What’s New?
WARNING: The following article contains some serious Geekspeak.
Intel’s new Core architecture was released late last year, and carries a price premium that kept them out of the mainstream. Now they have extended the series to the full range of consumer products
There is the i7, 900 series which was the first released and is sometimes referred to by the code name Bloomfield. The 900 series is quad core and carries 8MB of cache, and features Hyperthread® technology to simulate 8 cores. It also supports virtualization so it is capable of running all the latest software. The 900 series supports up to 24GB of RAM running on the Intel X58 chipset.
The X58 chipset motherboard is the significant other in this arrangement. It is a completely new technology that eliminates the Front Side Bus (FSB), and moves the memory controller to the processor. Instead of a Front Side Bus the X58 uses a QPI (Quick Path Interconnect), which is mind boggling in its complexity. To make it simple, just remember that Intel is giving us complex formula to figure the transfer rate, and the X58 is rated at 4.8 GT/s in a system where bigger numbers are better. There is a much more detailed explanation of the formula later in this article.
This month (September) they released the 800 series i7 (codename Lynnfield), running on a different chipset. The 800 series has many of the same features as the 900 series, at a lower bus speed, and of course at a lower cost. The 800 series runs on the Intel P55 chipset.
The P55 chipset supports dual channel memory and uses the new DMI (Direct Media Interface ) architecture. DMI chokes the PCIe bus down to 16 lanes, with SLi running at 8x8, but between the memory bus and the PCIe controller they have been able to bring down the cost of the P55 based motherboards.
While the biggest advantage of the 800 series is the price of the P55 based motherboards, the biggest advantage of the X58 based boards are their triple channel memory bus. On the X58 chipset memory is installed in threes, instead of in pairs like the P55 and all of the other recent chipsets available. This extra memory channel gives the X58 a significant boost in throughput over everything else out there, and the PCIe controller gives a full 40 lanes or 16x16 for SLi, with 4 “extra” lanes for a DMI link, and on some boards an extra 4x PCIe connection (Smokin’!).
The i5 (also Lynnfield) was also released this month and works off the same P55 chipset as the i7 800 series. The i5 is also Quad core but does not have Hyperthreading®. Again, there is a price advantage to the i5 series 700. Reports are that the i5 is significantly faster than the current Core 2 Quad (C2Q) 9650 processor, at a lower (chip) price. Of course the increased cost of the new motherboard and DDR3 RAM may offset any savings of the i5 over the C2Q processor based systems.
Both the i7 800series, and i5 700 series support up to 16GB of RAM, all Core processors utilize DDR3 RAM, at least all of them so far.
Intel promises to release the i3 series processors in coming months, but the specs for the i3 have not been generally released yet. However it is accepted that it will replace the much maligned Celeron Processor line.
Just a side note, Intel has also promised a 6 core i9 processor in 2010 (codenamed Westmere).
Let’s Get Technical:
Now, to understand what the manufacturers are telling you, you have to take the entire term and break it down. For example, the i7 920 processor lists its specs as 2.666GHz, 4.8GT/s QPI with 8MB cache and the i5 750 processor claims 2.66GHz, 2.5 GT/s DMI with 8MB cache.
GT/s = Gigatranfers per second. The PCIe bus which has taken the place of the old Front Side Bus requires that 2 extra bits be added to every byte in the encoding process, making a useful byte take up 10 bits. This presents a problem in communicating the speed of a system, since Gigabytes per second would reflect 25% more data than a Gigabyte of old.
This encoding process is called 8b/10b and adds two bits, and then strips the two bits away, leaving 8 bits of usable data. Since an encoded 10bit symbol only produces 8 bits of data, at least at an engineering level, the new designation seems appropriate.
So they came up with the Gigatranfers. The Gigatranfers per second (GT/s) is a measure of how many unencoded bits were transferred. It a measure of raw data.
Figuring Out The Chip Specs:
First we want to understand the relation between the numbers and letters. As I mention above 4.8GT/s means the CPU performs 4.8 gigatranfers per second. However you cannot relate the speed of the processor to the speed of the PCIe bus on which the GT/s rating is based. You see a 16 lane PCIe 2.0 bus can handle about 128 Gbps of raw data. It would seem a 4.8 GT/s is a pretty small piece of the 128 Gbps available, but actually it is very close to taking the entire data stream at full speed.
In the past all motherboards have used a “hub” based architecture, you may have heard the terms Northbridge and Southbridge referring to the matching chips that handle the data transfer across the motherboard. Those two chips were known as the “chipset”. Each piece of the chipset acts as a hub, to route data to the appropriate place in the system. The fastest chipset in the hub architecture transferred data at 12.8GBps
On this new QPI and DMI architecture, the Northbridge is eliminated and those duties are handled by the processor, including the memory bus.
QPI provides a wider PCIe bus at 20 lanes bidirectional (40 single lanes), where DMI has more standard 16 lane PCIe bus. Since the entire bus is built on PCIe standards now, the difference is significant.
When all the calculating is done, the QPI interface can transfer 25.6 GB/s which is exactly twice the rate of the fastest previous hub based motherboard. The DMI interface claims to handle 10GB/s although I was unable to confirm that specification on Intel’s website.
So the i7 is 2.66GHz clock speed, 4.8 GT/s per second, and uses the QPI interface which transfers up to 25.6 GB/s of data.
While the i5 has the same 2.66 GHz clock speed, it transfers 2.5 GT/s and the DMI interface can handle less than half the data across the motherboard.
Amazingly, the 2.66GHz 2.5GTs DMI i5 is considered noticeably faster then the top of the line Core 2 Quad 9650 which has 12MB cache, 3.0GHz clock speed and a 1333 bus speed (FSB).
