When Intel’s Thunderbolt interconnect was formally unveiled last year, we learned that Apple would have first dibs on the technology. Device makers would be free to build Thunderbolt-compatible accessories right away, of course, but the first computers to employ the uber-fast interconnect would be Macs.
The enthusiast community met this news mostly with a collective shrug. We already had USB 3.0 ports with oodles of bandwidth for external storage devices that were affordable, backward compatible, and readily available. Thunderbolt hardware? Not so much. We also knew that Light Peak, the precursor to Thunderbolt, was conceived as an optical interconnect. Apple’s implementation ditched optical fibers for copper wires, which simply aren’t as cool.
More than a year after Thunderbolt ports made their Mac debut, PCs are getting their first taste. Select Ivy Bridge notebooks are destined to feature the technology, and Thunderbolt-equipped motherboards are already selling online. A closer look is warranted, so we’ve rounded up a couple of motherboards and an external storage box to see what’s what.
You’ve been… Thunderstruck
Before we dip into the PC-specific gear, we should familiarize ourselves with the underlying technology. From a hardware geek’s perspective, it’s pretty slick. Thunderbolt is a point-to-point interconnect with an obscene amount of bandwidth and the ability to transmit both DisplayPort and PCI Express signals along a remarkably thin cable. How much bandwidth? 10Gbps in each direction, per channel. Each Thunderbolt connector carries two channels, bringing the pipe’s aggregate bandwidth up to a staggering 40Gbps, or 20Gbps in each direction.
To put that into perspective, a single USB 3.0 port offers 5Gbps of bidirectional bandwidth. One PCI Express 3.0 lane has 10Gbps of full-duplex connectivity. Thunderbolt beats them both with ease. And all of its bandwidth is usable thanks to a low-overhead packet format, Intel says.
Offering gobs of bandwidth is one thing, but Thunderbolt’s real crown jewel is its ability to map DisplayPort and PCI Express signals to a single “meta-protocol.” Translation is handled entirely by the Thunderbolt controller, allowing the interconnect to remain invisible to the host PC, which sees only the connected devices. Software isn’t required for the controller, but Thunderbolt devices will have their own drivers.
Intel hasn’t revealed exactly how bits are encoded within the Thunderbolt protocol, but we do know there’s a flexible QoS framework tasked with multiplexing the PCIe and DP streams. Depending on the configuration, encapsulated signals may be routed through multiple Thunderbolt controllers before being decoded. As many as seven Thunderbolt controllers can be daisy chained together, and the switch-based architecture supports other topologies, as well.
A domain-based time synchronization mechanism keeps attached devices within eight nanoseconds of each other. That feature will be key to Thunderbolt’s appeal among audio and video content creation professionals. Intel claims Thunderbolt’s low latency as another benefit, although it doesn’t offer any specific numbers on that front.
The Thunderbolt controller chip does all the work associated with the interconnect. It contains a Thunderbolt switch, a PCI Express switch, and adapter ports for DisplayPort and PCI Express. Controllers can come with one or more Thunderbolt ports, and they connect to the host system using a PCI Express 2.0 x4 link. DisplayPort devices hook into the controller via the associated adapter ports.
Although PCI Express is now in its third generation, four gen-two lanes still offer plenty of bandwidth for a whole range of devices, including the I/O peripherals one might expect to find in a Thunderbolt companion hub for notebooks. A hub could easily offer a collection of Serial ATA, USB, and FireWire ports courtesy of auxiliary controller chips. Heck, you could even throw a discrete graphics processor in there. Indeed, we saw a notebook with a Thunderbolt-connected external GPU at the Consumer Electronics Show earlier this year.
The final component of the Thunderbolt equation is the physical interface: the connector and its associated cabling. Mini DisplayPort has been adopted as the connector, in part because it’s interoperable with existing DisplayPort monitors, but also because it’s small enough for the sort of ultra-slim notebooks that seem ripe for Thunderbolt expansion. Electrical cables can span distances up to 3 m and carry as much as 10W of power for connected devices. Optical cables promise lengths in the “tens of meters,” though the device at the other end will need its own power source. Both types of cables use the same MiniDP connector.
If you’re wondering how Thunderbolt can get away with using an electrical port interface for optical cables, the answer is that all Thunderbolt cables are smart or “active.” They include termination electronics at each end to assist with communications. The optical cables will convert electrical impulses into light at one end and back into electrical signals at the other. The reason not all Thunderbolt cables are optical now? Copper Thunderbolt cables are less expensive.
Despite its considerable potential, Thunderbolt still has some limitations. In addition to the seven-device cap on daisy chaining, no more than two DisplayPort screens can be connected at a given time. Those need to be DisplayPort 1.1a or newer displays, by the way. With older DP screens, users may be limited to one display per chain.
A bigger concern is the lack of hot-plugging support in Windows. If you want a Thunderbolt device to be accessible, it needs to be connected when the system is booted. Intel says hot-plugging support is coming in driver updates for Thunderbolt devices. We’ve heard those drivers may arrive as early as this month and that some cooperation is required from the motherboard firmware. Any Thunderbolt device that’s certified for Windows should support hot plugging, Intel says.
Only premium products need apply
Even when hot-plugging becomes a possibility, Thunderbolt will still be face one very big obstacle: price. The only electrical cable you can buy right now comes from Apple and costs a whopping $50. Imagine what Monster will charge for its inevitable gold-plated version.
Admittedly, there are clear reasons for the high cable costs. As we’ve mentioned, the Thunderbolt cable is an “active” one, which likely raises its manufacturing cost. As a result, non-Apple alternatives may not end up being much cheaper, and the optical variants will probably cost even more. No wonder device makers have been selling their products sans cable. Even the four-drive Promise RAID device we used for testing comes cable-free.
At its Thunderbolt press event the day before the Computex trade show in Taipei, Taiwan, Intel told us that second-generation electrical cables will appear in the latter half of this year. These cables will feature more integration in their active circuitry, and they should cost less as a result, about 25% less, according to Intel. $37.50 for a Thunderbolt cable still sounds pretty expensive to me.
The cost of integrating a Thunderbolt controller chip isn’t trivial, either. MSI told us it costs $30-35 to add Thunderbolt to a motherboard, a figure we’ve heard echoed elsewhere. The controller chip makes up the bulk of cost.
Given the relatively high price of entry, it’s no wonder Thunderbolt controllers have only found their way onto a handful of high-end motherboards. The most exotic of those is Asus’ P8Z77-V Premium, which was the first Thunderbolt-compatible board to arrive at the Benchmarking Sweatshop.
As its name implies, the Premium isn’t cheap. Newegg is selling it for $449 right now, which is more than the cost of a mid-range Z77 board and a fully unlocked Ivy Bridge CPU.
The Premium’s payload certainly lives up to the name, though. This thing is loaded with more accessories than a Harajuku girl. In addition to a Thunderbolt port, it comes with extra USB 3.0 and 6Gbps SATA ports, an mSATA slot populated with a 32GB SSD, and four PCI Express x16 slots. The x16 slots are all connected to the CPU via a PLX switch, ensuring that none encroach on the bandwidth available to the Thunderbolt chip, which enjoys a four-lane PCIe link to the Z77 platform hub.
Asus provided us with some interesting details on how it has deployed the “Cactus Ridge” Thunderbolt controller you’ll find on other PC motherboards. The traces between the Thunderbolt chip and its Mini DisplayPort connector are very short—only two inches long, compared to 10 inches for the board’s USB 3.0 controller. To further improve signal quality, the traces are more widely spaced than usual, and they follow smooth arcs instead of the 45-degree corners used elsewhere on the board.
If the Premium is a little to rich for your tastes, Asus also has the P8Z77-V Pro/Thunderbolt. Unlike the Premium, it hasn’t passed Thunderbolt certification just yet. However, we expect the board to cost around $260.
Folks with select Asus Z77 motherboards will also have the option of buying a Thunderbolt PCIe expansion card. Asus expects the card to cost $40 when it becomes available in late Q2 or early Q3. You won’t be able to plug it into any old motherboard, though. The card needs to see the system’s display output, which it can only do via a separate connection to a special motherboard header.
The next motherboard on our Thunderbolt tour is Intel’s DZ77RE-75K. Like the Asus offerings, it uses Intel’s flagship Ivy Bridge chipset, the Z77 Express. You don’t get nearly as many auxiliary peripherals as on the Premium, of course, but the Intel board is still very well equipped, with integrated Bluetooth, Wi-Fi, and additional 6Gbps SATA and USB 3.0 connectivity. It’s also much more affordable than the Premium, with a suggested retail price of $278.
Note that I didn’t just call a $278 motherboard affordable. It’s more affordable, which is sort of like saying a Lamborghini Gallardo is more affordable than an Aventador.
Intel says the DZ77RE-75K’s Thunderbolt chip gets a full four lanes of PCIe 2.0 bandwidth. As on the Asus board, the controller is extremely close to its associated connector.
While the DZ77RE-75K has completed certification testing, MSI’s Z77A-GD80 has not. MSI expects to have the board certified after the Computex trade show, which runs through the end of this week. If you’re feeling adventurous, you can already buy the GD80 on Newegg. The asking price? $269, or $9 less than the Intel offering.
MSI wasn’t able to get us a GD80 in time for this article, but its Thunderbolt implementation doesn’t appear to differ substantially from the other two boards. They all give the Cactus Ridge chip a PCIe x4 link and a choice location next to the MiniDP port.
The promise of Thunderbolt devices
With two Thunderbolt-equipped motherboards at our disposal, the only missing component is a compatible device. A handful of options are already on the market thanks to Apple’s early entry, and more are on the way now that Windows PCs can get in on the action. Promise supplied us with its Pegasus R4, a four-drive external storage device with dual Thunderbolt ports. The second port allows the Pegasus to sit in the middle of a daisy chain of devices. It can’t get enough power from a standard Thunderbolt cable, though. You’ll need to plug this puppy into a wall socket.
The Pegasus R4 has an understated metal exterior marred by a single piece of glossy black plastic. To be fair, you’re not going to be handling the thing enough to leave behind a mess of smudges. I still deposited a few fingerprints on the plastic panel in the course of unboxing the device and setting it up next to my test rack.
Under the Pegasus’ silver skin sits a PMC Sierra SoC with a Promise “enterprise level” RAID engine. The chip is designed to accelerate RAID 5 and 6 arrays, Promise says, and the Pegasus also supports the usual mix of striped and mirrored configurations. The R4 has four drives, and there’s an R6 variant with six.
Each drive is housed in its own 3.5″ sled. The sleds slide into the Pegasus with ease, and the latching mechanism that holds them in place is satisfyingly chunky. You definitely won’t pop one of these out by accident.
Promise claims the R4 is capable of pushing transfer rates as high as 500MB/s, which falls well short of the bandwidth available in a single Thunderbolt port. Even the Pegasus R6’s purported 900MB/s peak data rate is far from fast enough. Of course, the Pegasus relies on mechanical hard drives; our R4 came loaded with 7,200-RPM Hitachi drives, each with a terabyte of storage. Fill the Pegasus with SSDs, and it should get much faster.
Unfortunately, we don’t have a matched set of four SSDs. But we did spend some time benching the Promise box on the Asus and Intel motherboards. They offer identical performance, as far as our test results show. We considered graphing the numbers, but to be honest, there’s little point. The R4’s performance is limited more by the mechanical hard drives within than by the Thunderbolt cable linking it to the system.
With the R4 in its default RAID 5 configuration, we just about broke 400MB/s with sequential reads and writes in IOMeter. Hitting that speed required hammering the drive with multiple concurrent I/O requests. CrystalDiskMark’s sequential throughput benchmark is limited to a single I/O, and it only reached about 330MB/s. We saw similar transfer rates in FileBench, our scripted Windows file copy benchmark.
Had we switched the R4 into RAID 0 mode, we probably could have hit higher speeds, at the expense of redundancy. We still would have been short of stressing the Thunderbolt link, though. The interconnect is really designed to handle multiple high-bandwidth devices alongside a high-resolution DisplayPort monitor.
There’s another thing, too. We ran the very same tests in our Z77 motherboard round-up using a Samsung 830 Series SSD attached to the Z77’s integrated USB 3.0 controller via a Thermaltake BlacX docking station. In CrystalDiskMark’s sequential read speed test, that combo pulled up just 10MB/s short of the R4 on Thunderbolt. The gap widened in FileBench. However, in CrystalDiskMark’s random I/O tests, the USB-attached solid-state drive was at least an order of magnitude faster than the Pegasus array.
It’s not really fair to compare the two—the SSD weighs in at only 256GB, while the R4 config offers nearly 3TB of redundant storage. But there is an inescapable truth: for most PC users, USB 3.0 has plenty of bandwidth for external storage.
Thunderbolt is one of those things that impresses easily but is difficult to recommend. There’s a lot to like about the technology, which squeezes multiple high-bandwidth protocols into a single cable just four millimeters in diameter. Seamlessly combining PCI Express and DisplayPort is a neat trick. Doing so while delivering 40Gbps of total bandwidth is the sort of thing Steve Jobs might have considered magical.
The real magic is what can be done with Thunderbolt. Take ultraportables, for example. They’re too thin to offer many expansion ports and often lack the chassis capacity and thermal headroom to accommodate lots of storage and powerful discrete GPUs. A single Thunderbolt hub could integrate all those things and provide connectivity for additional displays and more Thunderbolt devices.
In fact, Matrox has just announced a docking station that looks like a good first step in that direction. Unfortunately, you won’t find anything else like it among the Thunderbolt products currently being offered. External storage and specialized audio/video gear dominate the device list, and both appeal to niche markets. While plenty of users certainly need speedy external storage, the vast majority would be better served by USB 3.0 or even eSATA.
If the lack of compelling mainstream devices isn’t enough of an impediment, there’s also the cost. Thunderbolt is expensive to implement on motherboards and in notebooks. The associated cable is pricey, and it’s not bundled with devices. We’re still waiting for optical cables, too. A company called Sumitomo started sampling optical Thunderbolt cables in April, but there’s no word on retail availability or pricing. These optical cables aren’t designed to offer more bandwidth than the existing electrical ones; they’ll just allow for longer cable lengths.
Thunderbolt has plenty of potential for notebooks, where its utility is easy to understand. Since notebooks and mobile devices are a growing portion of the overall computing ecosystem, we expect Thunderbolt will play an important role going forward. Still, it’s difficult to see the appeal of Thunderbolt for desktop PCs not limited by chassis constraints. Modern desktops have I/O ports up the wazoo, and even integrated graphics solutions can power multiple digital displays simultaneously. The fact that Thunderbolt will likely be included only on high-end motherboards that already feature an abundance of PCI Express, Serial ATA, and USB 3.0 connectivity only makes it feel more redundant.