sandy bridge

 

SANDY BRIDGE SPANS GENERATIONS

Intel Focuses on Graphics, Multimedia in New Processor Design

By Linley Gwennap  {9/27/10-01}

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Intel’s processor clock has tocked, delivering a nextgeneration architecture for PCs and servers. At the recent Intel Developer’s Forum (IDF), the company unveiled its Sandy Bridge processor architecture, the next tock in its tick-tock roadmap. The new CPU is an evolutionary improvement over its predecessor, Nehalem, tweaking the branch predictor, register renaming, and instruction decoding. These changes will slightly improve performance on traditional integer applications, but we may be reaching the point where the CPU microarchitecture is so efficient, few ways remain to improve performance. The big changes in Sandy Bridge target multimedia applications such as 3D graphics, image processing, and video processing. The chip is Intel’s first to integrate the graphics processing unit (GPU) on the processor itself.

periods. For notebook computers, these improvements can significantly extend battery life by completing tasks more quickly and allowing the system to revert to a sleep state. Integration Boosts Graphics Performance Intel had a false start with integrated graphics: the ill-fated Timna project, which was canceled in 2000. More recently, Nehalem-class processors known as Arrandale and Clarkdale “integrated” graphics into the processor, but these products actually used two chips in one package, as Figure 1 shows. By contrast, Sandy Bridge includes the GPU on the processor chip, providing several benefits. The GPU is now built in the same leading-edge manufacturing process as the CPU, rather than an older process, as in earlier products. This change alone provides a huge improvement

This integration not only eliminates an external chip, but it improves graphics performance by more closely coupling the GPU and the CPU. Sandy Bridge introduces the Advanced Vector Extensions (AVX), which double peak floating-point throughput. AVX will accelerate many 3D-graphics and imaging applications. The new processor also adds hard-wired video encoding.

Sandy Bridge will first appear in desktop and notebook processors that will be announced in early 2011 and branded as “2nd generation Intel Core” processors. It will later roll into a family of server processors. Because these chips use the same 32nm process as the current Westmere-based designs, increases in top speed will be modest. A focus on

power efficiency, however, enables Sandy Bridge to Figure 1. Arrandale versus Sandy Bridge. Arrandale combines a ^{achieve more performance within the same TDP} Westmere-based processor chip and a separate north-bridge chip in a limits as its predecessor. Improvements in turbo single package. Sandy Bridge combines the processor and the north mode enable even greater performance for short time bridge, including graphics, on a single chip.

SEPTEMBER 2010

in performance per watt, increasing the speed
of the shader engines while reducing their power.

The GPU can now access the processor’s large levelthree (L3)
cache (which Intel now calls the last-level cache, or LLC). When graphics
functions executed in a simple pipeline, caching was irrelevant. A modern
shader-based architecture, however, can access the same data over and over as
it layers one effect over another. The L3 cache short-circuits the path to main
memory, providing its information much more quickly. This extra speed improves
graphics performance while reducing pressure on the limited DRAM bandwidth.

Instead of carrying forward a GPU from an earlier chipset,
Intel’s graphics team in Folsom, California, totally redesigned the Sandy Bridge
GPU. The biggest change is the amount of fixed-function logic. Although
programmable shaders (which Intel calls execution units, or EUs) are area
efficient, performing many different graphics functions in a single unit,
fixed-function blocks are more power efficient for any given task. Taking
advantage of the 32nm technology’s greater transistor budget, Intel added more
fixed-function units for common tasks such as texturing, vertex processing,
rasterization, and Z-buffering. This approach, which is widely used by other
GPU vendors, allows the shaders to focus on shading; they also perform unusual
tasks that are not worth implementing in dedicated hardware.

Intel also redesigned the shaders themselves. Because these
units have a proprietary instruction set, the company can make radical changes
to the architecture as long as it rewrites its drivers to compensate. For Sandy
Bridge, Intel expanded the shader’s register set, improved the parallel
branching, and added a transcendental math (e.g., sine and cosine) unit to
speed up those functions. Each shader is multithreaded and can execute two
instructions per cycle. The new GPU has up to 12 shader engines that operate at
one-third of the CPU frequency. Each shader can generate eight single-precision
floating-point operations per cycle, producing total GPU performance of 96 FP
operations per GPU clock cycle, or 109 gigaflops at a CPU speed of 3.4GHz. By
comparison, the shaders in Nvidia’s high-end GeForce GTX 480 GPU are rated at a
total of 1,345 gigaflops, albeit at a much higher price and power level.

As Figure 2 shows, the GPU also contains a multiformat codec
engine (MFX) that performs video decoding for MPEG2, VC1, and H.264 AVC at up
to 1080p (HD) resolution. Although current platforms also have a videodecoding
engine, this unit does not perform motion compensation and in-loop deblocking;
these critical functions are dumped on the programmable shaders, resulting in
greater power consumption. Like most competing hardware video decoders, Sandy
Bridge’s MFX performs the entire decode process in hardware, cutting power in
half compared with the previous platform.

Unlike current platforms, Sandy Bridge also performs hardware
video encoding. The encoder handles the H.264 AVC and MPEG2 codecs, again at
1080p resolution. Other codecs are encoded in software on the main CPU.
Shifting video encoding to the GPU’s media engine not only greatly reduces
power but also improves performance. This speedup is important during video
transcoding (converting from one codec to another), which can be processed
faster than real-time video capture. Using the new hardware engine, Sandy
Bridge can encode AVC video much faster than current platforms; Intel did not
disclose how fast, but it claimed at IDF that “tasks that once took minutes
will now take seconds.”

AVX Widens FPU to 256 Bits

As announced by Intel in 2008, AVX is a new
set of x86 instruction-set extensions that logically follows SSE4. AVX
increases the width of the 16 XMM registers from 128 bits to 256 bits; the
wider registers have the tasty moniker YMM. Each register can hold eight
single-precision (SP) floating-point values or four double-precision (DP)
floating-point values that can be operated on in parallel using

Figure 2. Sandy Bridge graphics unit. The GPU contains a number of
programmable shaders (EUs) that are assisted by several fixed-function blocks
that perform common graphics and video tasks.

SIMD (single-instruction, multiple-data)
instructions. AVX also adds three-register instructions (e.g., c=a+b), whereas
previous instructions could only use two registers (a=a+b).

To implement the AVX instructions, Intel extended the width
of the FP multiply unit and the FP add unit to accommodate the wider YMM
registers. To save die area (and thus leakage current), instead of just adding
more FP transistors, the lower half of the calculation uses the existing
128-bit SIMD integer data path. Of course, this approach still adds some new
transistors to implement the new capability, but it adds fewer than separate
units would require.

The new FPU has a 256-bit FP multiply (FMUL) unit and a
separate 256-bit FP add (FADD) unit. Together, these two units can perform 16
SP operations per cycle. AMD’s Bulldozer CPU (see MPR
8/30/10-01,“AMD
Bulldozer Plows New Ground”) achieves the same level of peak performance in a
different way: it provides two 128bit FP multiply-add (FMA) units that can be
combined to execute one 256-bit FMAC instruction per cycle. Sandy Bridge does
not implement FMA (which will likely debut in the 2013 Haswell CPU), but it can
achieve its peak performance on code that uses separate FADD and FMUL
instructions. Note that Bulldozer’s peak performance is cut in half when using
FADD and FMUL instead of FMA.

Register Files Get Physical

To produce the Sandy Bridge CPU in just two
years, Intel’s Haifa (Israel) team borrowed heavily from the Nehalem CPU
design, following the principle of “if it ain’t broke, don’t fix it.”
Implementing AVX, however, broke the register-renaming method used in Nehalem
(and its predecessor, Merom, which was also designed by the Haifa team). In
these previous CPUs, each instruction stores its source values in the scheduler
and its result in the reorder buffer (ROB), which copies the result to the
physical register file once the instruction is retired. In-flight instructions
must check the ROB (using a content-addressable memory) to locate the most
recent copy of any source registers that they require.

Implementing AVX doubles the potential operand size, which
could greatly increase the size of both the scheduler and the ROB. Instead,
Intel decided to revert to the physical-register scheme used in the old Pentium
4 (and by most RISC processors that implement register renaming). In this
method, the CPU implements a rename register file that is much larger than the
logical register file. When an instruction is issued, its result is assigned to
an unused entry in the rename file. Its source operands are taken from the appropriate
rename registers defined by the current mapping. If an exception occurs, the
CPU simply replaces the register map with the most recent committed mapping.

This approach eliminates the copying of data from the ROB to
the physical register file, saving power. The rename entries for each register
file are the same width as that file, so only the YMM rename registers need to
be 256 bits wide; using the previous method, every entry in the scheduler and
the ROB would have to be able to hold a 256-bit result. As Table 1 shows, this
simplification also enabled the team to increase the number of scheduler and
ROB entries by 50% and 30%, respectively, increasing the size of the reorder
window.

Branch Predictors Get Small

The Sandy Bridge team focused on a few other
areas to improve the CPU. Because of Nehalem’s long pipeline, accurate branch
prediction is critical to its performance. Mispredicted branches not only waste
many CPU cycles, they also waste the power used to execute the unneeded
instructions. The team wanted to improve the accuracy of the branch predictor,
but without taking a brute-force approach that required more memory and thus
more power.

To do so, the team discarded the long-standing wisdom that a
2-bit predictor is better than a 1-bit predictor. Most branches are, in fact,
monotonic, so the 2-bit predictor provides a relatively small improvement in
accuracy—not enough, the team reasoned, to justify the cost and power of the
second bit. Put another way, a 2-bit predictor is less accurate than a 1-bit
predictor with twice as many entries, yet both use about the same die area and
power. Sandy Bridge actually implements slightly more than 1 bit per entry,
sharing a single “confidence” bit across several entries to save space and
power.

The team then looked at the branch target buffer (BTB), which
used 64-bit entries to hold the target addresses. Most branches, however, have
very short displacements, looping back or jumping forward several instructions
or so. The Sandy Bridge BTB has mostly small entries to hold these offsets,
with a few wide entries for long-displacement branches. This change saved so
much space that the team was able to double the number of BTB entries and still
have room left over. This extra space is used to extend the global branch
history, further improving prediction accuracy. As a result, accuracy is
improved within about the same die area and power for the branchprediction
unit.

Like Nehalem, Only Better

Like Nehalem, Sandy Bridge uses a 32KB
instruction cache and decodes four x86 instructions per cycle, converting them
into simpler RISC-like micro-ops. A new addition is the micro-op (L0) cache,
which can hold 1.5K micro-ops. Assuming an average of 3.5 bytes per x86
instruction, this cache is the equivalent of a 5.25KB instruction cache. Intel
claims that the typical hit rate for this cache is about 80%. The L0 cache
replaces Nehalem’s loop buffer, which also stores micro-ops but has only 28
entries.

Because instructions already stream from the instruction
cache at the pipeline’s full rate, the new design saves cycles only when
execution can be restarted from the L0 cache after a mispredicted branch. The
overall perform-

	Nehalem	Sandy Bridge
Load Buffers	48 entries	64 entries
Store Buffers	32 entries	36 entries
Scheduler Entries	36 micro-ops	54 micro-ops
Integer Rename File	Not applicable	160 registers
FP Rename File	Not applicable	144 registers
Reorder Buffer	128 micro-ops	168 micro-ops

Table 1. Nehalem versus Sandy Bridge. The new CPU design replaces
the old physical register file, which contained a single copy of each logical
register, with a new larger set of rename registers. Sandy Bridge also expands
the size of the reorder buffer, the scheduler, and the load and store buffers,
providing the CPU with greater opportunities to reorder instructions. (Source:
Intel)

ance improvement is thus minimal. More
importantly, instructions whose micro-ops are already in the L0 cache do not
need to be fetched, predecoded, decoded, and converted to micro-ops. Thus, the
new cache reduces the power used for these complex tasks by about 80%.

Aside from the AVX changes, Sandy Bridge uses the same
execution core as Nehalem. Its 32KB data cache is backed by a 256KB level-two
(L2) cache, as Figure 3 shows. Nehalem’s data cache, however, supports one
128-bit load and one 128-bit store per cycle. Sandy Bridge can perform two
loads and one store per cycle, doubling the load bandwidth. This change helps
support the AVX instructions, enabling the cache to perform one 256-bit AVX
load per cycle. AVX stores require two cycles to complete.

Ring Around the Cores

Sandy Bridge contains a new component, the
system agent, that controls what was previously called the north bridge: the
memory controller, PCI Express, display interfaces, and the DMI connection to
the external south-bridge chip (PCH). The exact system interfaces will vary
depending on the target platform, but the initial products will support two
DDR3 SDRAM channels and a single ×16
PCI Express 2.0 interface that can also be configured as two ×8 ports. The chip uses the
Embedded DisplayPort interface to connect to the internal display in a notebook
computer. Other display and system interfaces are in the south bridge.

Instead of the single L3 cache used in Nehalem and Westmere,
Sandy Bridge divides the L3 cache into four blocks. Intel has not disclosed
details, but we expect each block to be 2MB in size, totaling 8MB of L3 cache
in a four-CPU processor. Although each CPU is physically adjacent to one of the
cache blocks, there is no association of data between the CPU and its
neighboring cache block. Instead, each CPU simply sees a single, large L3
cache. Dividing this cache into four blocks, however, allows each block to
service requests simultaneously, quadrupling the total cache bandwidth. At
3.4GHz, the L3 cache can deliver 435GB/s.

To improve bus bandwidth and simplify scalability, Sandy
Bridge implements a ring interconnect instead of the usual internal bus. Intel
used a ring in Nehalem-EX and in its ill-fated Larrabee (seeMPR
9/29/08-01,“Intel’s
Larrabee Redefines GPUs”), but it has not previously used this structure in its
mainstream processors. Other processors use rings—notably, NetLogic’s XLR and
XLP (see MPR
7/26/10-01,“NetLogic
Broadens XLP Family”).

Because each station in the ring connects only to the next
station, the ring segments are short enough to operate at the full CPU speed.
Furthermore, each ring segment can potentially carry different data. (The Sandy
Bridge design actually includes four separate rings: one for data and three for
address, coherency, and control information.) The downside of a ring is that
data may need to traverse multiple hops to get to its destination. These extra
hops add latency, but given the faster speed of the ring, two or even three
hops can take as little time as a single transfer on a traditional multidrop bus.

Figure 3. Complete block diagram of Sandy Bridge CPU. Important
changes from Nehalem include an improved branch predictor, a new micro-op
cache, new AVX registers and execution units, and the ability to load two 128-bit
values per cycle from the data cache.

Sandy Bridge implements a unique type of ring that minimizes
the number of hops. As Figure 4 shows, the ring has 10 stations, but each
CPU/cache block shares two stations, one connected to the portion of the ring going
“up” and the other connected to the portion going “down.” For each transfer,
the ring interface chooses the direction, up or down, that will get the data to
its destination the soonest. In this configuration, the worst-case number of
hops to or from any CPU or cache is four. Because a CPU can access its
associated cache block without using the ring (i.e., zero hops), the average
trip from a CPU to cache is only 1.25 hops. The average trip from a CPU/cache
to or from the GPU or the system agent is 2.5 hops. As a result, the average L3
cache latency is 26 to 31 cycles compared with about 36 in Nehalem.

Assuming that 25% of the cache traffic passes directly
through to its neighboring CPU without getting on the ring, the ring itself
must handle three transactions per cycle to sustain the remaining cache
bandwidth. That means, on average, either the up or down leg must handle two
transactions at once, which may be difficult to schedule. Thus, the ring may
not be able to sustain the full bandwidth of the caches, but it will provide
much greater bandwidth than Nehalem’s internal bus.

The architecture easily scales downward by removing two of
the CPUs and their associated cache blocks. This change reduces both the size
and bandwidth of the L3 cache to match the reduction in CPU count. With only
two cache blocks, the ring can sustain the full cache bandwidth. Alternatively,
the architecture can be extended to eight or more CPUs. In this case, Intel
could double the ring width to 512 bits to help support the greater bandwidth
of the additional cache blocks.

Figure 5 shows a die photo of the chip in which the six ring
stations can clearly be seen. Intel did not disclose the die size of the chip,
but it is said to be about 225mm². The graphics and video unit at
the bottom of the chip takes 20% of the total die area. This unit appears to
consist mainly of synthesized logic, whereas the CPUs and caches use custom
circuit design to maximize performance. The north-bridge logic, not counting
the I/O drivers, is only 8% of the die. The four CPUs together use 33% of the
die, making them just under 20mm² each. The 8MB of L3 cache (L3$)
covers 20% of the die. Most of the I/O drivers are for the two 64-bit channels
of DDR3 SDRAM. Note that removing two of the CPUs and two of the cache blocks
would reduce the total die area by about 30%.

Revving Up Turbo Mode

As with Intel’s other multicore processors,
the frequency of each CPU core can be adjusted individually, so it can be

turned on or off as needed. Even when its
clock is turned off, however, the CPU burns leakage power. So, when the
processor is truly idle, the voltage to the CPUs can be turned off, completely
eliminating their power dissipation. The graphics unit is on a separate voltage
plane, so it can be disabled for applications that do not require graphics. The
system agent and north-bridge logic are on a third power plane, which allows
the north bridge to refresh the display while the rest of the processor is
asleep.

The system agent contains the power manager—a programmable
microcontroller that controls the power state of all units and controls reset
functions. This approach allows power-management decisions to be made more
quickly than by running a driver on one of the CPUs.

If only one Nehalem CPU is active, it is allowed to exceed
its rated speed, since even at a higher speed, one CPU will not exceed the
multicore chip’s total TDP budget. Intel calls this feature turbo boost. Sandy
Bridge takes a different view of turbo boost, focusing on die temperature
rather than instantaneous power dissipation.

Consider a processor that has been sitting idle for several
seconds; perhaps the user is considering what digital effect to apply to a
photograph. The processor and its thermal system (e.g., heat sink) will cool
down. If the user

Figure 4. High-level block diagram of Sandy Bridge. The L3
cache is divided into four blocks, which are connected to the four CPU cores,
the GPU, and the system agent through a ring interconnect.

Figure 5. Sandy Bridge die photo with overlay. The red
boxes show the ring stations. The 12 shaders (EUs) can be seen at the lower
left. (Source: photo by Intel, overlay by The

Linley
Group)

then begins a CPU-intensive activity, the
entire processor can operate well above its rated TDP for quite some time (up
to 25 seconds, Intel claims) while the thermal system heats back up. Once the
chip reaches its maximum operating temperature, it must throttle back to its
rated TDP level to avoid overheating.

Sandy Bridge’s power manager estimates the chip’s temperature
and calculates the degree and duration of the turbo boost. In this design, the
maximum CPU speed in turbo mode is limited only by the physical speed of the
transistors and the current that can be supplied to the chip. Turbo mode should
be particularly effective in mobile Sandy Bridge chips, since these chips have
more headroom. Because the chip does not physically measure its own
temperature, the power manager estimates the temperature on the basis of recent
workloads and the thermal characteristics of the device and its cooling system.
Presumably, Intel has built in a safety factor, but any unauthorized or even
unintentional modification of the cooling system could wreak havoc with the
power manager’s calculations.

The integration of GPU and CPUs on one chip creates additional
turbo opportunities. If the GPU is not in use or is operating at a low speed,
the power manager can assign some of its thermal budget to the CPUs, allowing
them to run at a higher clock speed. Conversely, on a graphics-intensive
application, the power manager can overclock the GPU while slowing down the
CPUs.

Turbo mode should provide a noticeable speedup to PC users—up
to 40% in some situations. Users who often leave their system idle or in a
low-power state before launching a brief burst of computation will particularly
benefit. Gamers or professional users who execute long CPU-intensive jobs will
not see as much gain. Benchmarking a Sandy Bridge processor could generate
widely different results depending on how the test is run. Intel recommends allowing
the processor to rest quietly for a moment before running each benchmark, but
this approach may not be indicative of real-world usage.

Sandy Bridge Transition in 2011

As with previous generations, Sandy Bridge
will sweep through Intel’s entire product line, but the transition will take
some time. The initial products, which are due to appear early next year, will
be in the Core i3, Core i5, and Core i7 product lines. Although Intel has not
announced details, leaked roadmap slides provide the initial product
configurations. According to this information, these products will offer two or
four CPUs at speeds of up to 3.4GHz. The high-end 3.4GHz four-core version will
top out at 95W TDP. Mobile versions with four cores at 2.5GHz will use 55W TDP,
with a dual-core 2.7GHz version rated at just 35W TDP. Some models (probably
the dual-CPU versions) will use 6 shaders instead of 12, reducing graphics
performance.

Together, these Sandy Bridge products will quickly displace
the dual-core Arrandale (mobile) and Clarkdale (desktop) processors, as Figure
6 shows. Some high-end PCs are still using the quad-core Clarksfield (mobile)
and Lynnfield (desktop) processors, which are built in 45nm technology; these
products can convert to the quad-core Sandy Bridge processors.

Sandy Bridge will cross into the server market in 2H11 using
a platform called Romley. At IDF, Intel demonstrated Romley-EP, a dual-socket
(2P) platform that succeeds Tylersburg-EP, using a version of Sandy Bridge with
eight CPUs. An eight-CPU version uses more die area than the six-CPU Westmere
chip, but Sandy Bridge’s lower power per CPU should allow it to fit into a
similar thermal budget (TDP).

For 4P and 8P systems, Intel is preparing the RomleyEX
platform, which follows Westmere-EX (see MPR
9/20/10-01,“Intel
Unveils Atom E6xx, Westmere-EX”) and the Boxboro-EX platform. The new high-end
platform

Figure 6. Intel processor roadmap. In early 2011, PC users will
convert from Intel’s Arrandale and Clarkdale processors to Sandy Bridge. In
2H11, servers will convert to the Romley platform, which supports new versions
of Sandy Bridge.

includes the Sandy Bridge-EX processor, which
we expect to have 12 CPUs.

Intel has disclosed little about Romley but says it will use
a new version of Intel’s Quick Path Interconnect (QPI) to connect the
processors to each other. Sandy Bridge-EP will include two QPI v1.1 links for
this purpose. Intel has not specified the speed of the new version, but QPI
v1.0 delivers 12.8GB/s in each direction at a clock rate of 3.2GHz. We expect
the new links provide a modest increase, perhaps to 3.8GHz. The processor will
still use DMI to connect to the south bridge, which in the Romley platform is
code-named Patsburg.

We expect the server versions of Sandy Bridge to have some
minor changes in addition to the greater number of CPUs. The on-die graphics
unit will probably be omitted. Whereas Westmere-EP has three DRAM channels for
six CPUs, Sandy Bridge-EP could use four channels to provide a better match for
its eight CPUs. Although the initial Sandy Bridge processors will integrate PCI
Express 2.0, the server versions provide a good opportunity for Intel to debut
the faster PCI Express 3.0. The new specification, which is due to be completed
in late 2010, doubles PCI Express throughput to 8Gbps per lane, or 16GB/s for a
16lane slot.

Intel has already taped out its first 22nm processor.
Following the tick-tock plan, Ivy Bridge is a 22nm shrink of Sandy Bridge that
is scheduled to enter production in late 2011. As a “tick,” Ivy Bridge is not
expected to add many new features to the platform, but the 22nm process will
significantly reduce power per CPU and enable Intel to put more CPUs on a chip.
Following Ivy Bridge is Haswell, the next tock. Little is known about Haswell,
but it is said to be a completely new CPU microarchitecture.

Intel Steamrolls Bulldozer

AMD “coincidentally” disclosed its
next-generation Bulldozer architecture just one month before Intel disclosed
Sandy Bridge. Thus, it is natural to compare the two designs. Although AMD has
beefed up its microarchitecture, Bulldozer matches up better against
Nehalem/Westmere than it does against Sandy Bridge, as Table 2 shows. Intel has
again upped the ante by expanding the reorder capabilities of its CPU. Sandy
Bridge’s micro-op cache is a unique feature that offers performance and
power-savings opportunities. We also suspect Intel’s branch prediction is
superior, although neither vendor has disclosed enough information to be sure.
Bulldozer’s 16KB data cache may also hinder it on certain single-thread
applications.

On dual-threaded applications, Bulldozer’s unique two-core
module offers clear benefits over Intel’s HyperThreading design. Sandy Bridge
must share its execution units and reorder buffer between the two threads,
whereas

Bulldozer offers each thread a separate set
of resources. But

	AMD Bulldozer	Intel  Westmere	Intel  Sandy Bridge
Building Block	Dual CPU	CPU core	CPU core
Integrated Graphics?	Not disclosed	In package	On chip
Instruction Extensions	SSE1–SSE4.2,  AES, AVX	SSE1–SSE4.2,  AES	SSE1–SSE4.2,  AES, AVX
Number of Threads	2 threads	2 threads	2 threads
Instr Decode Rate	4 per cycle	4 per cycle	4 per cycle
Micro-Op Issue Rate	4 per cycle*	4 per cycle	4 per cycle
Instr Reordering	128 micro-ops*	128 micro-ops	168 micro-ops
FP Operations (SP)	16 per cycle	8 per cycle	16 per cycle
L0 (micro-op) Cache	None	None	1.5K micro-ops
L1 Cache (I/D)	64KB/16KB†	32KB/32KB	32KB/32KB
L2 Cache	Undisclosed	256KB	256KB
IC Process	32nm	32nm	32nm
First Production	Mid-2011‡	Early 2010	Early 2011

AMD counts each Bulldozer module as two
cores, so all we can say is that two Bulldozer

Bulldozer is headed straight for the server
market in the Valencia and Interlagos processors. Thus, Bulldozer may actually
appear in servers before Sandy Bridge does (in the Romley platform).

Whereas Sandy Bridge is the clear winner on a coreto-core
basis, a Bulldozer core will use much less power, allowing AMD to operate
Valencia at a higher clock speed within the same thermal envelope. Sandy
Bridge-EP should handily outperform Valencia on SPECint per watt, although the
Bulldozer chip may narrow the gap from current products.

Rising to the Next Level

Sandy Bridge brings several architectural
innovations to Intel’s platforms. PC users will see the biggest improvements in
multimedia performance, particularly video encoding but also graphics and image
processing. On these types of applications, which are becoming increasingly
popular, users will see an improvement of 2×
or better compared with Intel’s previous graphics solutions.

The CPU microarchitecture improvements are fairly subtle,
given the evolutionary design approach. We expect performance per megahertz to
improve very modestly, perhaps by 10% on most applications. Many of the design
changes, particularly the L0 micro-op cache, aim to reduce power more than to
increase performance. Intel has not quantified these gains, but we estimate
they could trim CPU power by 10% at the same clock speed. Because most of the
company’s products are power limited, Intel can turn power efficiency into
higher clock speeds at the same TDP levels, providing an effective performance
boost of 20% for Sandy Bridge compared with Westmere. In certain situations,
the improved turbo boost will magnify this gain by as much as 40%, which can
translate directly into longer battery life for notebook computers.

cores are better than one Sandy Bridge.

Although AMD has been talking about integrating graphics for
years, Intel has actually been doing it, first with the two-chip module of
Arrandale and Clarkdale and then with the single-die Sandy Bridge. AMD’s first
Fusion chip, code-named Ontario (see MPR
8/30/10-02,“Bobcat
Snarls at Atom”), is scheduled to debut in 4Q10, only slightly before Sandy
Bridge. We do not expect the first Bulldozer processors to integrate graphics.
Sandy Bridge should negate any gains AMD might have achieved from its Fusion
project.

Sandy Bridge products will appear in early 2011, whereas we
expect the first Bulldozer products to ship in mid-2011. Although this schedule
gives Sandy Bridge a head start of several months in the desktop and mobile
markets,

Table 2. Comparison of AMD Bulldozer and Intel Sandy Bridge CPUs. Greater
instruction reordering and an L0 cache should improve Sandy Bridge’s
performance over Bulldozer’s. *Dedicated amount for each thread; †L1 data cache
dedicated for each thread. (Source: vendors, except ‡The Linley Group estimate)

For
More Information

Intel has
not yet announced any products using the Sandy Bridge architecture. We expect
the first Sandy Bridge products to ship in early 2011. For more information on
Sandy Bridge, download Intel’s IDF presentations fromwww.intel.com/go/idfsessions(search for Sandy Bridge). For
complete information on the AVX extensions, accesshttp://software.intel.com/en-us/avx.

The integration of graphics has several effects. It increases
performance while greatly reducing power: we expect a performance gain of about
2× at one-fifth
the power compared with the Arrandale/Clarkdale graphics unit. Integration is
likely to reduce manufacturing cost compared with the current two-chip module
(or with an external GPU chip). Graphics integration also makes PC makers less
likely to choose a third-party graphics solution. Although the performance of
Intel’s graphics has generally been modest at best, the improvement in Sandy
Bridge makes it acceptable for most PC users. Gamers and others who care about
maximizing graphics performance will still opt for an external graphics card.

Intel’s rollout schedule brings Sandy Bridge to the PC market
in early 2011, but it will not reach the server market until late that year. In
targeting the PC market first, Intel satisfies the bulk of its customer base
and should extend its lead over AMD in PCs. But AMD’s focus on the server
market may allow Bulldozer to beat Sandy Bridge to that market. Furthermore,
AMD’s strategy of making Bulldozer a smaller, lighter core may prove more power
efficient than Intel’s bulkier Sandy Bridge. AMD has been successful with server
customers by undercutting Intel on price; Bulldozer may provide it with an
additional advantage in that market.

Intel’s track record of bringing new processor architectures
to market is impressive and unrivaled. No other processor vendor can completely
remake its product line on an annual basis, yet Intel has done just that in
each of the past four years. With Sandy Bridge, the company is poised to go
five for five. The new processor shows that Intel is thinking outside of the
CPU box, delivering new graphics and multimedia capabilities to support
emerging usage models. Taking advantage of the growing transistor budget
provided by its industry-leading fab technology, the company is integrating new
features along with additional system functions, improving efficiency. Sandy
Bridge will

carry Intel into the next generation of PCs. ♦

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