Multi-Core Technologies - HP DL585 - ProLiant - G2 Technology Brief

Multi-core technologies

In the past, the most common way to improve processor performance was to increase core
frequency and/or cache size. However, both of these solutions increase power consumption (and
heat generation) and have other limitations. Alternatively, higher performance can be achieved by
using multiple execution cores per processor. Multi-core processors run applications more efficiently
and allow multi-threaded software to achieve higher performance, while maintaining a similar
power budget to single-core processors. Also, multi-core processors are increasingly attractive with
reductions in the manufacturing process (for example, from 90 nm to 65 nm to 45 nm). This is
because smaller cores require less power, which permits more cores to be built into a single
processor.
AMD introduced its first dual-core AMD64 processor in 2005; it was manufactured using a 90 nm
process. The AMD Opteron processor is essentially divided into two parts: execution and
communications, with a system request interface and crossbar switch linking these two parts (see
Figure 2). The crossbar switch architecture enabled AMD Opteron processors to transition easily
from single-core to dual-core processors without fundamental design changes.
Each execution core includes a 64-KB/64-KB data/instruction L1 cache and a 1-MB L2 cache. The
system request interface manages and prioritizes the processor requests to the crossbar switch. The
crossbar switch connects both processor cores directly to communications: I/O (through
HyperTransport links) and the integrated memory controller. The memory controller and the
HyperTransport links remain the same as in a single core system.
Figure 2. The Socket F (1207) and Socket AM2 designs support dual-core AMD Revision F processors.
The primary difference between the processors designed for single, dual, or multi-core systems is in
the way the processor uses the HyperTransport link(s). In the 1000 series AMD Opteron processors,
the single HyperTransport link can only connect to I/O in a non-coherent link. This means that the
1000 series processors are limited to single-processor systems. In the 2000 series, one of three
HyperTransport links can connect to one other AMD Opteron processor in a coherent link. The
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