Radeon HD5770 Detailed Features

The main attraction of ATI's new line of video cards is the brand new GPU with its 40nm transistors and an improved architecture. The chip in the 5700 series is called "Juniper" and is essentially half of the "Cypress", the high-end chip in the HD5800 series that was introduced in September, 2009.

The Juniper die is very small, as can be seen with this comparison to a well known dimensional standard. ATI still managed to cram over a billion transistors on there, and the small size is critical to the pricing strategy that ATI is pursuing with these new releases.

1 GB of GDDR5 memory, on a 128-bit bus with a 4.8 Gbps memory interface offers a maximum memory bandwidth of up to 76.8 GB/sec. Cutting the Cypress GPU in half limited the bus to 128-bit, but ATI has bumped up the clock rate on all their new boards. With GDDR5 running at 1200 MHz, the memory itself won't be a bottleneck on this card, but the narrower bus width does have a major performance impact. There is some room for memory overclocking via the Overdrive tool distributed by AMD.

The H5GQ1H24AFR-T2C chip from Hynix is rated for 5.0 Gbps, and is one of the higher rated chips in the series, as you can see in the table below. An overclock to the 1250-1300 MHz range is not unthinkable, especially if utilities become available to modify memory voltage.

The power section provides 3-phase power to the GPU; that's about average for a mid-range graphics card, and while increasing the number of power phases achieves better voltage regulation, improves efficiency, and reduces heat, ATI has used the inherently lower power requirements of the Juniper GPU and some fancy footwork in the power supply control chip to reduce power draw to very low levels.

Where the HD5800 series used a number of Volterra regulators and controllers, the HD5770 makes do with one L6788A controller chip from ST. It's still a relatively sophisticated controller, and the combination of a lower power GPU, low power GDDR5 memory, and smart power supply design yields an incredibly low power consumption of 18W at idle and 108W under duress. These numbers are derived from testing with 3DMark03; ATI says it pulls higher current than more recent versions of the synthetic benchmark. Another cost-cutting measure can be seen here, the use of standard electrolytic capacitors in a few locations.

Before we dive into the testing portion of the review, let's look at one of the most exciting new features available on every Radeon HD5xxx series product, Eyefinity.

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