The Explorer 8300 is a digital video recorder (DVR) manufactured by Scientific Atlanta and used by many digital cable companies. It works like a regular cable box with DVR capabilities and features an 80, 160 or 320 GB PATA internal hard drive. Some versions can also be used with an external SATA hard drive through the eSATA connector on the back. The firmware/software generally comes from one of two sources: the Scientific Atlanta Resident Application (SARA) or the PASSPORT software from Aptiv Digital (a spin-off of Pioneer). The choice of firmware is determined by the cable operator and the equipment available at the cable head-end.
Another model, the 8300HD, is a DVR capable of displaying and recording high definition (HD) as well as standard definition (SD) cable television signals. The 8300HD is generally equipped with the 160 GB PATA internal hard drive that can hold ~ 90 hours of SD or ~ 20 hours of HD programming. The 8300HD also comes with an HDMI port versus the DVI port on the older 8000HD model. The 8300HD also will (current software versions) output RF, RCA Composite, S-Video, and Component Video (SD & HD) simultaneously, which the 8000HD could not.
Still another model, the 8300HDC, has the same functionality as the 8300HD. However, it includes a multi-stream cableCARD. The box is a host for the card, which authorizes the box for use. Security protocols are contained within the card instead of within the set-top box itself (known as "separable security"), as it had been in the past. This was done to be in compliance with the U.S. Federal Communications Commission (FCC) mandate that all new set-top boxes employ separable security.
The HDMI implementation does not work with all splitters, switches, and switching receivers/converters.
In the United States, these converter/tuner boxes are generally owned by the cable company and rented to cable subscribers. In Canada, they are either owned by the subscriber or rented from their cable company. Those purchased through auction sites such as eBay must be authorized by the cable service provider by giving them the MAC address of the device so that it can be added to your account. They are not however required to allow you to use this equipment, but if you opt to do so they will not be responsible for any service issues you may have.
There is quite a bit of misunderstanding regarding FCC regulations Title 47, Sec. 76.1201, which states the following:
No multichannel video programming distributor [Cable Co] shall prevent the connection or use of navigation devices [converter boxes] to or with its multichannel video programming system [Cable TV], except in those circumstances where electronic or physical harm would be caused by the attachment or operation of such devices or such devices may be used to assist or are intended or designed to assist in the unauthorized receipt of service.
The above quote applies to devices such as third-party digital video recorders (such as TiVo), and not to contracted second-party equipment such as the Scientific Atlanta 8300 converter box. The reason cable providers are not required to add these boxes as customer-owned equipment (such as they can do with cable modems) is that these boxes are NOT available for retail purchase in the United States, and if they are being sold by a private party, then they have been stolen from the cable provider that owns the box. A cable provider cannot be compelled by any FCC regulation to aid in the illegal use of stolen property.
External expansion ports 
Certain versions of the Scientific-Atlanta Explorer 8300 (the 8300 HD, 8300 MR, and 8300 HD-MR) DVRs are compatible with external SATA drives so that you can expand the amount of recordable hours of programming that can be stored. At this time there are eSATA drives from Apricorn, Western Digital and Seagate. Cable companies have a choice between running their 8300 DVR boxes on SARA, Passport, or their own customized software. Several providers currently support external SATA drives, including Time Warner, Comcast, Cablevision, Rogers and Charter. Seagate's consumer line of external SATA (eSATA) drives are supported, such as their DVR Expander drives are compatible. Western Digital offers My Book AV, which is similar to their My Book series of external hard storage, but specifically tested to be compatible with the Explorer 8300 series of DVRs (8300, 8300 HD, 8300 MR, and 8300 HD-MR). Many external eSATA enclosures will work with the Explorer 8300 series of DVRs with generic hard drives besides those specifically certified to do so.