As I mentioned in the Wonderful Atari 800XL, we had upgraded our 1050 disk drives with a US Doubler chip. The purpose of this chip was to 1) bring it up from dual-density to true double density and 2) greatly increase the transfer speed.

The US Doubler was from ICD, a popular maker of hardware peripherals and enhancements for Atari 8-bits. We also had the P:R: Connection which allowed you to directly connect a standard parallels printer (our Star SG-10) to the SIO port.

By default, Atari 8-bit computers used the SIO (Serial Input/Output) port for all peripherals. For its time, this was a pretty advanced port, similar to USB in many ways. In fact, it is my understanding that several of the designers of SIO went on to work on the USB standard in the 90s.

The serial port had a maximum speed of 19,200bps, or about 2.3K per second. That may blow the doors off the speed of a Commodore 1541 disk drive (about 300 byes per second), but it is not great. At 2.3K per second it would take about 40 seconds to copy a single-sided disk.

With a US Doubler the speeds went higher, much higher. One oddity of the Atari 8-bits, due to its POKEY chip handling both sound and IO, was that as data was being transferred you could “hear” it through the TV/monitor speaker. You’d hear bloop, bloop, bloop as chunks of data were loading. With a US Doubler it was more like braaaaap, braaaap, braaap. Rather than lazy beeps it sounded like a machine gun.

According to a small amount of internet research, the US Double achieved its speed increase using a combination of raising the transfer speed (which they now called UltraSpeed) to 54,000bps and special ordering of sectors on a disk to allow them to read/write faster. I’m sure some readers out there knows more specifics, so please leave it in a comment to share with others.

Installing the US Doubler in the drive required opening it up and replacing some chips. I don’t believe any soldering was necessary

With the US Double in place, any DOS could now see the 1050 as a true double-density drive. However, to get the fast speeds, you had to use SpartaDOS.

Unlike the Commodore 64, which could access a disk drive directly because it had a DOS embedded in the drive itself, Atari systems had to load DOS from the drive first. This allowed for lots of different types of DOS, from menu-based ones such as the popular DOS 2 and 2.5 from Atari itself to command-line ones such as DOS XL and then SpartaDOS.

The first version of SpartaDOS was not well received because it had limited compatibility with DOS 2 formats. But SpartaDOS 2, also known as the SpartsDOS Construction Set, was great because it could read and write directly to DOS 2 disks when necessary (it did require an XL/XE, though). That and version 3 were the ones I used the most.

Essentially SpartaDOS was like MS-DOS for an Atari 8-bit. The commands were all similar. You’d type “DIR” to get a directory, for example (generally you typed stuff in all uppercase in those days) or COPY to copy files. A couple cool feature is that it supported subdirectories and file timestamps, also like MS-DOS.

I also seem to recall that SpartaDOS made use of “hidden” RAM in the 800XL to allow it to load from BASIC without wiping out your program. When you typed DOS from BASIC that would usually load up the DOS system and erase your BASIC program in the process. But SpartaDOS would load its command prompt and allow you to use some simple commands without destroying your program, a really nice feature. I think DOS XL, another command-line DOS, could also do this though.

SpartaDOS has continued to be developed through the years culminating in SpartaDOS X, a cartridge that you can leave plugged in to give you an advanced DOS, even with hard drive support!