The CW Plus is a programming service operated by The CW, the joint venture between the CBS Corporation and Time Warner (through its Warner Bros. Entertainment division) created in 2006 through the de facto merger of The WB and UPN.
The "Plus" in the service's name references its intended service areas, the 110 smallest markets among the 210 U.S. television markets ranked by Nielsen. The service mixes The CW's primetime, daytime and Saturday morning programming, with first-run, second-run and brokered programs currently available in broadcast syndication that were acquired by the network that fill out the rest of the schedule; for this reason, since The CW handles programming for the service, it is a cost saver for its affiliates as they don't have to shoulder the responsibility of having to acquire an additional 18 to 24 hoursnote of programming.
The CW Plus can pretty much trace its origins all the way back to the launch of The WB, one of its predecessors, which had trouble gaining affiliates in several mid-sized and smaller markets prior to its launch in January 1995. Recognizing this potential issue beforehand, Time Warner reached an affiliation agreement with fellow WB part-owner Tribune Broadcasting in December 1993 to make the network available nationwide via the national superstation feed of Tribune's flagship station and The WB's Chicago affiliate WGN-TV (the national channel is now known as WGN America, which eventually became a regular cable channel in December 2014, when it dropped most remaining WGN-TV programming) to buy the network time to acquire more affiliatesnote .
While it was able to affiliate with additional stations (mainly remaining independent stations and existing UPN affiliates) in the few years following its launch, co-founder/original president Jamie Kellner wanted a more local presence for The WB, but realizing that gaining affiliates in smaller markets that had at most four commercial stations (which were already affiliated with one or more of the Big Four networks, leaving the only option for The WB to shoehorn its programming in late-night or other off-peak timeslots) would be troublesome. To clear up these bugs, in 1996, Kellner announced he would launch a cable channel similar to Foxnet which he launched in 1991 as Fox's original president to bring WB affiliates to these less urbanized areas. Russell Myerson (who joined The WB in 1997, after a three-year tenure as the Game Show Network's original president) helped Keller bring this idea to fruition, partnering with IBM to develop a data network to digitally transmit advertisements, promos, station IDs and logo bugs for the feed's affiliates to headends in each market, and a specialized wireless computer system (known as a "station in a box") reimbursed by The WB to the feed's affiliates that downloaded, stored and inserted advertising directly to the appropriate affiliate via satellite over the national feed. The WB trafficked ads, programming feeds and inserted ads and logo bugs to individual affiliates that also sent advertising over the Internet to the network's Los Angeles offices.
This "national" feed launched on September 18, 1998 as The WeB (which was renamed The WB 100+ Station Group the other meaning behind the "Plus" in its successor group's name in March 1999), with 80 cable-exclusive affiliates, the largest station group launch in American television history. Ironically, the launch of The WB 100+ may have been responsible for the eventual downfall of its parent network and the WGN national channel's eventual Network Decay. Tribune and Time Warner mutually agreed to drop WB programming from the WGN superstation feed in October 1999note , a move specifically cited behind the loss of a whopping 19% of The WB's household audience, busting The WB to sixth place in the network ratings (behind UPN) during the 19992000 season; WGN's coverage of the Chicago Cubs, White Sox and Bulls could not save the superstation feed from falling behind other cable networks after it lost access to WB programming, culminating in its Retool as a traditional cable network in December 2014. By the mid-2000s, The WB 100+ added a few broadcast affiliates to its portfolio, both through main channel and subchannel affiliations.
After CBS and Time Warner decided to fold The WB and UPN and merge their programming onto the new CW network in September 2006, several elements taken from The WB were utilized by The CW, including the small-market programming feed concept, which was restructured as The CW Plus. The CW (along with MyNetworkTV) were the first major U.S. commercial networks to fully take advantage of digital multicasting to make their programming available to smaller markets that were missing an in-market network affiliation on cable via stations from other markets. However, while it doesn't have as many as it did when The CW launched, The CW Plus still has a few cable-exclusive affiliates as well as a small number of primary channel affiliatesnote . The CW Plus also differs from The WB 100+ in that it doesn't use made-up call letters in a widespread manner, something The WB 100+ had to do to for identification purposes to count viewership towards Nielsen diary ratings in each market; instead most CW Plus affiliates identify by a brand namenote . While it initially used the same infrastructure as The WB 100+, The CW began passing on the responsibility of ad trafficking for The CW Plus to its affiliates in September 2009.
The CW Plus began broadcasting in High Definition in June 2012, although HD availability depends on the market, as many subchannel affiliates are still broadcasting in the 480i standard definition format; however, even in these instances, The CW does provide a default CW Plus HD feed for cable providers carrying an affiliate available OTA in SD only.
Currently, the largest market with a CW Plus affiliate is Brownsville-McAllen-Harlingen, Texas; the largest market with a cable-only affiliate is Traverse City, Michigan. If you want to talk about the largest cities who have them without media market rankings, those cities are Charleston, South Carolina and Cincinnati, Ohio.