"Bridging" is the conversion of one type of data interconnect technology to another, for example the conversion of a hard drive ATA/IDE parallel (PATA) or serial ATA (SATA) interface to an interface such as FireWire (IEEE-1394).
This conversion is not just a hardware change of one set of voltage signals to another - it is a complete translation of hardware and software protocols from one domain into another. As such, it requires the use of an intelligent computer - typically a microprocessor or embedded CPU. This tiny computer is kept constantly busy translating commands and data between these two different domains.
Since no hard drives have a native FireWire interface, and drives using PATA and SATA interfaces are ubiquitous in the professional and consumer computer marketplace, it was natural that the two technologies would be wedded to produce a FireWire-capable hard drive product. The consummation of that bond produced a "bridge circuit" which is at the heart of Glyph's FireWire Bridging Technology. And that bridge circuit is what makes a "FireWire Hard Drive" a reality.
The Bridge Circuit
Glyph FireWire products use a variety of bridge circuit designs, determined by which design is most appropriate to the particular product and application. All of our GT Series FireWire products are based on Oxford Semiconductor processors, with a large part using the OXFW911 processor. This marvelous chip integrates an ATA (hard drive) interface with a standard IEEE-1394a link interface, and ties them together with an ARM-7 CPU core. If you're familiar with the use of FireWire in audio recording, you probably already know that Oxford's '911 chip is the world standard high-end solution for ATA-to-FireWire bridge applications.
Our most recent product designs use Oxford's '924 chip, which bridges industry standard Serial ATA (SATA) drive mechanisms to FireWire-800, FireWire-400, USB2.0 and eSATA. The '924 is used in products such as our GT 050Q, and the GT 062.
Firmware
The CPU runs firmware that is "flashed" into the chip during the manufacturing process at Glyph. The firmware is designed to maximize data throughput, which translates into maximum performance of your Glyph FireWire hard drive. At the same time, it maintains high data integrity, to minimize the chances of data loss or malfunction.
Glyph Firmware also identifies the bridge as being part of a Glyph product. This permits us to better service and upgrade your drive in the future.
FireWire Physical Layer
In addition to the bridge chip itself, Glyph bridge circuits incorporate what's called a "PHY" (physical layer) chip, which translates the bridge chip link signals into the signals that travel out the FireWire cable to your computer and other FireWire devices on the bus. Most Glyph products use an Agere PHY, the same PHY technology used by Apple Computer in their high-end computers.
The PHY has a little bit of intelligence of its own, which allows it to signal to the bridge chip when it's been connected or disconnected from another FireWire device or computer. This capability permits the FireWire devices to be connected or disconnected while power is applied and figure out what's going on (what's commonly called "hot-plugging").
FireWire for Hotswapping
FireWire PHY chips are designed to be electrically sturdy — after all, they have to take the electrical abuse of being connected while power is applied. Unlike interfaces such as ATA and SCSI which do NOT support hot-plugging, FireWire does, and thus is a much better choice for hot-swapping of hard drives on a computer.
For more on Glyph's use of FireWire as a hot-swappable interconnect within its products, check out the FireWire Hotswap Technology Page.
Useful Links
Oxford SemiconductorAgere Systems