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PCB Design

The Radeon HD 5970 seems to resemble the Radeon HD 5870, being a rectangular brick with a red stripe, but a PCB with two RV870 cores, two sets of high-speed GDDR5 memory, a PCI Express switch, and advanced voltage regulators just cannot be compact.

Indeed, the Radeon HD 5970 is 34 centimeters long while the Radeon HD 5870 and Radeon HD 4870 X2 are only 27 centimeters long. This device won’t fit into small system cases and is not actually meant for working in an HTPC or something. Its purpose is to serve in ultra-fast gaming stations which are usually assembled in roomy enclosures like the Chieftec Aegis, Cooler Master Stacker, SilverStone Temjin or Ante P193. The graphics card is rather heavy at 1.2 kilos, so we do not recommend using or moving a system with a Radeon HD 5970 without fastening its mounting plate to your system case. Otherwise, you risk damaging the card and the mainboard’s PCI Express slot.

The cooling system prevented us from seeing anything in the design of the device, so we hurried on to take it off. It was easy: we unfastened two screws on the mounting plate, some screws on the reverse side of the PCB, and removed the X-shaped springs that ensured proper contact between the graphics cores and the cooler’s heat-exchanger. Here is what we saw then:

The new card resembles its predecessor Radeon HD 4870 X2. Well, there are actually not many ways of placing a large PCI Express switch, two high-performance GPUs and memory on a single PCB and then powering everything up.

Judging by the amount of VT1157SF chips from Volterra, the total number of phases in the Radeon HD 5970’s power circuit is 10. The right GPU is powered by a 5-phase regulator while the left GPU (closer to the mounting bracket) is powered by a 3-phase regulator, but both regulators can be reinforced by installing one additional phase, transforming the 3+5 design into a 4+6 one.

The reinforced version may be used on Radeon HD 5970 cards with pre-overclocked frequencies or with a newer version of the RV870 chip (RV890?) with higher frequency potential. The memory chips are powered each from its own regulator which uses VT1157SF chips, too. There are as many as three Volterra VT1165MF controllers on the PCB to govern such a complex power subsystem. These controllers support flexible voltage adjustments by means of software tools.

There are a couple of connectors for additional power supply: a 6-pin PCIe 1.0 and an 8-pin PCIe 2.0 (by the way, both bonding pads allow installing 8-pin connectors). As usual, you can connect a 6-pin cable from your PSU to the card’s 8-pin connector. For the card to work then, you should close the two outermost pins of the connector or use an appropriate adapter that would trick the protection mechanism. This may be necessary, for example, with an Enermax Liberty ELT620AWT power supply which can power up any modern graphics card but is only equipped with 6-pin PCIe 1.0 connectors. We wouldn’t recommend doing this unless really necessary, though.

Hynix’s GDDR5 memory is installed on the PCB. The H5GQ1H24AFR-T2C marking indicates a capacity of 1Gb (32Mb x 32), a voltage of 1.5V and a rated frequency of 1250 (5000) MHz. We have seen such chips on Radeon HD 5770 and 5750 cards. Each GPU has a dedicated 1GB memory bank with 256-bit access consisting of eight chips, half of which are located on the reverse side of the PCB. Thus, the Radeon HD 5970 carries 16 GDDR5 chips with a total capacity of 2 gigabytes. 3D applications can only access 1 gigabyte because from a technical standpoint this graphics card is nothing but a Radeon HD 5870 CrossFireX tandem assembled on a single PCB.

As we have written in the previous section of this review, the memory frequency of the Radeon HD 5970 is lower than that of the Radeon HD 5870. It has been reduced from 1200 (4800) MHz to 1000 (4000) MHz. You should not worry about a lack of memory bandwidth. Due to the peculiarities of modern multi-GPU solutions the total memory bandwidth of the Radeon HD 5970 is as high as 256GBps, which is even higher than that of the GeForce GTX 295 with its two 448-bit memory buses but slower GDDR3 memory. The use of T2C-suffixed chips of GDDR5, rated for a frequency of 1250 (5000) MHz, and the advanced power circuit give us some hope for good overclocking.

The photo above shows a close-up of the Radeon HD 5970’s heart. It has three parts. Besides the two RV870 Cypress graphics cores, the PCI Express switch, marked as AMD8647, is highly important for its functioning. As a matter of fact, it is the same PLX Technology PEX8647 chip that used to be installed on the Radeon HD 4870 X2. It can intelligently switch 48 PCI Express 2.0 lanes and supports direct communication between the two graphics cores, so there is no need to replace such a good and time-tested solution with anything else. Interestingly, the support for an additional communication link between the GPUs known as Sideport which was declared but never activated in the Radeon HD 4870 X2 seems to be missing in the Radeon HD 5970 altogether. The RV870 just does not have the appropriate logic. Theoretically, an additional data channel with a bandwidth of 5GBps might provide some performance benefits but AMD must have carried out some tests and found those benefits not worth the trouble of implementing that channel. Of course, we don’t have any means to check this out by ourselves.

The GPUs were manufactured on the 38th week of 2009, i.e. between September 13 and 19. Both GPUs are full-featured RV870 working in maximum configuration with 1200 ALUs, 80 TMUs and 32 RBEs but their frequency is reduced in comparison with the Radeon HD 5870. The single-processor flagship of the new Radeon family has a core frequency of 850MHz but in the dual-processor card each core is clocked at only 725MHz, which must be necessary to keep the card’s heat dissipation within reasonable limits. Like with the memory frequency, this is no reason to worry. The two RV870, even clocked at a lower frequency, provide such a vast reserve of computing and texture-mapping resources that there is no older-generation solution to match them. Those 640 unified shader processors, 160 texture processors and 64 RBEs are impressive whatever the frequency. It is only if one GPU is idle that the new card is going to be slower than the Radeon HD 5870, but anyway faster than any modern single-processor graphics card.

Like a typical graphics card of the year 2009, the Radeon HD 5970 has two dual-link DVI-I ports with support for resolutions up to 2560x1600 inclusive and has a mini-DisplayPort in between. There is no HDMI connector as it could not be accommodated in the first row of the mounting plate. The second row is occupied by the exhaust hole of the cooling system. A dedicated HDMI connector is redundant, actually. You can easily get HDMI output by means of a DVI-D → HDMI adapter. Like other models in the fifth-generation Radeon HD, the Radeon HD 5970 supports three monitors simultaneously which theoretically allows using resolutions up to 7680x1600. But we guess that even two RV870 cores won’t be fast enough to ensure a comfortable frame rate at in a high display mode.

Like other members of the Radeon 5x00 and Radeon HD 4x00 series, the Radeon HD 5970 supports audio-over-HDMI thanks to a full-featured audio core integrated into the GPU. The audio core can output 8-channel sound in compressed (DTS, AC3) as well as uncompressed (LPCM) format including HD varieties such as DTS-HD and Dolby TrueHD.

Besides, the Radeon HD 5970 is equipped with a CrossFireX connector for building a 4-way graphics subsystem out of two such cards for a total of 6400 ALUs, 320 texture processors and 128 RBEs. This graphics subsystem will probably cope with the resolution of 7680x1600 pixels even in today’s most demanding games.

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