An earlier version ran on an IBM 1440 or IBM 1460 Data Processing System and the IBM Service Bureau Corporation offered a proprietary version, Call/ATS, which ran on IBM 1440 systems or on IBM System/360 DOS systems.
ATS/360 was designed exclusively for IBM 2311 and IBM 2314 direct access storage facilities, for online "Working storage" and "Permanent storage" and for IBM 2400/3400 tape drives, for offline "Rollout/Rollin" (Permanent storage backup/restore) and "Format and print" tapes.
An IBM hardware RPQ provided the IBM 1403 Model N1 printer's TN print train with characters which simulated the IBM Selectric typewriter Courier 72 type ball characters identically, thereby allowing machine printed documents to be manually corrected, or for manually inserted text, as required.
An IBM program RPQ added support for the IBM 3330 direct access storage facility, and this PRPQ was applied by most users of ATS/360 which had migrated to early IBM System/370 processors. Essentially, this PRPQ appended selected instances of the canonical Load Halfword (LH) instruction—which implicitly featured "sign extension" from the halfword's high-order bit, conceptually bit 15, to the remaining 16 bits of the specified general purpose register, conceptually bits 31 to 16—with a logical and (N) instruction, which specified a "mask" of 0x0000ffff, and which eliminated the effect of the bit extension. This, then, allowed for 16-bit disk block addresses, which could later be converted into the expected and required CCHHR format. This PRPQ was also applicable to IBM 3350 direct access storage facilities which were operated in 3330 compatibility mode, and which sacrificed 117 MB of a native 3350's 317 MB total capacity in order to implement compatibility mode—two 100 MB 3330 equivalent drives on one 3350 drive).
ATS/360's input/output operations utilized EXCP exclusively. Task switching was accomplished asynchronously as an extension of ATS/360's EXCP appendages and synchronously as an extension of ATS/360's Type 1 Supervisor Call instruction (SVC 255), OS Nucleus control section IGC255. Thereby, ATS/360 could support quite a number of online (terminal) and offline (peripheral) tasks even on PCP, which otherwise supported just a single task. However, most ATS/360 systems were run in a partition of MFT/MFT-II or in a region of MVT, as the offline "format and print" tapes required a separate printer partition/region to physically print these, although the tapes, themselves, could be created under ATS/360, itself.
ATS/360 provided its own and file formats. Offline "format and print" tapes could be printed using standard OS utilities as these tapes were compatible with BSAM, although these tapes were created using EXCP.