A while back I wrote about SCSI.
Personally, I love SCSI. Its intelligent, fast, and efficient. Standard
parallel ATA is just plain dumb. With the new Serial ATA specification,
however, they've given ATA more of a brain.
First of all, I'd like to voice my largest complaint about the
Serial ATA protocol - it's being called "ATA/1500." They rate it at
1500 Mbps (which for some reason comes out to 150 MBps). This is just
like FireWire being rated at 400 Mbps and USB 1.0 at 12 Mbps. And it's
just the opposite of the MBps (megabytes per second) ratings for
SCSI and UltraATA.
Why can't developers decide on a standard set of units? People are
shouting about how much faster Serial ATA/1500 is than UltraATA/100. At
first glance, it looks like its 15 times as fast, but you have to deal
with the difference between bits and bytes. ATA/1500 is only 50% faster
than UltraATA/100. This is still significant, but it involves confusing
advertising methods.
Serial ATA is a point-to-point process. This is going even further
away from SCSI than where ATA is now. Instead of having sixteen, or
seven, or two devices (master and slave) per port, Serial ATA can only
have one device per port. A controller card would have between two and
six ports with a four pin connection for each. Hubs are not allowed.
This is probably not a bad thing, as it is easy to troubleshoot bad
cables and devices without worrying about device interactions.
The current parallel ATA cable uses 80 lines and a 40-pin connector.
26 of these 40 wires are data lines (the rest, presumably, being
grounds). As the Serial ATA cables have four conductors, the cables are
very thin. This means that it is feasible to have a separate cable for
each device without the insides of the computer becoming cluttered with
excess cabling. It also leads to better ventilation. In Macs this is
less of an issue than in PCs, due to the positioning of the hard
drives, but it still helps. For reference, the Serial ATA cable will be
just a bit larger than an internal CD audio cable.
Serial ATA purportedly has a significantly improved DMA (direct
memory access). Many of the intelligent functions that were unique to
SCSI are in the specification. In addition, the star topology of the
drives allows for reliable RAID systems to be implemented.
Despite this increased intelligence, Serial ATA should be available
at the same price as parallel ATA. Due to its speed and increased
intelligence and the continued low price, it is expected that Serial
ATA could displace SCSI. Maxtor notes that there is no reason why ATA
drives have lower physical specifications, other than those that want
high performance drives usually want SCSI. With Serial ATA it is quite
possible that there will be 15,000 rpm ATA/1500 drives on the
market.
It is interesting to note the relationship between Serial ATA and
FireWire. IEEE 1394 was in the SCSI-3 specification as one of the
"alternate" SCSI types, along with Fiber-Channel. Serial SCSI has been
around for a few years, and despite promised speeds of 150 Mbps (which
were expected this year) they never arrived. Serial ATA has been listed
as an internal-only protocol, like the current parallel ATA, so it
won't be competing with FireWire for external devices.
If Serial ATA proves to be everything it promises, it may mean the
demise of SCSI. Maybe it's worth it.
Andrew W. Hill (a.k.a. Aqua)
has been using Macintosh computers since 1987 and maintains that the
Mac SE is the perfect
Macintosh, superior to all - including the
Color Classic. He is on the
verge of being evicted from the family home due to its infestation of
Macs (last count: about 50). Andrew is attempting to pay his way
through college at UC Santa Cruz with freelance web design and Mac tech
support.
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