were not binary compatible with the Classics, but would transparently run Classic code via an emulator, one that HP integrated into the MPE XL operating system. (Classic code could optionally be translated to native PA-RISC code via OCTCOMP, the Object Code Translator/COMPiler ... such code ran at native speed, but was still subject to Classic stack and memory size limitations). The earlier "Classic" machines were based on a custom CISC processor. From about 1988 onward, HP 3000s using PA-RISC processors began shipping in volume. By 1995 these PA-RISC systems effectively displaced the older family of machines from use. As with all technology shifts, there remained a significant residue of older machines in service. Even today, original Classic 3000s work in production in a few locations. HP 3000 and many HP 9000 machines used the HP Precision Bus. The PA-RISC based HP 3000's operating system was written primarily in Modcal, HP's extended version of Pascal. Large portions of the earlier MPE V operating system, written in SPL, are still used as part of MPE XL and MPE/iX on PA-RISC. A few subsystems (e.g., TurboIMAGE) are written in PSPL (Portable SPL). A small portion of MPE XL and MPE/iX is written in PA-RISC assembly language. The 3000 series operating system was originally styled the Multi-Programming Executive, MPE (later called MPE XL and then, after POSIX compliance was added in versions 5.0-5.5, MPE/iX). The earliest versions of the system used only HP's proprietary SPL systems programming language and BASIC. These System 3000s used a command-line interpreter, with a three-level hierarchical file system, and utilities such as compilers would resemble "run fortran.pub.sys" rather than allowing programs to be run as keyword commands. Later the systems gained a wide range of languages including COBOL and FORTRAN, Pascal, C, and even a version of RPG to assist in winning business away from IBM. People who used the HP 3000 noticed from the 1970s onward that machines were more reliable compared to other mainframe and minicomputers of the time. The ability to recover from power failures - automatically and seamlessly when power was restored - was a notable feature that sold many systems versus IBM computers. At times the HP 3000 suffered from peripheral support delays or gaps caused by HP's decision to delay supporting, or not support at all, some peripherals on the HP 3000 platform—some of which were supported on the identical HP 9000 hardware.