This software consists of the operator's menu system, self-test routines and device algorithms. Later in production, an option for installation of a miniature hard drive was provided (See MSM, or Mass Storage Module, below). The Unisite is the only programmer that still requires true 720k floppies for non-MSM operation, or updating the MSM's software without the aid of external PC-based software. The Unisite was the flagship model of the Unifamily line, selling for over $35,000 in a typical configuration and staying in active production for at least 20 years. Data I/O, in an effort to make the Unifamily line more attractive to companies with tighter budgets, introduced several other programmers utilizing the same pin-driver technology as the Unisite, all selling for (typically) under $10,000. These included the model 2900, 3900, 3980, and 3980XPi. These units varied in capability, primarily in terms of the number of pin drivers. The basic 2900 featured 44 drivers, while the 39xx series all had 88. Data I/O developed a proprietary multiplexing scheme which allowed Unifamily programmers, equipped with their maximum number of hardware pin drivers, to handle devices with up to 240 pins. Other differences in the series are minor. Models share a common base design and feature the ability to boot and run from floppy diskettes and provide an internal menu. The differences are primarily in features. The Unisite, less than a year of entering production, was revised in the form of a new DIP module, referred to as the 'Site48.' This adapter had 48 pins in its DIP socket, and remained the standard for many years. Its successor, the Site48-HS, is functionally identical, but utilizes solid-state switching for the socket pins instead of the electromechanical relays in earlier adapters such as the 2900 and 39xx series. The Unisites featured 512K of user RAM, standard. Field-installable upgrade kits, consisting of a separate memory board, an appropriate number of 30-pin SIMMs, a mounting bracket and interconnecting cable, were made available to upgrade these early units to 1MB or 8MB. The price for the 8MB upgrade kit was around $495 in the mid-1990s. These early kits required considerable labor to install, including extensive disassembly of the programmer, as the memory board was designed to mount under the main circuit board. In response to these difficulties, as well as improvements in available technology, the Unisite's main circuit board soon received major revisions. These included the removal of