What makes the chipset tick
The chipset
Gaming potential
Taking a nod from the desktop counterpart, the mobile 780G packs in a considerable feature-set. Grafting what amounts to a DX10-compliant Radeon HD 2400 core into the northbridge, clocked in at the same 500MHz as the static variant, ATI/AMD actually delivers playable frame-rates in popular 3D game of today. We took a look at a pre-production AMD Puma system and compared its integrated-graphics' performance against an Intel Centrino (Santa Rosa refresh) right over here and found the Puma to be around 3x quicker.
Gamers would always be advised to look towards a laptop with a discrete card, of course, but the gap between IGP and low-end mobile discrete has closed sharply with the introduction of M780G.
The IGP's (integrated graphics) memory bandwidth, as you would expect, is taken from the system's, and that's why having a fast processor-to-chipset link - HyperTransport 3.0 - is important, because, as the block diagram shows, memory accesses have to traverse the Turion X2 Ultra CPU.
Just like the CPU, the HT 3.0 link can be speed- and voltage-modified, to save power when it's not required. Indeed, it can be entirely shut down when the application is executing solely on the CPU.
Lending a helping hand to high-definition decode
The 55nm northbridge adds 205m transistors - more than some discrete graphics-cards' - but has a thermal-design point (TDP) of around 3W when idling and 13W under load - comparable to M690G's. The chip also contains ATI's bandwidth-optimised UVD technology - a single-purpose portion of silicon which is designed to hardware-accelerate standard- and high-definition content that's encoded with H.264, VC-1, and MPEG2 codecs. In practical terms, that means Blu-ray and HD DVD content.
The idea, then, is to minimise CPU load and to extent battery-life, especially when Blu-ray drives become more prevalent in the mid-range space. AMD reckons it will be possible to play an entire Blu-ray movie, from a single charge, on a mid-sized laptop, based on reasonable settings and battery capacity.
DisplayCache - the cheap way of increasing performance and battery life
Manufacturers can choose to implement DisplayCache, which acts as a power-saving and performance-enhancing temporary store for display data. For example, if you have a static 2D screen that doesn't need refreshing, it becomes pointless to keep power-hungry HT links, CPU cores and system RAM wholly active.
With DisplayCache - previously known as SidePort - a 128MiB DDR2-800 memory can be physically positioned on board, interacting with the chipset through a narrow 16-bit bus, which, whilst not providing gobs of bandwidth, keeps the status quo with a lower power-draw.
DisplayCache, too, has another purpose. It can be combined with regular system memory and thereby used in an interleaved fashion - accesses from both pools of memory - by the chipset and CPU. Doing so, AMD reckons, can add around 10 per cent to the integrated graphics' gaming performance. We hope that laptop manufacturers take this feature on; it offers significant advantages for minimal extra cost.
Outputs galore
The desktop 780G supports an eclectic bunch of display outputs. The mobile variant does the same, providing the usual LVDS - for hooking-up to the screen - and VGA, to DVI, DisplayPort v1.1, and, strangely, only two-channel-supporting HDMI v1.2 (the spec. has provision for eight-channel sound). The triumvirate of digital outputs support HDCP-protected content. DVI and DisplayPort support resolutions up to 2,560x1,600 and HDMI v1.2 tops out at 1,920x1,200. We're a little surprised as to why ATI didn't implement higher-bandwidth HDMI v1.3 into the cutting-edge laptop, though.
One can drive two displays independently and concurrently, and you can run HDCP-protected content on both, at the same time. Interestingly, AMD reckons that DisplayPort will eventually replace LVDS as the conduit between chipset and laptop screen, freeing up a little more internal space.
PCI-Express
There are a total of 26 PCIe 2.0 lanes emanating from the northbridge. 16 can be used for laptops that ship with discrete graphics, usually via an MXM-based card, and the lanes can be toggled to 2x x8 for CrossFire multi-GPU purposes. A further six PCIe 2.0 lanes can be apportioned for general ASICs; gigabit networking being an example. The remaining four are used to connect to the SB700 southbridge.
Manufacturers are free to mix and match PCIe Gen 1.x and Gen 2.0 products as they see fit, too.
PowerXpress and Hybrid CrossFireX
ATI has a couple of nifty tricks up the M780G's sleeve. The first is PowerXpress, where, under Windows Vista, a laptop equipped with a discrete Mobility Radeon HD 3000-series GPU and M780G chipset, can be toggled from one form of graphics to the other (and vice-versa) without having to reboot the machine.
Why would you want to do this? The answer lies with conservation of the all-important battery life - why have a discrete card, albeit running in its lowest power state, taking precious voltage, when the power-efficient IGP is better-suited to the job of displaying bog-standard 2D images.
As HEXUS witnessed during the Puma tech day, the switching isn't seamless; it takes around five seconds to change from discrete to IGP - where drivers need to be unloaded and reloaded - and around 15 seconds the other way around. Still, it's better than a reboot, and we hope that AMD's partners make it a one-button option, rather than the user having to tinker with Catalyst Control Centre.
Hybrid CrossFireX also works in conjunction with the IGP and a discrete Mobility Radeon HD 3K GPU. Just like the desktop, the two DX10 cores, based on the same architecture, can be leveraged for additional performance gains - around 15 per cent higher than, say, a MR 3400's standalone scores.
The SB700
The southbridge is practically identical to the desktop version's, and that will come as no surprise. What's conspicuous and surprising by its absence, however, is the provision for HyperFlash - AMD's Robson-like technology - where NAND (memory) is placed on the motherboard and acts as a temporary storage buffer between chipset and hard drive(s) - that, the company says, hasn't gained sufficient traction for it to be a must-have feature.
The usual suspects are there, of course, including 14 USB 2.0 connections (how would you use them all?), six SATA2 ports, and HD Audio.
The SB700 isn't the leap ahead that 780G is. It's a southbridge that makes do, which is average rather than excellent, and feels like more of an afterthought than a grounds-up design.
Summary
The desktop 780G was strong in IGP-based gaming and multimedia, and that's why the M780G, which takes liberally and almost exclusively from that design, is good, too.
There's little to criticise here, and we're rather fond of justifiably criticising companies when products aren't up to scratch.
