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PCB Design and Functionality

The Palit Radeon HD 4870 Sonic 1024MB is designed in a unique way. Let’s take a look at it.

So, this is surely not the reference cooling system. I will discuss it in detail shortly. Note that this is a dual-slot cooler, too. It has become quite normal already for a modern graphics card to occupy two expansion slots.

The PCB has become 14mm shorter and 4mm thicker than the reference Radeon HD 4870 and now measures 230x99x39mm. The reduced length of the card should be appreciated by its users because many top-end cards are just too long to fit into small system cases.

The card’s mounting bracket has an original design, too. It carries analog and DVI video outputs, HDMI and DisplayPort interfaces, and a small switch for changing the card’s operation mode from Normal to Turbo and back again.

There is also a vent grid for exhausting the hot air out of the system case even though the cooler’s fans are oriented towards the mainboard rather than in parallel to it as in the reference cooler.

The cooler’s plastic casing can be removed easily. Now we can take a look at the cooler’s heatsink and the face side of the card’s PCB.

The heatsink is fastened with four screws to an X-shaped backplate you can remove easily.

The four-phase voltage regulator looks like this:

The power circuit differs considerably from the reference Radeon HD 4870 although the two 6-pin power connectors have been left in their places (but they are oriented upward here). The Radeon HD 4870 specifications declare a peak power draw of 170 watts, so a 500W power supply is recommended for a computer with such a card. A 600W or higher PSU is recommended for a CrossFire configuration.

A small aluminum heatsink is installed via a thin thermal pad on the card’s power components.

There was a surprisingly thin layer of gray and thick thermal grease on the GPU. I removed it to examine the latter.

So, this sample of Palit Radeon HD 4870 Sonic employs a 55nm RV770 processor manufactured in Taiwan on the 32nd week of this year. The GPU has 800 unified shader processors, 40 texture processors and 16 render back-ends. Now, when the switch on the card’s mounting bracket is set at Normal, the GPU frequency is 750MHz in 3D mode, which matches the Radeon HD 4870 specs. But when you set the switch at Turbo and reboot your computer, the GPU frequency grows up to 775MHz. That’s a small but nice bonus. The GPU frequency is reduced to 500MHz in 2D mode, irrespective of the position of the switch, to save power and lower the temperature of the graphics core.

The key difference of the Palit Radeon HD 4870 Sonic from the reference card and competitor’s versions is that it has twice the standard amount of memory. Its 1024 gigabytes of memory are provided by eight GDDR5 chips from Qimonda manufactured on the 34th week of 2008.

These Revision A1 chips are marked as IDGV1G-05A1F1C-40X. The specified access time is 1 nanosecond. The theoretical effective clock rate is 4000MHz. As opposed to the reference Radeon HD 4870, the memory frequency is 3800MHz in the Normal mode (200MHz higher than on the reference card) and grows up to 4000MHz in the Turbo mode (+400MHz). Again, you have to reboot your system after you change the operation mode (this is necessary for the card to switch to another BIOS).

The following screenshot shows the card’s characteristics in the Turbo mode:

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