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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.'"
Um, no. Gen 1 SATA is 1.5 Gb/s. Firewire is not faster.
"The defense of freedom requires the advance of freedom" - George W Bush
Actually they said SATA 3 (600 MB/sec) will debut in 2007.
I was a bit confused by this article. They talk as if this thing is the Second Coming of Christ, but then they talk about how desktop pcs are just going to keep taking baby steps. Also at the beginning of the article they say that serial seems to be a step back from parallel (ya think?) but it is faster and better and Oh! Look! An elephant!
Since the site is slashdotted, here are further links about Serial ATA:
Cnet
SATA and ISCSI
Intel Dev Paper
Maxtor White Paper
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.
11*43+456^2
- 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.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.
"The defense of freedom requires the advance of freedom" - George W Bush
Personally, I could give a rats butt about the speed. I don't want SATA so my drives go faster. I want it so I'm not having to spend twenty minutes doing finger gymnastics everytime I need to do _anything_ in my case.
Is it worth upgrading for? No, probably not. But id damn sure is worth waiting an extra few months for that next machine to save the hassel of those f'ing ribbon cables.
jello.
aka aron.
Yes- but AFAIK command queuing is not implemented in a lot of the 1st generation controllers because it can break backwards compatibility with PATA software. Most vendors went for an easy upgrade path instead. Look for command queuing in the next generation of controllers.
"The defense of freedom requires the advance of freedom" - George W Bush
Actually SATA is 1.2Gb/s, but that doesn't change your point.
Slashdot - News for Herds. Stuff that Splatters.
1. You can't HOTSWAP an IDE drive without risking blowing your drive, crontroller, or upsetting the powersupply.
With SATA you can.
2. You can't WARMSWAP an IDE drive, without risking blowing your drive, controller, or upsetting your powersupply.
With SATA you can.
3. IDE still only supports 2, yes 2 drivers per controller, which makes it impossible to do hardware RAID-5. That leaves us with software RAID-5 as our only option.
Who cares when you can get hardware RAID-controllers with 12 ports on one card? What is the great advantage of having the cable be the single point of failure for your whole RAID, like SCSI does?
4. IDE cables can only stretch so far, so even if you could somehow manage to get 8 IDE controllers into a box, for a total of 16 drives, there would still be cable length issues. I think 1 m is max. We need differential IDE :)
Ok, 1m can be a problem for some people. However most people do not have cases larger than 1m.
5. IDE drives are just now able to verify data integrity, but thats good since we can start using IDE drives in servers that don't need 100% uptime.
Err, why is it a problem when it is already fixed as you say?
6. ATA/100 Round IDE cables are already available. In fact I just ordered some that have a UV reflective coating for my next case mod which features a black light. Airflow isn't a big issue, in fact Compaq has been slicing up IDE cables for a long time now to increase airflow.
Round IDE-cables are expensive to produce and still large and inflexible. SATA solves it.
7. The SUSTAINED TRANSFER WRITE RATE of IDE drives is still not fast enough to store uncompressed NTSC video at 60 frames per second, or store high bandwidth Satellite streams.
So get the hardware RAID-controller and start streaming away. Oh wait, hardware RAID for SATA doesn't exist. 3ware is a figment of my imagination.
8a. Size increase (GB's) are not keeping pace with read/write access speeds and simply adding cache RAM and tweaking seek algorithms isn't going to remedy this problem.
You can't blame the interface for that. 150MB/s per drive for 12 drives on one card is way more than any SCSI solution supports -- and way more than current drives need.
8b. As, internal volatile write caches grow larger, the risk of uncommitted writes being lost in a power outage or crash increases.
So turn off the write cache. ATA supports Transaction Command Queueing although not all drives support it yet. By the time SATA drives become available, TCQ should be common.
Finally! A year of moderation! Ready for 2019?
There is a certain elegance to such things as SCA backplanes which ATA (in any incarnation) will never achieve.
Which is another point:
They botched SATA by not including power on the bus, having no standardized connector locations, and (at least so far) having no facility for connection of external devices.
The 1-device-per-wire rule of SATA is another detriment: Sure, the cables are fairly small, but can you imagine the rats nest that would be a 12-device SATA system?
SCSI daisychaining is an easy fix for that, and now-common LVD SCSI is quite able to support this number of devices with a single ribbon. And LVD, by its differential nature, is quite resistant to the electrical problems introduced by slice-and-jacket cable rounding techniques that are all the rage these days..
Oh. And you've got your math wrong, Son:
It doesn't matter if 3ware makes a controller with 12 150MBps ports. The 12-port Escalade 8500 you speak of has a 64-bit 33MHz PCI interface, topping out at no more than a paltry 264MBps to be shared by all connected devices.
If you're serious about throughput, try something like this: Two 320MBps channels on a 64-bit, 133MHz PCI bus. Good for real-world transfer rates in the realm of 640MBps, more than twice that of the 3ware product, while keeping a good portion of the PCI bus free the -other- 30 SCSI devices you've got plugged into it.
And none of this says anything about the benefit of SCSI for the home user:
Just bought a new DVD-R, but don't want to toss your old but dead-solid Plextor? SATA requires you to buy another port. SCSI just requires you to plug it in.
Kid-proof tablet..