Unlike modern websites and online services that are typically hosted by third-party companies in commercial data centers, BBS computers (especially for smaller boards) were typically operated from the SysOp's home. As such, access could be unreliable, and in many cases only one user could be on the system at a time. Only larger BBSs with multiple phone lines using specialized hardware, multitasking software, or a LAN connecting multiple computers, could host multiple simultaneous users.
The first BBSes used homebrew software,^{[nb 1]} quite often written or customized by the SysOps themselves, running on early S-100 microcomputer systems such as the Altair, IMSAI and Cromemco under the CP/M operating system. Soon after, BBS software was being written for all of the major home computer systems of the late 1970s era - the Apple II, Atari, Commodore and TRS-80 being some of the most popular.
A few years later, in 1981, IBM introduced the first DOS based IBM PC, and due to the overwhelming popularity of PCs and their clones, DOS soon became the operating system on which the majority of BBS programs were run. RBBS-PC, ported over from the CP/M world, and Fido BBS, created by Tom Jennings (who later founded FidoNet) were the first notable DOS BBS programs. There were many successful commercial BBS programs developed for DOS, such as PCBoard BBS, RemoteAccess BBS, and Wildcat! BBS which had early roots from the Colossus BBS started by the author of the popular shareware communications program Qmodem. Some popular freeware BBS programs for MS-DOS included Telegard BBS and Renegade BBS, which both had early origins from leaked WWIV BBS source code. There were several dozen other BBS programs developed over the DOS era, and many were released under the shareware concept, while some were released as freeware including iniquity.
During the mid-1980s, many sysops opted for the less expensive, ubiquitous Commodore 64 (introduced in 1982), which was popular among software pirate groups. Popular commercial BBS programs were Blue Board, Ivory BBS, Color64 and CNet 64. In the early 1990s a small number of BBSes were also running on the Commodore Amiga models 500, 1000 and 1200 (using external hard drives), and the Amiga 2000, Amiga 3000 and Amiga 4000 (which had built-in hard drives). Popular BBS software for the Amiga were ABBS, Amiexpress, StormforceBBS, Infinity and Tempest.
MS-DOS continued to be the most popular operating system for BBS use up until the mid-1990s, and in the early years most multi-node BBSes were running under a DOS based multitasker such as DesqView or consisted of multiple computers connected via a LAN. (Around 1990, OS/2 came out with "preemptive multitasking" of DOS, an alternative to DESQview for multi-node BBS.) In the late 1980s, a handful of BBS developers implemented multitasking communications routines which, although run under MS-DOS, allowed multiple phone lines and multiple users to connect to the same physical BBS computer. These included Galacticomm's MajorBBS (later WorldGroup), eSoft TBBS, and Falken. A lot of the code for the BBS systems was still written in Assembler or Pascal, There was only a minority of C code.
By 1995, many of the DOS-based BBSes had begun switching to modern multitasking operating systems, such as OS/2, Windows 95, and Linux. TCP/IP networking allowed most of the remaining BBSes to evolve and include Internet hosting capabilities. Recent BBS software, such as Synchronet, EleBBS, DOC or Wildcat! BBS provide access using the Telnet protocol rather than dialup, or by using legacy MS-DOS based BBS software with a FOSSIL-to-Telnet redirector such as NetFoss.