code (although one or two companies offered after-market modification services to install longitudinal time code). The VO-3800 was largely metal, which made the unit heavy, but still technically portable. The VO-4800 had the same functionality as the VO-3800, but at a greatly reduced weight and size, by replacing many components with plastic. The VO-6800 added the improvement of a long, thin battery standard ("candy bars") that permitted storage of the batteries in a trouser pocket. Common model numbers for these batteries were NP-1, NP-1A and NP-1B. The VO-8800 was the last of the portable VO series to be produced by Sony, and featured solenoid-controlled transport. The Sony BVU series added longitudinal and vertical interval SMPTE time code, balanced audio XLR connectors, and heavier-duty transport features. The BVU-50 enabled recording in the field but not playback, and the BVU-100 permitted both recording and playback in the field. Portable recorders were connected to the camera with a multi-conductor cable terminated with multi-pin connectors on each end. The cable carried bi-directional audio, video, synchronisation, record on/off control, and power. Early studio and all portable U-Matic VCRs had a drawer-type mechanism which required the tape to be inserted, followed by manual closure of the drawer (a "top-loading" mechanism). Later studio VCRs accepted the cassette from a port opening and the cassette was pulled into and seated in the transport (a "front-loading" mechanism). Some U-Matic VCRs could be controlled by external video editing controllers, such as the cuts-only Sony RM-440 for linear video editing systems. Sony and other manufacturers, such as Convergence, Calaway, and CMX Systems, produced A/B roll systems, which permitted two or more VCRs to be controlled and synchronised for video dissolves and other motion effects, integration of the character generator, audio controllers and digital video effects (DVE). In 1976, Sony introduced the semi backwards-compatible high-band Broadcast Video U-matic (BVU) format, with the introduction of the top-loading BVU-200. The original U-matic format became known as low-band. The BVU format had an improved colour recording system and lower noise levels. BVU gained immense popularity in ENG and location programme-making, spelling the end of 16 mm film in everyday production. By the early 1990s, Sony's Betacam SP format had all but replaced BVU outside of corporate and budget programme making. With BVU 800 series, Sony made a final improvement to BVU, by further improving the recording system and giving it the same "SP" suffix as