Intel is launching this month their new CPUs based on the “Sandy Bridge” architecture. Let’s check the performance of the new Core i5-2500K (3.3 GHz) and compare it to its main competitor from AMD, the new Phenom II X4 975 Black Edition (3.6 GHz) that is being released today. We also added the Core i5-661 in the mix.

For a detailed explanation of what is new in the Sandy Bridge architecture, please read our Inside the Intel Sandy Bridge Microarchitecture tutorial.

The new Core i5 2500K (3.3 GHz) is a quad-core CPU, coming in two flavors: with its clock multiplier unlocked (“K,” being the equivalent to the “Extreme Edition” CPUs Intel used to carry and to the “Black Edition” CPUs from AMD), giving you an extra way to overclock the CPU, and the standard model with a locked clock multiplier. The “K” model comes with a price tag of USD 216, while the standard model comes priced at USD 205.

The new quad-core Phenom II X4 975 Black Edition comes with a price tag of USD 195.99, being the main competitor to the Core i5-2500, and in this review we will be able to answer the most basic question of all: which one is the fastest?

We also included in our review the Core i5-661, which runs at almost the same clock rate (3.33 GHz) and same price tag as the Core i5-2500. Keep in mind that the Core i5-661 is a dual-core CPU with Hyper-Threading technology, while the Core i5-2500K is a quad-core CPU without Hyper-Threading technology. While both are recognized by the operating system as having “four” cores, on the Core i5-2500K these cores are real, while on the Core i5-661 two are real and two are “simulated.”

We also added the Phenom II X4 970 to our mix, because until yesterday it was the CPU from AMD with the highest clock rate (3.5 GHz), and although it is a little bit cheaper (USD 185.99) than the other CPUs we included, we think users are also curious to see how is the new Phenom II X4 975 compared to the  “old” Phenom II X4 970.

In the tables below you can see a brief comparison between the CPUs we included in our review. AMD CPUs do not support SSE4 instructions (they have a proprietary instruction set called SSE4a, which is not the same thing as SSE4).

CPU Cores HT IGP Internal Clock Turbo Clock Base Clock Core Technology TDP Socket Price
Core i5-2500K 4 No Yes 3.30 GHz 3.7 GHz 100 MHz Sandy Bridge 32 nm 95 W 1155 USD 216
Core i5-661 2 Yes Yes 3.33 GHz 3.6 GHz 133 MHz Clarkdale 32 nm 87 W 1156 USD 210
Phenom II X4 975 4 No No 3.6 GHz 200 MHz Deneb 45 nm 125 W AM3 USD 196
Phenom II X4 970 4 No No 3.5 GHz 200 MHz Deneb 45 nm 125 W AM3 USD 186

TDP stands for Thermal Design Power which advises the user of the maximum amount of heat the CPU can dissipate. The CPU cooler must be capable of dissipating at least this amount of heat.

CPU L1 Cache L2 Cache L3 Cache Memory Support Memory Channels
Core i5-2500K 32 KB + 32 KB per core 256 KB per core 6 MB total DDR3 up to 1333 MHz Two
Core i5-661 32 KB + 32 KB per core 256 KB per core 4 MB total DDR3 up to 1333 MHz Two
Phenom II X4 975 64 KB + 64 KB per core 512 KB per core 6 MB total DDR3 up to 1333 MHz Two
Phenom II X4 970 64 KB + 64 KB per core 512 KB per core 6 MB total DDR3 up to 1333 MHz Two

While all CPUs listed above have an integrated memory controller, only the two Intel CPUs listed have an integrated graphics processor (IGP) and an integrated PCI Express 2.0 controller, handling 16 PCI Express lanes, allowing those CPUs to drive one PCI Express slot at x16 or two PCI Express slots at x8.

Since the Intel CPUs included in our review have an integrated graphics controller, we had to test this aspect of the CPU. We installed the Core i5-661 on an Intel DH55TC motherboard (Intel H55 chipset, USD 90) and the Core i5-2500K on an Intel DH67BL motherboard (Intel H67 chipset, USD 107). Because of that, we installed the AMD CPUs on a motherboard with integrated video on the same price range that we had handy (ASRock 880GXH/USB3, AMD 880G chipset, USD 115).

AMD CPUs talk to the external world (i.e. the chipset) thru a bus called HyperTransport. For a detailed explanation how this bus works, please read our The HyperTransport Bus Used by AMD Processors tutorial.

Socket LGA1156 and 1155 CPUs use the DMI (Digital Media Interface) bus to talk to the chipset, which is the interface previously used to make the connection between the north bridge and the south bridge chips on Intel chipsets.

One final note. The Core i5-2500K has a base clock of 100 MHz instead of using a 133 MHz base clock as the previous Core i5 generation. This means that it has to multiply 100 MHz by 33 to get to its internal 3.30 GHz. The Core i5-661, on the other hand, has to multiply 133 MHz by 25 to get to its internal 3.33 GHz.

Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.