CHUM's studios are co-located with TSN at 9 Channel Nine Court in the Agincourt neighbourhood of Scarborough (with auxiliary studios located at 250 Richmond Street West in the Entertainment District of downtown Toronto), with its transmitter array located in the Clarkson neighbourhood of Mississauga (near CFRB's own transmitter array).

The station, operating from 1947 in studios at 225 Mutual St.,[6] broadcast a format typical of the late 1940s, with a combination of information, music, and sports.

When CHUM was about to debut, Leary told the press that the new station would be known for community service and in-depth news, in addition to live talent and the most popular phonograph records.

Less than three years after Waters acquired the station, and soon after bringing the new full-time transmitter online, a major programming change was made.

On May 27, 1957, at 6 AM, Waters switched the station to a "Top 50" format that had proven itself popular in some U.S. cities and issued the first CHUM Chart that day.

Later additions to the CHUM DJ lineup included Duff Roman and Brian Skinner, both of whom came from rival Toronto rocker CKEY (then owned by Jack Kent Cooke).

In the late 1960s and early 1970s, CHUM DJs included Duke Roberts (also known as Gary Duke for a time), Johnny Mitchell (better known today as Sonny Fox), J. Michael Wilson, Tom Rivers, Scott Carpenter, Jim Van Horne, John Rode, Don Reagan, John Majhor, Mike Cooper, Daryl B, Terry Steele, Mike Holland and morning man Roger Ashby.

The change also discontinued the CHUM Chart, which ended the week of June 14, 1986, with Madonna's "Live to Tell" as the final Number 1 song.

[14][15][16][17] By January 1989, the station had evolved into a brighter adult contemporary format ("Toronto's Soft Rock"), focusing on pop hits from the past decade and dropping much of the older music.

[19] On September 1, 1989, at 5 p.m., CHUM adopted an oldies format, drawing heavily on its previous Top 40 reputation to cater to the fans of that era's music.

[22] In November 1997, CHUM obtained the radio broadcast rights to Toronto Blue Jays baseball from CJCL beginning in the 1998 season, resulting in a shift towards sports programming on the station.

Noted Canadian sportscaster Jim Van Horne, who had recently left TSN, was the network's marquee host.

The Team 1050 morning show was made up of former TSN host Paul Romanuk, longtime CHUM sportscaster Brian 'Henny' Henderson and Mike Richards.

"The Team" network did not prove successful, especially in Toronto, where CHUM struggled against long-time sports station The Fan 590 (CJCL).

[30] At 3 p.m. on August 27, 2002, the montage that closed down "1050 CHUM" reintroduced the oldies format, followed by the Elvis vs. JXL Remix of "A Little Less Conversation" and Presley's "All Shook Up".

[31][32] [33] The station reverted to a playlist of music (along with occasional liners and identifications) that were popular in CHUM's 50s-to-80s Top 40 heyday.

That same year, CHUM commemorated the 50th anniversary of the launch of its rock and roll format, the highlights of which included vignettes and specials throughout the year, as well as anniversary celebrations on May 26, 2007 that included an open house at CHUM's studios at 1331 Yonge Street, in conjunction with Doors Open Toronto, and a concert at Nathan Phillips Square.

[38][39][40] The change came a few weeks after the CRTC revised its formatting regulations to permit oldies music on FM radio for the first time,[41] although at the time of the change no Toronto-area FM station had performed such a flip (CHBM-FM and Hamilton's CING-FM both adopted a classic hits format later in the year).

CKOC in Hamilton retained a more traditional AM oldies format, while oldies/adult standards station CFZM marketed itself as an alternative as well.

On that same day, host Ann Rohmer (a fine broadcaster, by the way) had to apologize to her viewers because they were having technical difficulties with their picture.

Average cumulative listening hours from spring 2021 through summer 2022 were lower than every surveyed Toronto station except CFPT-FM.