it, and had single-digit serial numbers. Specifications Measurements: 150×80×26 mm (5.9×3.15×1.0 inches) (W×H×D) Weight: 280g (9.9 ounces), 304g (10.7 ounces) including battery Playback: MPEG-1 Audio Layer 3 (MP3) at bitrates of 8 to 320kbit/s and a sample rate of 44.1kHz (playback support for WAV is in the firmware, but is not enabled - it was used by the developers before the MP3 decoder was licensed from Fraunhofer IIS). Audio signal-to-noise ratio (S/N): >90dB Audio total harmonic distortion (THD): <0.1% Frequency response: 20Hz to 20kHz Audio output power: >50 mW at 32 ohm impedance Hardware Digital signal processor (DSP) The heart of the PJB is its Digital Signal Processor. It controls the hard-drive, buttons, LCD, USB interface and handles MP3-decoding for playback. The PJB uses a 24 bit Motorola 56309 DSP running at 33 MHz. The MP3 codec (which is about 2 MB in assembly DSP code) was licensed from Thomson and Fraunhofer IIS. Memory The PJB has 12 MB of DRAM and 1 MB of flash memory. The DRAM is used to buffer data (between 8 and 12 minutes of music, depending on the bitrate used for encoding) from the hard disk during playback. The buffer allows the disk to be run only intermittently, preserving battery life. When the hard-disk is stopped, battery life is preserved; the ramp-loaded heads also retract from the disk surface, helping to reduce the possibility of damage. The flash memory houses the firmware as well as the bootstrap. Communication interface To transfer data, the PJB is equipped with a USB 1.1 Type B connector. Inside is a Philips PDIUSBD12 USB peripheral controller, which averages a raw throughput of about 400 kB/s. Early prototypes used Ethernet instead of USB for data transmission. USB was used in production models because it was more common than Ethernet on standard home computers in 1998. Display The PJB's LCD has a resolution of 128×64 pixels (2:1 ratio) at a diameter of 3 inches (76.2 mm). Later versions of the PJB also featured a backlit display (the backlight comes on when the unit is powered on, or a button is pressed and turns off automatically after a few seconds). The character set the PJB uses internally is Latin-1 (ISO-8859-1), with some minor variations. One of the Compaq developers stated that "it's missing some of the symbols in the range 160 to 255 (because I got bored when I was creating them