DB25 #6 — laplink

The earliest IBM PC laptops mirrored the development of the PC itself, though often with less expandability. IBM’s first PC laptop was the IBM PC Convertible, launched in 1986, just a year before the launch of the new wave of IBM PS/2 machines that would seek to redefine the PC on terms more favorable to IBM.

The PC Convertible hewed pretty close to the original PC, remarkable for a machine introduced five years later. Floppy drives (though compact 3.5” drives replaced the PC 5.25” drives), CGA graphics, Intel 8088 processor running at 4.77MHz.

On the desktop side of the business, IBM had already moved on to the PC/AT — hard drives, high density floppy drives, 286 processors and extended color graphics. Then, as now, there were practical reasons that the most powerful desktop systems simply couldn’t be realized as battery-powered laptops. As a practical matter, this meant that laptops were often positioned as companion systems.

Laptops soon leveled up. A few months after the introduction of the PC Convertible, Toshiba released the T1200 as a follow-up to their initial laptop offering. Clock speed was double that of the original PC but the biggest deal was a compact 3.5” hard drive that offered the same 20 MB common in desktop systems.

Finally, a battery-powered portable with enough capacity for the records of an entire business and small enough to forget in the overhead compartment of the Eastern Shuttle from DC to New York. How do you back that thing up, anyway?

Floppy disks were a cumbersome option. There was no tape drive nor a port to which one could be attached. The built-in modem, if you had one, was barely a better option at 1200 baud. There was no built-in Ethernet port — the twisted pair Ethernet standard 10BaseT wasn’t even adopted until 1990. Contemporary Apple machines (both Mac and Apple IIgs) offered Apple’s high-speed serial LocalTalk network which could directly connect two machines with an inexpensive cable. The LocalTalk port itself was introduced as a way to share large desktop publishing documents with Apple’s new LaserWriter laser printer, and to share access to the expensive printer in the kind of small creative media agencies hinted at in shows like “Who’s the Boss?” (I think the home-office-based creative universes of Charles in Charge and Designing Women were both probably PC-based).

Was there somehow a way that a humble PC laptop, too, could use its DB25 printer port to share files? Yes. Not only that, Traveling Software had been selling LapLink and a matching DB-25 to DB-25 ‘null modem’ cable since 1983 for just this purpose. This predates the 1984 introduction of the Macintosh, the famous ‘1984’ Chiat/Day Super Bowl ad for the Mac, and even “Who’s the Boss”. Who was the boss indeed?

LapLink declined in the market as Ethernet rose. Oddly, one of the things that created the opening for it in the first place was the especially poor performance of the serial port controller chip in the original IBM PC and clones. That chip, the National Semiconductor 8250, had a FIFO buffer of only 1 byte. The subsequent PS/2 machines from IBM replaced the 8250 with the 16550 and its 16-byte buffer.

Then, the LapLink cable rose again. Early versions of Linux operating systems were shared principally over the Internet but they were installed mostly from floppy disks. See, early versions of the Linux kernel had no Ethernet support at all and it would be years before you could reasonably expect a given distribution of Linux to support whatever network card you happened to have. In this environment, everthing that was unlovable about floppy disks and parallel ports became an advantage. The original PC peripherals and ports didn’t really require third party drivers. That’s what the BIOS was. Better than that, the peripherals themselves were mostly built from off-the-shelf chips that had well-defined register programming interfaces. No matter what type of hard drive controller or network card you might have, you could boot Linux from a floppy disk using routines in the BIOS. The same became true for networking through the parallel port. Years after LapLink over the parallel port had been outclassed by other technologies, Linux re-popularized the cable for PLIP — essentially IP encapsulated over the original LapLink cable. With this, one machine could provide Linux installation services to another more quickly than with floppy disks. From there a full Linux distribution might have support for more sophisticated peripherals but the initial floppy disk bootstrapping the installation needed to support only the very simple programming model of the parallel port.

I used this method myself on several subnotebooks (like the Sony Vaio 505) as late as 1999. While the parallel port would survive for years (or decades) longer, one of the final nails in PLIP was broader support for IDE CD readers and writers. Another was the development of the Intel PXE standard. PXE finally provided something like a device-independent BIOS for networking. PXE was stable enough to support reliably loading Linux boot images over the network. New technologies in the Linux kernel, like initial ramdisks (initrd) and loadable kernel modules, made it pratical to load images of modest size over PXE and pivot directly during the installation process to native device drivers.

Fat lot of good any of this did for Who’s the Boss. That series wrapped up in 1992. Maybe 2025 will finally be the year of Linux on the fictional TV desktop. Unless, oh no, unless it was Silo. If we’re going to be recycling the same computers for the next three hundred years or so as result of nuclear apocalypse and/or tariffs, maybe keep any DB-25 LapLink cables you have lying around. We may need them.

This post pairs well with Aretha Franklin’s 1962 cover of “Respect” — intro music for 1988’s Murphy Brown. I‘ll bet Murphy used a TRS-80 Model 100 and filed stories over the built-in modem. Upload your work to the newsroom and let libraries back it up for you.