schnelle Speicherverwaltung mit dem DMA-Controller, or Fast memory management with the DMA controller). While skimming through the article, I began to suspect that the although the author did a good job reading the 8237 datasheet, he had only a rather vague idea of how the controller was actually wired up in the IBM PC.

On closer reading of the article, my suspicion was confirmed. While there is some PC-centric information in the article (which I/O ports the 8237 is mapped at, or the fact that the DMA controller is used for memory refresh in the IBM PC), absolutely crucial IBM-specific information is missing.

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Posted in Corrections, PC hardware, PC press | 29 Comments

Power Trouble

Posted on December 5, 2019 by Michal Necasek

This will not come as a surprise to anyone who is deeply familiar with PC hardware; the other 99% please bear with me.

A good quality and compatible power supply is crucial to the healthy operation of a PC. The catch is that whether a PSU (Power Supply Unit) is actually compatible and truly good quality may not be very apparent. Even worse, when there are problems, the symptoms may be extremely non-obvious and tend toward “analog” failures—sometimes things work, sometimes they don’t, seemingly with no rhyme or reason.

Probably my favorite retro mainboard is an Alaris Cougar, a VL-bus OEM board manufactured by IBM, also known as IBM Cobalt-AT. The board has an onboard 100 MHz IBM BL3 processor (a triple-clocked Blue Lightning 486DLC, i.e. IBM’s rocket-boosted 386), separate Socket 2 for a 5 Volt 486 SX/DX/DX2 or Pentium Overdrive, a blazingly fast Adaptec VLB IDE controller, and MR BIOS which POSTs about hundred times faster than conventional BIOS implementations (well, not really but it often feels that way, because it is easily 10 times faster).

The board is from 1993 or 1994 and of course it uses the Baby AT form factor, with a classic AT P8/P9 power connector (ever plugged those in backwards? I have…). AT power supplies are getting harder to find and their on/off switches are not suitable for bench operation. An ATX PSU with a switch on the back, combined with a simple ATX to AT adapter, does a better and usually quieter job. Except not always.

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Posted in PC hardware, PC history | 13 Comments

Wireless Networking in DOS

Posted on December 2, 2019 by Michal Necasek

Wireless networking has a long history, longer than most people realize. NCR’s WaveLAN was available in 1990 and of course supported DOS. But WaveLAN was only the precursor to IEEE 802.11 and it is completely incompatible with IEEE-standard networking equipment.

The IEEE 802.11b standard came out in 1999, specified a 11 Mbps signaling rate, and it’s about the oldest not totally obsolete wireless networking standard. The trouble is that IEEE 802.11b equipment appeared when DOS was almost gone from home and corporate PCs, although it still survived as a “pre-boot” environment for running Norton Ghost, Partition Magic, Drive Image, and similar products. The upshot is that until the early 2000s, there was demand for DOS networking drivers for then-current hardware.

My need was seemingly simple: I set up an old ThinkPad 760XL (166 MHz Pentium MMX) running DOS for my son to play 1990s games on, especially but not exclusively Sierra and LucasArts adventures; for that purpose, the laptop is quite suitable, it has a decent ESS sound chip and a CD-ROM. Moving data to the laptop on a CF card with a PCMCIA adapter is not difficult, but it gets old; it would be really handy to have the laptop on the network, accessing the home NAS via either SMB or NFS.

IBM ThinkPad 760XL with Cisco Aironet PCM350 WiFi PC Card.
Vintage Wireless, circa 2000

The laptop is of course old enough that it has no built-in Ethernet or WiFi, although it has two PCMCIA/CardBus (at least I believe they’re also functional as CardBus) slots. But the laptop is portable, and it’s in a corner of the house where there’s no Ethernet socket nearby. So WiFi would be really great. But is it even possible to get a DOS laptop on a WiFi network in 2019?

The short answer is “yes, but”. The long answer follows.

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Posted in DOS, Networking, Wireless | 20 Comments

More on NX Insanity

Posted on November 29, 2019 by Michal Necasek

This article was supposed to be published about two years ago but got forgotten and ignored until now. It’s not the only such article. Perhaps it will start a new “better published late than never” series.

After looking more closely into the nonsense surrounding the implementation and usage of the NX feature, I ended up with more questions than answers. And it’s definitely not the fault of AMD, the people who first defined and implemented NX.

A big contributor is Microsoft, too. The code to detect and enable NX in Windows 10 (analyzing the original 10240 build here) is, to put it mildly, weird. That is very much at odds with Server 2003 (WRK) which has completely straightforward code to detect and, if present and requested, enable NX.

First let’s consider 64-bit Windows 10 10240 because it’s simpler. Given that NX was introduced in and defined as a non-optional part of the AMD64 architecture, a 64-bit OS should be able to query bit 20 (NX) in CPUID leaf 80000001h, register EDX. But that’s not what Windows 10 does. Continue reading →

Posted in AMD, Bugs, Intel, Microsoft | 13 Comments

The Sad End of Intel Desktop Boards

Posted on November 11, 2019 by Michal Necasek

As previously discussed on this blog, Intel decided to quit the desktop board business in 2013. What has not been discussed is how Intel treated the buyers of the last generation (i.e. 8-series Lynx Point chipsets) of those boards. Since I have now acquired two of those boards, DZ87KLT-75K and DQ87PG, I had an opportunity to familiarize myself with the situation.

The DZ87KLT (Kinsley Thunderbolt) and DQ87PG (Spring Cave) were released in mid-2013 and were sold for about three years. They supported the then-new LGA1150 socket for Haswell CPUs.

In 2014, Intel released the updated and faster Haswell Refresh CPUs, as well as the Devil’s Canyon i7-4790K, Intel’s first 4.0 GHz processor (ten years after the Pentium 4 very nearly got there first). For most owners of existing LGA1150 boards, supporting the new processors was just a matter of updating the BIOS.

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Posted in Intel, PC hardware, Software Hacks | 15 Comments

The i860 Conspiracy

Posted on November 10, 2019 by Michal Necasek

I’ve been thinking of acquiring a board with the Intel 860 (Colusa) chipset. This chipset is historically interesting because it was Intel’s first chipset for NetBurst Xeons, and–at least according to Intel–the only chipset that supports the original Foster Xeon DP processors with the 180nm Willamette core.

The platform is interesting because it was Intel’s first dual-socket Pentium 4 implementation, and the i860 chipset was also the first with support for certain modern amenities like Message Signaled Interrupts (MSIs), enabled by the switch from a dedicated APIC bus to interrupt delivery via FSB messages.

The catch is that the i860 chipset was relatively short-lived, having been cursed with RDRAM. The i860 was introduced in May 2001, and in February 2002 it was already superseded by the DDR SDRAM-based E7500 (Plumas) chipset, which also coincided with the release of 130nm Prestonia Xeons based on the Northwood core.

The i860 was apparently so short-lived that Intel did not manage to release its own board based on the Colusa chipset. There were apparently only four board vendors who did: There was Supermicro P4DCE and P4DC6 (I am guessing that P4DC stands for Pentium 4 Dual Colusa); there was Tyan Thunder i860 (S2603); there was MSI 860D Pro; and there was an obscure Iwill DX400-SN.

The MSI and Iwill boards appear to be very hard to find. The Supermicro and Tyan boards are not, but there’s a catch.

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Posted in Intel, PC hardware, PC history | 15 Comments