Serial ATA Technology Explained

Mike Parsons writes "Explosive Labs has an interesting article on Serial ATA . Here is a quote: 'In the rapidly moving computer industry, there are rarely the kinds of revolutionary changes like what is about to take place in secondary storage segment. Soon the hard drives and configuration methods that have existed since the origins of the personal computer will change forever. The basic IDE technology has been around for nearly twenty years. When the lifetimes of other computer components like CPUs and video are measured in months, twenty years ago seems like prehistory.'"

Comments

Prehistory? Depends on context

[Hentai]

Think about this - how long has RS232 been defined? How long has the PC's parallel (i.e., LPT1) pin-out been defined? How long has the VGA pin-out been defined? How long has the PC keyboard pin-out and protocol been defined? A lot of things change pretty fast; a lot of things stay around forever. It all depends on whether upgrading them is worth the cost in the long run.

Re:Prehistory? Depends on context

[Thurn und Taxis]

For that matter, how long has the x86 architecture been defined? How many /. readers were even alive when the 8086 was released? I know I felt a few grey hairs pop out when a co-worker told me his first computer was a 286. Only superficial changes in computer architecture have happened during our lifetimes. The way we interact with computers is totally archaic, just like the way we interact with banks, cars, washing machines, and televisions is archaic. The world is dying for some clever person to come up with a way to make it just as easy to ask a machine to do something as it is to ask a person to do something.

Re:Prehistory? Depends on context

[dutky]

With one exception, none of the "standards" you mention are either very old or very standard. The exception is, of course, RS-232, which was defined in 1969 by the Electronic Industries Association of Washington D.C. (my home town). All of the others are relative infants:

• The PC parallel port was defined, in a very loose manner, by IBM when the IBM-PC was introduced in the early 1980s. The original PC parallel port was unidirectional and good for little else than driving a printer. While a number of manufacturers offered bi-directional versions of the PC parallel port (including IBM, in the late 1980s, with the IBM-PS/2) no actual standard existed until the release of IEEE-1284, in the mid-1990s, which gives us the modern ECP/EPP option.
• The VGA pin-out dates from the introduction of the IBM-PS/2 in 1988/1989.
• The PC keyboard pin-out and protocol have only been around since the introduction of the IBM-PC, and have undergone at least two revisions, first for the IBM-AT keyboard, and second for the IBM-PS/2.

The reference to IDE having been around for 20 years is a pretty dubious one, unless you count IDE as just a variation on the vernerable IBM-PC expansion bus. (commonly known as the ISA bus) Still, 20 years ago, there was no such thing as IDE, even as a glimmer of a hope in anyone's eye.

Re:Prehistory? Depends on context

[Call Me Black Cloud]

You're correct. Consider the length of time the original male-female coupling system has been around...

This just looks expensive.

[jericho4.0]

The first generation doesn't look that impressive, as shown by the selling points given by the author. Thinner cables, up to a meter long?? Ok, sounds nice, but not worth paying extra for, for my needs. Serial ATA wil debut at 150 mb/s, not really an improvment at all.

The author then goes on to note that the 'roadmap' calls for the 2006 version to run at 600mb/s, which fits nicely with my roadmap to world domination in 2005. ...Ummmm, yeah, we'll see.

Although looking at the list of upcoming products and the manufactures making them, I don't doubt we'll all be useing this in a few years.

Re:This just looks expensive.

[photon317]

The battle between serial and parallel communications is neverending. Show me a Serial WAN connection like a DS3, and I can say "Well, since you never send partial bytes, we could strap 8 of these side by side, send one byte at a time with the bits split up over the 8 DS3s in parallel frames, and we get an 8x speed improvement that's usable by a single connection and no additional latency".

Or show me a parallel bus like IDE, and I can say "Look, having all those data lines next to each other causes additional interference we have to account for, and they're bulky, cost more, overly complex, blah blah. If we just put a serial bitstream on a pair of wires, it would be so much simpler that for the same cost we can turn up the bitrate more than enough to make up for the lost parallelism."

It's all the same. Various communication technologies tend to rise and fall, serial replacing parallel replacing serial replacing parallel ad infinitum. In some cases (like PCI busses) parallel just makes a lot more sense, but in a lot of cases (network stuff, storage stuff especially) there's a tradeoff where both are better and worse than the other in different ways. You could just pick one and stick with it and do you incremental improvements, but the occasional switcheroo provides upgrade revenues and more user "wow" factor and buzzwords.

Re:FIREWIRE?

[cheezedawg]

Um, no. Gen 1 SATA is 1.5 Gb/s. Firewire is not faster.

Re:SCSI?

[stratjakt]

> All of IDE's shortcomings are fixed by SCSI

You mean the oversized 40-conductor ribbon cables are solved by 68 conductor ones?

> If more people used it, it would be a cheaper solution

Heh, sure it would.

> 15k rpm scsi drives get seek times in the low three range--that's three times faster than your average 5400 rpm ide hdd.

And 10x more expensive.

You are the first SCSI fanboy I've ever seen.

Now bring on the cheap!

Personally, I can't wait until it comes out...

[HoneyBunchesOfGoats]

...'cause that means prices will drop on hard disks that I can use.

More Information

[leibnizme]

Since the site is slashdotted, here are further links about Serial ATA:

Cnet

SATA and ISCSI

Intel Dev Paper

Maxtor White Paper

RDRAM Redux

[grendelkhan]

This sounds remarkably like the plugs we got for Rambus RDRAM: serial interface is better than parallel, first gen won't see real performance gains, stick with us kids, this is gonna be really good.

I see a decided lack of Sun, IBM, AMD, or HP listed in the adopters, which leads me to believe that this is much like the above. Sorry guys, I'm not riding the first wave of any new tech on my salary. I'll sit on the sidelines for awhile and see how this pans out.

Re:too bad that

[cheezedawg]

All data goes through the PCI bus

No it doesnt. Data goes through the PCI bus if the address is not claimed by something else along the way. That means that everything from the southbridge up is not limited by the PCI bus bandwidth. That means that integrated SATA controllers (not available until next year) are only limited by the bandwidth between the northbridge and southbridge.

Ever read the actual throughput specs on a drive?

Drive throughput has been steadily increasing, and it is predicted to pass up PATA within a few years, and that is not counting RAID striping or the 8 MB drive caches. Its always desirable for the bottleneck to be the drive rather than the controller.

ridiculous

[tps12]

Why are they wasting their time on this ancient technology? Serial is too slow to sync my damn Palm Pilot. I can't even imagine what it would be like to try and transfer 60GB of media files over it. These companies should just accept that USB is the way of the future (no extra power required either!) and get to work on something that stands a chance of selling.

Re:too bad that

[Magila]

4 of them in RAID 0?

This won't be an issue since SATA is strictly point-to-point, every drive gets it's own 150MB/s link.

Re:SCSI?

[shepd]

>I would like to say that the price of SCSI drives is not 10x more because nobody wants a SCSI drive, but because they are simply more complicated to manufacture and interface.

That was true in 1980. It isn't now. I mean, it costs no more to build a RAID card (witness Promise Ultra Hack) than it does to build an IDE card, and that's massively more complicated than SCSI.

In fact, since all the smarts are moved onto the controller (which is dead simple to make today -- I bought a cheap one for $35 CDN two years ago -- it was cheaper than a cheap IDE card!) the drive itself is less complicated.

>Also, the preformance hit you take going from 7200rpm SCSI to 7200rpm IDE is not noticable at most times, but I suppose i am tolerant because i can wait more than 3 ms seek.

Agreed, but there's more to it than that. IDE requires new interfaces every drive (unless you want to take the horrible performance hit master/slave arrangements incurr). SCSI doesn't. IDE cables can only be 18". SCSI can be quite a bit longer. IDE only works for hard drives and CD-ROMS (and one or two other things). SCSI is for anything. There's more reasons than this to support SCSI over IDE (at the same price), but I think these three would be enough to sway users at the right price.

>SCSI is loud and hot and expencive, just like all preformance computing componants, and thus will never be a consumer standard.

Only because no manufacturer thinks there's a good market if they slap a SCSI controller on their current consumer hard drives. I think there is, and I'd be game to buy one, if they existed, for my next upgrade.

Re:too bad that

[ltwally]

For starters, the PCI spec isn't limited to 133 MB/s. PCI 2.1 specs allow for 66 MHz 64-bit transfers, which equals 528 MB/s. PCI 2.2 specs allow for PCI-X mode, which adds 133 MHz 64-bit transfers: 1056 MB/s.

That being said, it is entirely possible to reach throughputs in excess of 133 MB/s using a PCI bus... though currently most desktop motherboards do not support anything faster than 133 MB/s. In time this will change as NICs, hard disks, and other gear requires it.

And your hard disk performance is barely par by today's standards. IDE drives are currently topping 50MB/s, while SCSI gear is hittin > 70MB/s. Though I am a SCSI man, i can see the future need for SATA. Right now it may be mainly a marketing ploy... But in a couple years it will be a necessity. Parallel cabling is nearing the end of the road.. all those wires in a cable allow for too much signal interference. Serial is the answer. Though it has less wires, the dramatic increase in signal strength allows for insane transfer rates.

Anyhoo.. personally I don't see any reason to go out and buy a new system just to have SATA. At the current it offers few advantages.. but in the not so distant future it will be a necessity for desktop systems. As for me, i plan on going Fibre-Channel SCSI :)

IDE TROLLS: READ THIS

[darkwiz]

SCSI drives are notorious for their noise, heat and vibration levels. These low points are not acceptable at the consumer level. Noise and heat don't matter too much in huge server rooms, but they can quickly become a problem in desktops.

For the time being, IDE isn't going anywhere.
NOISE & HEAT will tend to outweigh (relatively) minor performance gains in consumer systems. (Enterprise hardware is another matter entirely)
sigh....we need to start using those annoying javascripts that make people read the article BEFORE posting.

Absolutely. But this has nothing to do with SCSI, it has to do with the high spindle speeds at the bleeding edge. The card on the underside of the drive is not making that ear shattering racket. They even acknowledge that in your quote.

SCSI is better than ATA. Even SATA. ATA has been trying to catch up by stealing some of the best parts of SCSI (like TCQ). But it just isn't quite as good yet. Quite frankly, I agree with the majority of SCSI zealots: if the damn PC makers would embrace SCSI, then the cost of SCSI would come down to near parity from the volume of sales.

Now, is SCSI better for your average Joe? Maybe not significantly. Neither is 7200 vs 5400, 2MB vs 8MB buffers, or 8.9 vs 9.1 ms access times.

However, if they could use one cable to connect 15 devices in their tower, they'd be alot happier than having the 8 cables they'd need to do it with current IDE tech (let alone IDE's relative inability to be used externally).

Re:SCSI?

[G-funk]

it's got nothing to do with how common it is, scsi is expensive because it raises the percieved value of the product, and it's common knowledge that this "elite"ness of more expensive alternatives to a product aid sales.

In short, it's expensive because they like it that way. There's no shortage of scsi drives, they're not particularly more expensive to produce.

Re:This is a GOOD thing. FINALLY

[NineNine]

This post is an *excellent* example of what watching too much super-fast cutting TV (like MTV) can do to you.

Re:SCSI?

[GooberToo]

Someone mod this guy up. He, "gets it!" SCSI is expensive because it's the premium, top-shelf product. Period. SCSI is expensive for the same reason that diamonds are. Both are highly desired but have no more value than the next drive (be it IDE or rock).

In other words, they are expensive because people want to keep them that way!

Re:SCSI TROLLS: READ THIS

[mosch]

That has nothing to do with SCSI. The only reason it's even remotely related is because people have a tendancy to buy SCSI drives like this one, which is a 15K RPM drive with a 3.2ms seek, and the ability to sustain a 75MB/sec data throughput rate, whereas high-end ATA drives like this one spin at 7200 RPM, have a 9ms seek, and don't list their maximum sustained data throughput rate on the data sheet.

Is IDE appropriate for the desktop? absolutely.

Will retards continue using IDE in applications where SCSI is far more appropriate? definitely.

Does your post make any fucking sense at all? nope.

Am I missing something here???

[Lobsang]

I think I am. Really.

The article seems immensely biased and lacking in technical detail. It also raises some "dubious" points IMHO. Let's see:

- P-ATA cables cannot be longer than 40cm. S-ATA cables can be up to 1m long:

Granted, those cables are annoying. But really, how many times have you felt the need for a cable much longer than 40cm? People with full-sized cases may benefit, but then the author says that the current trend is "small footprint machines". So, why do I need a cable that is bigger than my server?

Also, if you dislike flat cables, buy "rounded" P-ATA cables (available today, just google for it).

- P-ATA connectors are big!

Yes, they are! But you'll require at least twice as many S-ATA connectors, as only one device is supported... In the end, the real state on the mobo is going to be similar.

- One device per controller is an "Advantage".

C'mon... This guy must be joking. I couldn't believe my eyes when I read it! One device per controller is an *advantage*???? Why??? I wish I could add more devices (like SCSI and Firewire) to my curreny P-ATA technology. And then he says ONE is good for me? Don't think so...

- High transfer rates are useful for multi-disk RAIDS.

What kind of RAID? RAID 5 is slow in writes due to the computational power needed to calculate the XOR. Adding bandwidth won't help. And I can't see why or how only RAIDs will benefit from higher throughput.

- Speed:

Granted. It may be faster than P-ATA. But what about established technologies like SCSI and Firewire? I *think* (not sure) Firewire can go much faster than S-ATA in its initial version.

I'm disappointed...

SATA propagates all the crap of PATA

[mnemotronic]

Serial ATA has kept all the truely horrible, obscure, and performance limiting features of parallel ATA (which was originally designed for 40 Mbyte drives), and shoves it down a thin cable. A course in ATA protocols will leave anyone who is computer literate going : You have got to be kidding!! What were they smoking????? The Serial spec has to maintain all kinds of bizarre, obsolete behavior just so that a SATA drive is backwards compatible with old software (i.e. that WfWG 3.11 system you've got tucked away in the closet). Throughout the history of ATA, when drive capacities climb towards the addressable limit of the spec, the protocol is kludged by a team of drunken baboons to extend it for another generation. The SATA committee munched an opportunity to drill a much-needed stake through the heart of ATA and give us a new interface for the next 20 years. Instead we get a change in connectors for a protocol with it's feet firmly encased in the concrete of MS-DOS 2.

Firewire (1394) was killed by Apple's licensing fees and Intel's sudden backstabbing policy change on building it into south-bridge, along with their NIH attitude. There existed working 1394 Device Bay drives over 6 years ago, with OS support from m-soft. 1394 was an attempt to keep the good parts of SCSI protocol, while leaving out as much of the useless stuff as possible (MODE SELECT).

Fibre-channel is still Real Pricey, for the same reason that SCSI is -- "just because". Or, as the hardware vendors say "harrumph, well, it's all about volume".

S-ATA is the Ghetto FC

[Duncan3]

It's real simple, ribbon cables SUCK, they cost more to make then serial so PC makers hate them.

So, here's how it is...

Fibre Channel - 2Mb/s(10Mb coming very soon), 126 drives, 10+ mile range, better then SCSI.

S-ATA - 1.2Mb/s(2.4Mb in 2004), 18" range?, IDE protocols for all your write-only data needs.

S-ATA is the Ghetto FibreChannel, just like IDE is crappy SCSI, expect similar suckiness and low quality to go with the low price and cheaper cables (to make, to buy they will cost more I'm sure).

But again, this is all about the creaper cables, since lets face it 95%+ of the machines out there only have one drive anyway.

Re:SCSI?

[fava]

I quote:
SCSI devices last forever, or until they break,

I can top that:
I will live forever, until I die.

What was your point again?