amd athlon x2 7850 vs

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AMD Athlon X2 7850 vs. Intel Pentium E5300: Choosing the Best $70 CPU

by Anand Lal Shimpi on 4/28/2009 11:00:00 AMPosted in CPUs Buy the Intel E5300 Pentium Dual Core box

$82.95

AMD celebrates its 40 year anniversary next month, and the Athlon brand turns ten shortlythereafter. What better way to celebrate than by releasing a rebadged 65nm Phenom processorwith two cores disabled at $69? Er, or, I guess they could’ve sent a cake.

It’s called the Athlon X2 7850 and it actually has very little in common with the old Athlon 64X2s. As I mentioned, these are rebadged 65nm Phenom processors with two cores disabled. The

table below should give you a good comparison between the die size and transistor count of theoriginal Phenom compared to the new Athlon X2:

Processor Manufacturing Process Die Size Transistor Count

AMD Phenom X4 9950 65nm 285 mm2 450M

AMD Athlon X2 7850 65nm 285 mm2 450M

There’s no surprise that the specs are identical, because the processors are identical. AMDsimply disables two of the Phenom’s four cores in production before shipping the parts.

In its heyday the original Phenom never broke 2.6GHz, but with a fully mature 65nm processand only two functional cores AMD is able to clock these parts higher. The first dual-corePhenom derivative was the Athlon X2 7750 and it ran at 2.7GHz. In AMD’s tradition of introducing far too many CPUs, today AMD expands the list with a 2.8GHz Athlon X2 7850.

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Once again this is the original Phenom processor; none of the advancements found in thePhenom II are included - it also means that the architecture doesn’t make quite as much sense.



It's a Socket-AM2+ Processor

The original Phenom architecture was designed to be used for quad-core processor designs,hence the use of a large shared L3 cache alongside private L2 caches. With only two cores, manyof the benefits of this architecture are lost. Intel discovered that the ideal dual-core architecturefeatured two levels of cache with a large, fast, L2 shared by both cores. AMD and Intel came tothe conclusion that the ideal quad-core architecture had private L2 caches (one per core) with alarge, shared L3 cache. The Athlon X2 7850 takes the cache hierarchy of the ideal quad-coredesign and uses it on a dual-core processor.



To make matters worse, it does so with an incredibly small L3. Intel found that on its Nehalemprocessor each core needed a minimum of 2MB of L3 cache for optimal performance. WithPhenom II AMD settled on 1.5MB L3 per core. The original Phenom gave each core 512KB of

L3, or in the case of a dual-core derivative 1MB of L3 cache. Again, not ideal.

But it only costs $69.

And things should be easier for AMD at the $69 price point - there’s no Nehalem to worry aboutdown here, only cache starved Core 2 processors. Priced at $74 we have Intel’s Pentium E5300.

It’s a Difference of Cache

The Athlon X2 7850 is based on the original 65nm Phenom core, but with only two coresenabled. That means we’ve got a 64KB L1 data cache, 64KB L1 instruction cache and a 512KBL2 cache per core. There’s also this catch-all 2MB L3 cache, but it’s unfortunately very highlatency by comparison.



The Pentium E5300

The Pentium E5300 is a trimmed down version of Intel’s 45nm Wolfdale core. Each core has a32KB L1 data cache and a 32KB L1 instruction cache, smaller than the Athlon X2. The L2 cacheis shared between the cores and is 2MB in size. It takes just as long to access data from Intel’s2MB shared L2 as it does to get data from AMD’s 512KB L2. Intel does not have an L3 cache but it also doesn’t have an on-die memory controller, so final accesses to memory are a lotslower on Intel’s hardware.



It's all LGA-775

AMD has more cache but it’s slower than Intel’s, once you get out to main memory the AthlonX2 can get to data quicker but the E5300 has the benefit of more advanced prefetchers.



The E5300 is a 45nm chip meaning it can be cooled by Intel's low profile boxed heatsink

Intel’s architecture also has a wider 4-issue front end compared to the Athlon X2. The executionadvantage should go to Intel. With a higher IPC, Intel doesn’t need to run at the same clock speeds to outperform AMD. However with an on-die memory controller, the Athlon X2 could pull ahead in applications that don’t fit nicely within the E5300’s L2 cache.

While the Phenom II has been enjoying clear victories over Intel’s equivalently priced processorsin the higher end space, it looks like crowning a winner at $70 will take a little more work.

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amd athlon x2 7850 vs

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