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ATA hard drives compared


Parallel vs. Serial ATA
— 1:19 AM on March 19, 2003

STORAGE SPEED is currently one of the most critical bottlenecks for system performance, especially when paired with today's high-end processors and high-bandwidth platforms. While mainstream users in particular seem more impressed with how much storage capacity today's high-end hard drives offer, these new drives also boast much improved performance, lower noise levels, and larger caches.

Right now, the ATA hard drive landscape looks pretty good, and it's about to get even better. Current ATA hard drives use the ATA/100 and ATA/133 specs, which are limited to transfer rates of 100 and 133MB/sec, respectively. These drives use bulky 80-pin ribbon cables that clutter case interiors and interfere with internal air flow, but help is on the way. The new Serial ATA standard promises transfer rates of up to 150MB/sec using thin, flexible cables might make some wonder how they got by with IDE ribbons at all.

Already, Serial ATA has many of us referring to older ATA/100 and ATA/133 standards as "parallel ATA," but is Serial ATA really all that? And just how fast are today's high-end ATA/100 and ATA/133 hard drives, anyway? We've rounded up high-end parallel ATA and Serial ATA hard drives from Maxtor and Seagate, and a parallel ATA drive from Western Digital and run them through a brutal gauntlet of performance tests to find out. Read on as we discover which parallel and Serial ATA drives rise above the rest and emerge from our benchmarking melee victorious.

The specs
Before we get this benchmarking bonanza started, let's take a moment to go over some of the key differences between traditional ATA drives and the Serial ATA 1.0 standard.

Maximum transfer rate (MB/sec) Signaling voltage (volts) Devices per channel Pins per channel Cable diameter (inches) Maximum cable length (inches)
ATA/133 133 5 2 40 2 (flat ribbon)
0.5 (rounded)
18
Serial ATA 150 0.25 1 7 0.31 40

Performance-motivated users will want to note that, theoretically, the current Serial ATA generation is capable of transfer rates as high as 150MB/sec. Of course, finding a hard drive that can keep up with those speeds is going to be difficult, especially since current 7,200-RPM hard drives have trouble saturating even an ATA/100 interface, which is theoretically capable of transferring data at up to 100MB/sec.

Western Digital is coming out with a 10,000RPM Serial ATA drive that should be able to take advantage of more of Serial ATA's theoretical peak transfer rate, but it's doubtful drives will bump into the 150MB/sec barrier in the near future.


The impossible-to-find power adapter

Though Serial ATA offers a higher peak transfer rate performance than the fastest parallel ATA standard, Serial ATA's signaling voltage is just 0.25V, one twentieth that of parallel ATA. Such a low signaling voltage makes Serial ATA an attractive technology for mobile devices, but I can't imagine that the average desktop user will see much benefit from Serial ATA's lower power consumption. Corporate IT types may appreciate Serial ATA's potential for lower power consumption for multi-drive RAID arrays that are constantly active.

Those looking at building multi-drive Serial ATA systems should note that the Serial ATA standard supports only a single device per channel. This arrangement annoying master/slave relationships that force bandwidth sharing with parallel ATA connections, but motherboard and add-in card manufacturers will need to double the number of ATA ports and channels to give users support for the same number of devices. Thankfully, Serial ATA ports take up a fraction of the space required by their parallel equivalents.


Serial ATA's seven data and 15 power pins


Serial ATA's keyed power (left) and data (right) plugs

Perhaps Serial ATA's most anticipated feature is its new cable standard, which uses only seven data pins per channel. With only seven pins per channel, Serial ATA cables make IDE ribbons look massive. Even those fancy rounded IDE cables look a portly next to Serial ATA's sexy, slender figure.


Serial ATA, rounded parallel ATA, and ribbon parallel ATA cables


Serial ATA cables are thin, really thin

Not only are Serial ATA data cables thin and flexible, the standard also works with cable lengths more than twice as long as standard IDE ribbons. I can't think of any case configurations that would require 40 inches of Serial ATA cabling to connect a single device, but external devices could benefit from support for extra-long cables.

Now that we know what Serial ATA is all about, let's move on to the drives.