How Sandy Bridge Works

By: Jonathan Strickland

The Sandy Bridge Architecture

A silicon wafer of Sandy Bridge microchips, fresh off the manufacturing line.
A silicon wafer of Sandy Bridge microchips, fresh off the manufacturing line.
Courtesy Intel

Westmere, Sandy Bridge's predecessor, had an architecture based upon Nehalem. Sandy Bridge's architecture shares some similarities with the older chips but features a couple of major departures as well.

Sandy Bridge is a multicore microprocessor. That means each Sandy Bridge microprocessor has at least two processing cores capable of handling computational operations. At launch, the most advanced Sandy Bridge chip had four cores, making it a quad-core processor. But why use multiple cores at all? Why not just develop faster single-core processors?


It turns out that many computer processes are made up of smaller computational problems called parallel problems. Imagine a room that has a genius and four smart -- but not genius -- math students. You give the genius a sheet of four math problems to solve. You give each of the four smart students one of the math problems. While the genius might solve a single problem faster than any of the four smart students, collectively the students will finish before the genius. That's the idea behind multicore processors -- individually, they may be slower than a powerful single-core processor. But collectively, they're more efficient for lots of computer problems.

In addition to the multiple cores, each core itself can handle two threads of data. Intel included multithreading in the Nehalem microarchitecture and carried it over into Sandy Bridge. Intel now calls the technology Hyper-Threading. Multithreading depends heavily on software developers creating programs that can take advantage of the feature. With the right application, a single core can handle two threads of data, in effect doubling the processing power of the chip for those applications.

Each core in a Sandy Bridge chip has two levels of individual cache memory -- that means the cores can store some data within the processor itself to refer to while making computations. A third level of cache memory, called the last-level cache, is a shared resource. The cores refer to the last-level cache for shared data and to communicate with other cores.

The big departure for Sandy Bridge is the inclusion of a dedicated section on the chip for graphics processing. Out of the 995 million transistors on the Sandy Bridge quad-core desktop computer chip, 114 million of them reside in the graphics processing section [source: Lal Shimpi]. It can handle 3-D graphics processing. This capability decreases the necessity for a dedicated graphics card, though high-end applications like cutting-edge video games or video processing software may still require a graphics processing unit to run without a hitch.