I’ve seen a couple of Commodore-related search queries hit lately, so I’m going to take a stroll down memory lane with two questions:
Can you connect two computers to one single 1541 or 1571 disk drive?
And what was the fastest Commodore modem?
Let’s take the disk drive question first. Without additional equipment, you can’t do it. The Commodore serial bus can’t handle having two computers on it. Way back in the early 1980s when disk drives cost $300, there were some devices that let you share a floppy among multiple computers. The grade school I attended had one such device, which I remember was called a VIC Switch. I don’t know who made it. But if there was one thing worse than waiting three minutes for a program to load, it was waiting in line to wait your three minutes for a program to load.
Now that the street value of a working Commodore 1541 is around 10 bucks, it’s best to just dedicate one or more drives to each computer. If you could manage to find a VIC Switch today, chances are you’d pay more than the cost of the drive for it.
As for modems, there are several ways to take that question. The fastest modem Commodore produced was the 1670, which ran at 1200 bps and worked with a 64, 128, or VIC-20. They also produced a modem called the 1680 for the Amiga, which also ran at 1200 bps.
A third party called Aprotek produced a 2400 bps modem that plugged straight into the Commodore user port. I owned one for a while. It was cheaply made but worked well enough and didn’t require any extra hardware to connect it.
Two terminal programs that appeared late in life, Desterm 128 (by Matt Desmond) and Novaterm 64 (by Nick Rossi), had special routines that allowed the 64 to operate at up to 4800 bps and the 128 to reach 9600 bps, as long as you had an RS-232 adapter and an appropriate modem. The author of Desterm, as I recall, specifically recommended US Robotics modems. Commodore computers didn’t have a dedicated UART chip, relying on software to keep costs down. So that limited the machines’ telecommunications abilities.
A few companies marketed RS-232 adapters that contained a 6551 UART (or ACIA) chip in them. With those, and with software coded to use them, a Commodore could theoretically reach 38.4 kbps. I never owned one of those cartridges, so I never tried a Commodore out with a 56K modem to see what speed it could reach.
And I suppose that leads to another question: Why did Commodore leave out that chip that would have allowed the 64 and 128 to reach higher speeds? The main reason was because the 64 was specifically designed to reach a price point of $595 and drop to $299 as quickly as possible. In 1982, nobody else could make a 64K computer and sell it for under $600. Adding that chip would have added perhaps another $30 to the cost of the computer, but few people would have used it. In 1982, a 1200 bps Hayes Smartmodem cost $699, and Commodore was able to make the 64 keep pace with that through software. It wasn’t until 1985 that 2400 bps modems hit the market, and Commodore initially expected the 64 to have a shelf life of about two years.
Arguably, adding the 6551 UART chip to the 128 would have made more sense, but then again, the 128, released in 1985, was designed to hit a price point of $349 and it, too, was designed with a short life expectancy in mind. And Commodore didn’t expect many buyers of the 128 to run out and spend $549 on a Hayes 2400 bps modem to connect to their $349 computer.
In the meantime, a number of programmers found ways to get the 64 and 128 to keep pace with a 2400 bps modem entirely through software, and by the late 1980s the programmers of Matt Desmond and Nick Rossi hit higher speeds still.
How and why I remember this stuff after all these years is yet another question.