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Expanded vs Extended memory, or EMS vs XMS

Dave Farquhar Retro Computing August 11, 2017October 5, 2019Bill Gates, intel, memory slots, XT

DOS veterans may remember messing with expanded and extended memory to get memory above 640K. Here’s what you need to know about expanded vs extended memory, or EMS vs XMS. They are two different approaches to solving the same problem.

Dave Farquhar

David Farquhar is a computer security professional, entrepreneur, and author. He has written professionally about computers since 1991, so he was writing about retro computers when they were still new. He has been working in IT professionally since 1994 and has specialized in vulnerability management since 2013. He holds Security+ and CISSP certifications. Today he blogs five times a week, mostly about retro computers and retro gaming covering the time period from 1975 to 2000.

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Why did old PCs have a turbo button?

Dave Farquhar Retro Computing August 1, 2017March 25, 20241980s, 1990s, benchmark, compaq, IBM, XT

Old PCs, especially PCs from the 1980s to the mid 1990s, have a button with the curious label “Turbo.” On some PCs, a number on the front changes when you push it, or an LED toggles on or off. Why did old PCs have a turbo button?

Turbo buttons are a quirk of old PCs, kind of like their beige color that tends to turn yellow, but it served a functional purpose.

Dave Farquhar

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Why did IBM fail at PCs?

Dave Farquhar Retro Computing July 3, 2017October 4, 20211980s, 1990s, acer, AIX, apple, compaq, datacenter, dell, hp, IBM, intel, lenovo, mainframe, Packard Bell, Personal Computer, proprietary unix, thinkpad, unix, VHS, XT

If you ask why did IBM fail, I assume you mean why did IBM ultimately fail in the personal computer market. IBM is still in business, after all. But its exit from the PC market after 24 years, including a period of dominance in the 1980s, does seem curious. And it raises another question: What does IBM do now?

I experienced IBM’s fall in this market firsthand. I sold computers at retail in 1994 and 1995. IBM’s computers at that time were no worse than anyone else’s, but I had an extremely difficult time selling them. Many consumers didn’t trust IBM and didn’t want to get somehow locked in. There was nothing wrong with those machines, but it sure was a lot easier to just sell them a Compaq.

Dave Farquhar

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IBM PS/2 vs PC

Dave Farquhar Retro Computing June 9, 2017May 7, 20241980s, 1990s, apple, apple ii, asus, compaq, IBM, intel, VGA, x86, XT

The IBM PS/2 line was a fairly radical departure from the older IBM PC line. This was deliberate, as IBM wanted to disrupt the clone industry, which it saw as a threat to its business. Here’s a look back at the IBM PS/2 vs PC, the line it replaced.

IBM succeeded with the PC because it created an ecosystem, not just a PC. IBM’s misstep was creating an open architecture and then trying to close it back up after the fact with the PS/2. In IBM’s defense, it’s not clear whether they knew this at the time. If nothing else, in the case of the IBM PS/2 vs PC, IBM created a classic case study of open architecture vs closed.

Dave Farquhar

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Commodore 64 vs Amiga

Dave Farquhar Retro Computing March 3, 2017September 6, 20181980s, 1990s, 6502, amiga, amiga os, atari, atari st, commodore, commodore 64, compaq, hp, intel, kmart, motorola, Packard Bell, Personal Computer, unix, XT

Looking at the Commodore 64 vs Amiga seems a little odd, at least to me. After all, the machines were never intended to be rivals. The Amiga was supposed to succeed the 64. Commodore bought Amiga because they couldn’t make a 64 successor on their own, so they intended for the Amiga to replace it. It didn’t fully succeed, and maybe that’s why the comparison is still interesting.

Looking back, the machines may seem similar today. But in 1985 they sure didn’t.

Dave Farquhar

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Building DOS gaming PCs

Dave Farquhar DOS, Retro Computing August 10, 2015May 1, 20251980s, 1990s, amiga, atari, atari st, compaq, IBM, intel, macintosh, micron, Packard Bell, Tandy, tandy 1000, VGA, XT

The ultimate DOS gaming PC is a topic that I’ve seen come up in forums frequently, and that I’ve been asked directly a number of times. I guess since I published advice on running DOS games on Windows PCs on two continents, people figured I knew something about that. I guess I fooled them!

The trouble is that no single PC can really be the “ultimate” DOS game machine. Well, not if your goal is to be able to optimally run everything from early 1980s titles designed for the original IBM PC up to the last DOS version of Quake. I learned that the hard way in 1995 or 1996, even before Quake existed. Read more

Dave Farquhar

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The Post-Dispatch may be giving the wrong idea about the dollar value of vintage computers

Dave Farquhar Retro Computing February 6, 2014September 15, 20251541, 1980s, 1990s, amiga, apple, apple ii, Apple Lisa, collectibles, commodore, commodore 64, Commodore Amiga, compaq, dell, hp, IBM, macintosh, radio shack, recycling, VGA, XT

Disclaimer: I wrote this article back in 2014. I leave it here as a snapshot of the state of how things were in 2014. The situation at the time you are reading this is likely different.

Articles like Top 10 collectibles for value, from the Post-Dispatch this week, frequently make me nervous, mostly because of statements like this one:

[D]id you know that computer parts can bring home cash, too?

Statements like that tend to get people’s hopes up way too high. I find the timing interesting though, seeing as a TRS-80 Model 1 sold at a St. Louis estate sale this past weekend. The estate seller’s reaction? “Normally you can’t give that stuff away.”

Dave Farquhar

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IBM PCjr and Tandy 1000

Dave Farquhar Retro Computing January 29, 2014September 26, 20221980s, apple, apple ii, christmas, commodore, commodore 64, IBM, ibm pcjr, lenovo, macintosh, mainframe, Personal Computer, radio shack, Tandy, tandy 1000, XT

On January 29, 1984, two computers hit the market. One was Apple’s Macintosh. It needs no introduction. The other was the IBM PCjr. It was a little less successful. We’ll talk about what this has to do with the Tandy 1000 in a minute.

The PCjr is one of the biggest flops in computing history. Few people know much more about it than that. It ended up being an important computer, but it certainly didn’t meet IBM’s expectations. Read more

Dave Farquhar

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How we learn

Dave Farquhar Uncategorized July 29, 2013July 28, 2013IBM, insulin, Lawn mower, lifehacker, XT

An article on Lifehacker this week explained a lot about how I initially became a computer professional. Its advice was to fly by the seat of your pants, try things without guidance or manuals, not be afraid to fail occasionally, and learn before you go to sleep.

So when I spent many nights in my late teens disassembling and reassembling obsolete IBM PC/XT clones to learn how they worked, I was unwittingly doing all of it right.

Dave Farquhar

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The $99 Android tablet of 2013: The Hisense Sero 7 LT (or Lite)

Dave Farquhar Android June 13, 2013November 3, 2025android, Ars Technica, black friday, IBM, Jelly Bean, nexus, XT

So when I decided to bring myself into the current decade, tablet-wise, I opted for the $150 Hisense Sero 7 Pro, though I was certainly curious about its $99 little brother. Unfortunately, information on the Sero 7 Lite hasn’t been as easy to come by–people are understandably excited about getting a Nexus 7 clone for $50 less that actually includes two desirable features that the real thing lacks. This must be what it felt like to be in the market for an IBM PC/XT when the Leading Edge Model D came out in the summer of 1985. Read more

Dave Farquhar

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