Version 0.10 was released on March 10, 1998. It used the same design as the pre-release prototype. This made expansion difficult as the binary structure used for network communications would break any time a new variable was added. Due to byte-ordering and struct alignment issues, the code usually couldn’t talk over the network to a system with a different architecture. It was also hopelessly bound to one type of UPS hardware.
Five more releases followed with this design followed. The last was 0.34, released October 27, 1998.
Following a long period of inactivity and two months of prerelease testing versions, 0.40.0 was released on June 5, 1999. It featured a complete redesign and rewrite of all of the code. The layering was now in three pieces, with the single driver (smartups) separate from the server (upsd).
Clients remained separate as before and still used UDP to talk to the server, but they now used a text-based protocol instead of the brittle binary structs. A typical request like "REQ UTILITY" would be answered with "ANS UTILITY 120.0".
The ups-trust425-625 driver appeared shortly after the release of 0.40.0, marking the first expansion beyond APC hardware.
Over the months that followed, the backupspro driver would be forked from the smartups driver to handle the APC Back-UPS Pro line. Then the backups driver was written to handle the APC Back-UPS contact-closure models. These drivers would later be renamed and recombined, with smartups and backupspro becoming apcsmart, and backups became genericups.
The drivers stored status data in an array. At first, they passed this data to upsd by saving it to a file. upsd would reread this file every few seconds to keep a copy for itself. This was later expanded to allow shared memory mode, where only a stub would remain on the disk. The drivers and server then passed data through the shared memory space.
upsd picked up the ability to monitor multiple drivers on the system, and the "upsname@hostname" scheme was born. Access controls were added, and then the network code was expanded to allow TCP communications, which at this point were on port 3305.