The hard drive is truly the unsung hero of PC components. You know the type; the kind of component that labors away in the background while all the fl ashy components like the CPU and videocard get all the credit. Yet the hard drive is the one single component that is used in almost every single task you’ll ever perform on your PC.
Whether you are trying to access folders on your hard drive, surfing the web or copying content from one location to another, your hard drive is constantly in use. Even when you are just sitting in front of your computer, staring at the screen, the hard drive’s platters are spinning furiously as the drive’s read/writer heads eagerly await your next command. The millisecond you click on a folder, these heads leap into action to deliver the data you’ve requested, and as soon as they complete your request, they return back to their “ready and waiting” status. You could say the hard drive is the Labrador retriever of the PC, waiting patiently with its tongue hanging out and tail wagging as you decide what trick you’d like it to perform next. As soon as you toss the bone and say “fetch!” it’s off and running. And the good news is hard drives today are faster than ever before thanks to the successful proliferation of the Serial ATA spec.
This new interface doesn’t offer any major benefits over the old interface, which was called “parallel ATA,” other than that it offers more bandwidth for future drives to take advantage of, and is easier to add to a system due to its smaller cables and lack of jumpers. Parallel ATA drives have to be correctly configured via jumper pins as Master or Slave prior to use, but the newer drives have no such limitation—just plug them in and they work. Nonetheless, eventually all hard drives will use the Serial ATA interface, so if you are in the market for a hard drive today, you’d be wise to consider a SATA drive in order to make your system as future-proof as possible. Plus, drive manufacturers are only releasing their top-of-the-line drives in SATA form these days, so if you buy one, you can be sure it’s the cream of the crop (for now).
What is SATA?
The parallel ATA connection standard for hard drives and optical drives has enjoyed an unusually long tour of duty by PC standards, but it’s clear that the old spec is ready for retirement.
PATA is called a “parallel” interface because multiple bits of data travel along the 40-pin cable simultaneously on separate channels. But the parallel ATA interface tops out at a maximum transfer rate of 133MB per second, due to crosstalk. Crosstalk occurs when electrical signals on adjoining wires interfere with one another. It’s like trying to have a conversation with a friend on a crowded bus while the dumbass sitting next to you is yelling into his cellphone. Because you’re sitting so close to Mr. Cellphone, you can only hear his conversation, so you have to talk louder to make your conversation heard. But then he starts talking louder on the phone, and pretty soon neither of you can hear anything and everyone else on the bus is pissed off. That’s crosstalk, and trying to push data through IDE cables faster just generates too much of it. And because the lasagna-size parallel cable is already too large and unwieldy to accommodate good airflow in today’s PCs, an even wider cable just isn’t an acceptable solution. Fortunately, there’s another way to push data at extremely high rates while eliminating the crosstalk problem: Serial ATA.
Instead of adding more parallel wires and channels, Serial ATA eliminates the problem of crosstalk by using an interface that pumps data through a single channel one bit at a time. Without the worry of electrical crosstalk, these bits can be pushed along the serial cable much faster than across parallel ATA.
The Serial ATA cable uses seven wires, three of which are ground wires, with the other four carrying data. Two of the data wires are dedicated to moving data from the computer to the hard drive (downstream), and two are dedicated to carrying data from the hard drive to the computer (upstream).
Q: What makes a hard drive “fast”?
A: Many factors define a hard drive’s raw speed potential, but the most important is the rotational speed of its platters. All drives store their data on internal platters, and the data is retrieved when the platters spin under read/write heads. The faster these little platters spin, the faster the data can be accessed. Today’s standard desktop drives rotate at 7200rpm, and these drives are very fast. There are also a handful of 10,000rpm drives, which are insanely fast due to their rotational-speed advantage. On the server side of things, where performance is king and money is no object, 15,000rpm drives reign supreme. These drives are the absolute pinnacle of performance, but not practical for desktop tasks due to their high cost and relatively small capacity.
The size of a drive’s onboard memory plays a distinct role in its overall performance as well, with the rule of thumb being “the bigger the better.” Onboard memory buffers range in size from 2MB to 16MB, and drives with these large buffers deliver up to 30 percent faster performance, on average, than drives with smaller buffers. Typically, data is delivered from the buffer as fast as the interface allows, so the more data a drive can wedge into its buffer, the faster it can perform typical desktop tasks.
Q: What is Serial ATA?
A: Take a look at a machine equipped with Serial ATA, and the most striking feature will be the skinny data cables. While skinny cables have a positive impact on a case’s internal airflow, this isn’t the main reason why the PC industry is dropping parallel ATA (and its flat, wide cables) for SATA. The main reason is that the current parallel interface is facing a performance wall.
Parallel ATA cables send data along multiple wires within the same wide ribbon. Each piece of data must travel along the length of the familiar ribbon cable, and arrive at the same time in order to maintain data integrity. In order to get more speed from this scheme, the only option is to push the data to higher frequencies or make the data path wider. That’s where the problems lie. Making the data path wider is impractical, as there are already 80 conductors in the ribbon. And increasing speed adds to the likelihood of data corruption.
Because serial interfaces don’t have to deal with coordinating multiple lanes of data, we’re able to push them to much higher speeds. SATA launched with speeds of 150MB/s, slightly higher than the 133MB/s offered by the fastest parallel ATA spec. 3G SATA drives have already doubled speeds to 300MB/s, and will again to 600MB/s by next year.
Although current hard drive transfer rates fall far short of the maximum throughput of even parallel ATA specs, companies are laying the foundation for the future. You don’t, after all, wait for the traffic jam before you try to build the roads (unless you run the state of California).
Advanced Technology Attachment. This is the parallel interface used to attach hard drives, CD ROMs, and DVD drives to the majority of PCs on the market. The term “ATA” is used interchangeably with the term “IDE.” Officially, there are the ATA-1 through ATA-6 specifications, which usually are written as ‘ATA’, and then the interface’s maximum throughput. For example, the final spec of parallel ATA is ATA/133, which allows for data transfers of up to 133MB per second.
Q: What are the different rotational velocities offered in today’s hard drives, and what are the benefits of each?
A: Today’s desktop hard drives are offered in three rotational speeds. The slowest is 5,400 rpm, with these drives primarily being used for rudimentary storage duties where speed is of little importance. They are affordable since they represent last-gen technology and are not in high demand. The next fastest speed is 7200rpm, which is the norm for today’s desktop drives.
These drives are very fast, and are more than adequate for all but the most demanding desktop users. Finally, for those “demanding” types, there are the 10,000rpm Raptor drives from Western Digital. These puppies are wicked-fast, and are zippier than 7200rpm drives by a wide margin. The only drawback to 10,000rpm drives is that they are currently only offered in 150GB or 300GB capacities, while 7200rpm drives are offered in capacities ranging from under 10GB, all the way up to 1TB!
Redundant Array of Inexpensive Disks. An arrangement whereby more than one hard drive is combined to form a single storage volume. Depending on the configuration, better performance, better security, or both can be attained. The only way to practically double a hard drive’s speed is to add a second drive and divide up the work between them. It’s a process called “R.A.I.D.,” and here we see a four-drive array (the fifth drive is the primary volume).