Old Laptops, Modems, And The Hackaday Retro Edition

We haven’t been getting very many submissions of extremely old computers loading up the Hackaday Retro Edition in a while. For shame. Thankfully, [alnwlsn] is here to pick up the slack from the rest of you with his latest accomplishment, getting two old laptops on the Internet with some old telecom equipment.

The first is a Toshiba from about 1995, Pentium processor, 12 MB of RAM, and a 10 GB (!) hard drive. [aln] had a PCMICA modem sitting around, and with Windows 95 and IE 5.5, he was able to slowly connect.

Pentium class machines are okay, but the next one – a Zenith Data Systems laptop from about 1987 – is awesome. 80C88 CPU, two 720k floppy drives, and the exact amount of RAM in that quote falsely attributed to [Bill Gates]. [alnwlsn] is connecting with a 28.8k modem, but the serial port only supports up to 9600. It’s a computer so old, even the retro edition’s main page times out. The about page, though, loaded fine.

[alnwlsn] used a modem with both of these laptops, but he doesn’t have dial-up or even a landline. This forced him to make his own line simulator that requires plugging in the phone line at the right time, manually ringing a modem connected to another computer, and letting PPP take it from there. It’s a crude circuit, but it works. slow, but it works. Video below.

10 thoughts on “Old Laptops, Modems, And The Hackaday Retro Edition

    1. I use to run Doom2 over two computers without LAN over a decade ago by using ATA (answer) on one machine and ATD (Dial, but without a number) on the other first with a phone cable plugged directly between the two modems.

      Just tell the program it’s a normal Serial connection with a speed of whatever the models connected to, and you should be good to go.

  1. If you have a landline and need/want some numbers to call just search for the Telecomix dial-in numbers. Or just use this number in Madrid, Spain: +34 912910230 user:hackaday@trovator.com pass:hackaday
    Those are modems with free internet access (but you have to pay the call!)

    You may use an ATA+voip provider, as many of them offer free calls to Europe landlines. And yes, you can connect to the Internet via dial-up using a voip line. But you have to set the bitrate to something like 2400 and use high quality codecs like μ-law or A-law.

  2. You can connect two modems together directly without a real phone line. I’ve done that many many years ago with a 2400baud and an 9600baud. You just have to use an ATA and an ATD command and let the modems fight for their rights! This setup was used for testing a little C XModem terminal program for a school project. My PC were two far from each other to use a serial cable.

    1. Depends, early serial chips had no buffers for input or output. This means every received byte triggered an interrupt that needed servicing right then. If the interrupt didn’t take in the data byte and clear the serial chip for the next one, data could get lost. Depending on whether RTS / CTS did their job.

      So the limit is really how fast your CPU can cope with having interrupts fired at it, push the relevant registers to the stack, do the I/O and memory access, etc. The 4.77 / 8MHz 8088 chips took lots of cycles per instruction, you don’t get a lot of MIPS out of them. In fact you’d be lucky for an actual whole MIP.

      The 16550 chip became popular in the mid-1990s with the Internet and 28.8k modems. It had a 16-byte buffer, you could set it to interrupt on every 4th, 8th, 16th byte in, and read the lot of them at once, ie 16x less interrupts and time serving interrupts. Obviously with the appropriate driver, otherwise they just acted like the old 8250. Typically they’d run with the trigger set at 8 bytes rather than the full 16. Maybe to save the odd chance of a byte falling off the end, if a 17th came in when it was full, using 8 would give you another 8 bytes worth of time for your interrupt service routine, even if it was called more often.

      Like quite a few people back then, my 16550 came as the actual chip, on an ISA card, with not much else. With that, the modem, and a serial cable, came to about 200 British quid all in. Still it got me a few years of glorious Internet, before I bought it’s 56k replacement for less than a tenner.

  3. Why not just use a null modem cable connecting the 8088’s serial port and a USB-serial converter on a modern machine that also runs PPP server and routes traffic onto the internet? If the CPU and UART chip can keep up this could achieve 115200 bits per second, faster than any dialup connection ever did!

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