computers LAB 2.1 RESEARCH

Advantages OF MULTICORE PROCESSORS

The proximity of multiple CPU cores on the same die allows the cache coherency circuitry to operate at a much higher clock rate than is possible if the signals have to travel off-chip. Combining equivalent CPUs on a single die significantly improves the performance of cache snoop (alternative: Bus snooping) operations. Put simply, this means that signals between different CPUs travel shorter distances, and therefore those signals degrade less. These higher quality signals allow more data to be sent in a given time period since individual signals can be shorter and do not need to be repeated as often.

The largest boost in performance will likely be noticed in improved response time while running CPU-intensive processes, like antivirus scans, ripping/burning media (requiring file conversion), or searching for folders. For example, if the automatic virus scan initiates while a movie is being watched, the application running the movie is far less likely to be starved of processor power, as the antivirus program will be assigned to a different processor core than the one running the movie playback.

Assuming that the die can fit into the package, physically, the multi-core CPU designs require much less Printed Circuit Board (PCB) space than multi-chip SMP designs. Also, a dual-core processor uses slightly less power than two coupled single-core processors, principally because of the decreased power required to drive signals external to the chip. Furthermore, the cores share some circuitry, like the L2 cache and the interface to the front side bus (FSB). In terms of competing technologies for the available silicon die area, multi-core design can make use of proven CPU core library designs and produce a product with lower risk of design error than devising a new wider core design. Also, adding more cache suffers from diminishing returns.

DUAL CORE PROCESSOR ADVANTAGES
There are several advantages to having a dual core processor. The first advantage is that your computer will use less energy and deliver more total performance from both its cores than a single high performance chip design. The second is that dual core processor caches will perform better than a two chip design. You will also need less space requirements, since the die for the dual cores are printed on one chip. There is no need to create two separate chips, thus saving space. Another advantage is that the technology is very reliable and has been tried and tested

The FSB connects the MCH to the CPU (chipset) and the main memory and the L2 cache

■ Level 1: L1 cache is built in to the CPU and gives fast access to the most frequently used data. This level cache is the first one accessed by the CPU and is usually found in small amounts. However, it is the fastest cache to be found, offering the lowest latency of any of the types of cache. One of the reasons for this is that it resides within the CPU core. A typical Core i7 CPU might have 4 × 32 KB of L1 cache, 32 KB for each of its four cores. ■ Level 2: L2 cache is usually built on to the CPU (on-die) or on to each individual core. It is accessed after L1 cache, and it serves the CPU with less frequently used data in comparison to L1 but still more frequently used than DRAM data. L2 cache feeds the L1 cache, which in turn feeds the CPU. L2 is not as fast as L1 cache but is superior to DRAM sticks. This and L3 take up the majority of the CPU’s real estate. A typical Core i7 CPU might have 256 KB per core. ■ Level 3: L3 cache comes in the largest capacities of the three types of cache and has the most latency; therefore, it is the slowest. If the CPU can’t find what it needs in L1, it moves to L2 and finally to L3. Or you could think of it this way: L3 cache feeds L2 cache, which feeds L1 cache, which in turn feeds the CPU with data. If the CPU can’t find the data it is seeking, it moves on to the DRAM sticks. L3 cache could be on-die or onboard, but most of today’s CPUs have it on-die; however, it is shared among the cores of the CPU. A typical Core i7 CPU has between 4 and 8 MB of L3 cache.