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There is another popular(?) mass storage device interface called SCSI. SCSI has its ups and downs, mostly down recently, as the prices of SCSI host adapters and devices remain very high compared to ATA/ATAPI.
SCSI has changed a lot over the years. SCSI is basically a generalized device interface that defines the structure of commands, the way those commands are executed, and the way status is processed. SCSI has many physical interfaces, such as the old Parallel Interface, Fiber Channel, IEEE 1394, and ATA/ATAPI. ATAPI is one of the many SCSI physical transport layers. So an ATAPI device is really a SCSI device using a simple, cheap and high speed physical interface.
If you are looking for the SCSI command set used by ATAPI CD-ROM or DVD devices then you should go to the T10 site and find the MMC or MMC-2 documents. Please note that the old SFF-8020 (INF-8020) document is now obsolete. SFF-8020 (INF-8020) has been replaced by the T13 ATA/ATAPI-4 standard (for the interface and command protocol descriptions) and by the T10 MMC or MMC-2 standards (for the SCSI command set).
The SCSI standards are published by ANSI NCITS Technical Committee 10, or just T10:
What is 1394?
It is a 20 year old idea for a serial data bus to transfer data between mainframe computers. It was first described in an article published by the Association for Computing Machinery (ACM). The basic idea was to transfer data directly from the memory of one mainframe computer to the memory of another mainframe computer. Each computer was assigned a 16-bit identifier and the memory addresses were 48-bits wide. You still see some of this original idea in 1394 today: devices have a 16-bit device number and there is still a 48-bit address field in 1394 packets.
Today the 1394 standards are developed and published by the IEEE. Note that Apple Computer uses the name FireWire for this interface. Apple Computer holds many of the patents that cover 1394 technology.
There are two types of 1394 devices: devices that use Isochronous data transfers such as video cameras and devices that use Asynchronous data transfers such as disk drives. 1394 is, in theory, able to handle both types of devices on the same serial bus operating at the same time.
IEEE 1394, like ATA/ATAPI, is one of the many SCSI physical transport layers. When a SCSI device, such as a disk drive, uses 1394 for the physical transport layer (the device's physical interface) the device should use the SCSI Serial Bus Protocol 2 (SPB-2). This protocol describes hose SCSI commands and status information are transmitted in 1394 asynchronous data packets.
You may also see disk drives that appear to be isochronous devices... Some people seem to think a disk drive could be used as a VCR replacement... If you see one of these, take a close look... It is most likely an ATA disk drive with a 1394-to-ATA converted chip... These 1394-to-ATA converters are known as a "tailgate" or "native bridge" chips.
Be very careful when you read descriptions of 1394... Especially be careful of claims such as "high speed data transfers up to 400MB/sec"... That is 400 MEGA BITS (NOT MEGA BYTES). An this is talking about the absolute maximum data transfer rate for any packet on the bus. SPB-2 is very much like a network packet protocol where about 50% of the packets contain control and status information. The actual DATA transfer rates of 1394 are generally much less than 50% of the bus speed...
( ( BusSpeedInMegaBits / 2 ) / 8 ) = TransferRateInMegaBytes
...under the best possible conditions.
This is what Hale Landis said in 1997 about 1394...
What do you get when a bunch of software people at Microsoft try to design hardware? You get a series of documents named PC 9x (now PC 2000). These documents are an attempt by Microsoft to tell the system builders and hardware designers how to design hardware so that it will be supported by the Microsoft operating systems starting in 1997. If this all sounds a little strange to you, just wait until you read one of the PC 9x or PC 2000 documents!
PC 9x/2000 attempts to replace all existing motherboard sockets and device interfaces with two new serial bus interfaces. One of these is USB, a low speed serial interface for keyboards, mice, modems, etc. The other is a questionable higher speed interface know as IEEE P1394 or just as 1394 or FireWire. There are lots of versions of 1394: 1394-95, 1394.2, 1394A, 1394B, and FireWire (and could be more). One of the problems with 1394 is that it is not currently fast enough to really be used with a hard disk.
In PC 9x/2000, higher speed devices, such as hard disks, tapes and printers, would be attached to 1394 serial bus. So far there does not seem to be a lot of support for 1394 interface disk drives. One of the reason is that such drives will cost much more than existing ATA and SCSI drives (any new disk drive interface will be expensive for the first several years). Another reason is concern that 1394 is not really fast enough to support high speed devices.
Because there are not likely to be any disk or tape devices in the near future that support the 1394 interface directly, there is an effort underway to produce 1394 to ATA/ATAPI interface conversion boards. These small boards are currently know as tailgate or bridge boards. Such a board has a 1394 interface on one side and an ATA/ATAPI interface on the other side. The board also has a microprocessor and some amount of memory (both ROM and DRAM). Estimates for the cost of this board are $20 to $50. Compare this with the $10 or less price of existing PCI/ATA host adapter hardware and also remember that there is only ONE thing that drives the PC industry: COST. This whole thing may just be too expensive.
So what happened between 1997 and 1999?
USB did become standard on all computers and there are some applications of USB that seem to mostly work OK. But 1394 was a failure. There are no native 1394 hard disk drives and only recently a few native 1394 CD-ROM or DVD devices. But this isn't stopping 1394 because it has the support of the digital video folks (like Sony) and the support of Apple Computer. Apple seems to think that they can do what the rest of the PC industry could not afford to do... make USB and 1394 the only interfaces on their future systems.
This is what Hale Landis said in 1999 about 1394...
1394 continues to be the most complex, most expensive, certainly the lowest performance and the least reliable interface for computers and devices. In a time when cost is the most critical issue in PC systems, 1394 is just too expensive. It is far more expensive than SCSI and you can see how many systems use SCSI these days.
Now it is January 2000...
If BlueTooth lives up to its marketing hype it will kill 1394. Why have all those expensive cables and unreliable connectors? It seems BlueTooth should be able to do everything 1394 can do and probably more.
And watch out for very poor, or expensive and poor, technical support for 1394 products. Many companies are probably just now finding out how expensive it is to support consumer electronics products (like 1934 video cameras) attached to computer systems via 1394. This is the thing that will 1394 so expensive, not the initial purchase price for the product, but the vast amounts of money that will be spent answering all those technical support calls!
And did you know that...
( 1 * 3 * 9 * 4 ) * 2 equals ( 6 * 6 * 6 )
... Protect your computer and your valuable data! Don't let 1394 in to your systems! With TEOTWAWKI here soon you can not afford to take any chances!
BIG " ; - ) " HERE!
Page updated 18 Dec 2005.