Editing Personal Jukebox (section)

==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 computing|24-bit]] [[Motorola]] 56309 DSP running at 33 [[MHz]]. The MP3 [[codec]] (which is about 2&nbsp;MB in [[assembly language|assembly]] DSP code) was licensed from [[Thomson SA|Thomson]] and [[Fraunhofer Society|Fraunhofer IIS]].

===Memory===
The PJB has 12&nbsp;MB of [[DRAM]] and 1&nbsp;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 [[booting|bootstrap]].

===Communication interface===
To transfer data, the PJB is equipped with a [[Universal Serial Bus#Proprietary connectors and formats|USB 1.1 Type B connector]]. Inside is a Philips PDIUSBD12 USB peripheral controller, which averages a raw throughput of about 400&nbsp;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 [[display resolution|resolution]] of 128×64 [[pixel]]s (2:1 [[ratio]]) at a diameter of 3&nbsp;inches (76.2&nbsp;mm). Later versions of the PJB also featured a [[backlight|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 :-). Upper case accented characters are rendered unaccented because that looks better within the font's 9-pixel height. There are some glyphs in the range 0 to 31, used for the symbols on the screen.

===Hard drive===
While flash players could store between 32 and a maximum of 128&nbsp;MB at the time, the first PJB could store 4.86&nbsp;GB of music. While the PJB-100 was updated as bigger drives became available, it was also possible for end users to replace the hard drive (although voiding the warranty in that case).

===Buttons/controls===
The PJB has 6 buttons on the front:
* Left/Previous/Rewind
* Right/Next/Forward
* Up
* Down
* Play/Pause
* Stop/Power off

Volume is adjusted by a wheel on the unit's right side, using a [[Digital data|digital]] mechanism (it can be turned indefinitely). It also is possible to click or push the wheel, which pauses playback and turns the unit off after about one minute. When the unit is powered off and the wheel is pressed for a few seconds, playback resumes. This also works when the buttons are locked, in case the main controls cannot be easily accessed.

On the same side is also a small switch which locks the unit’s controls (except for the wheel).

===Battery and power supply===
The PJB is not powered by [[dry cell|dry cell batteries]] like most other players at the time of its development, but by a provided HanGo [[Lithium ion battery]]. HanGo sold a more powerful 1600 mA battery to be used in the PJB.

The PJB includes a 5&nbsp;V [[power supply]] which charges the battery and enables playback without a battery in the unit at all. The charging control circuit for the battery is built into the PJB itself, not the power supply, so the use of a replacement power supply requires only the proper voltage and sufficient current capacity.