Duel of the Fates: Intel Atom vs Pentium 4

VS

The Contenders;

Intel Pentium 4 (Prescott) 3.2ghz @ 1.6ghz 800Mhz FSB 1MB L2 Cache

Intel Atom N280 (Diamondville) 1.66ghz @ 1.67ghz 533Mhz FSB 512KB L2 Cache

ARCHITECTURAL REVIEW

Pentium 4 utilizes the Netburst architecture which emphasizes on deep instruction pipelining (20 stages on Northwood core and 31 stages on Prescott core) thus achieving a very high clock frequency to curtain the latency of the rather long pipes, while Intel Atom is a Core architecture on a serious diet regime, paying attention on efficient instruction execution and high performance per watt. Below are some comparison of the 2 processors;

• Instruction Issuing

Basically, Pentium 4 can fetch, decode, execute and retire up to 3 instructions per cycle if certain rules are followed while the Atom can issue 2 instruction towards the execution unit at any given time. Prima facie, Pentium 4 has 50% wider instruction width compared to Atom, which will give the Pentium a clear win in any benchmark. However, there are certains speed hacks that Atom utilizes to mask the narrow width, which it inherited from the ultra-fast Core processors

• Battle of the pipes: 31 stage vs 14 stage pipe

Instruction pipeline refers to the series of units that an instruction has to go through in order to be completely executed. Pentium 4 has 31 stage pipe, the longest in microprocessor history. The advantage of long pipes is that more instructions can be fed into the pipes and processor can achieve high frequency. However, long stage pipe are slower; its like riding a bus which has to stop in 31 bus stops vs 14 bus stops. So, Intel Atom pipes is more favourable as it is more efficient pipelining

• Execution Gone Wild: Out of Order vs In Order

Intel Atom execute instruction in an in-order fashion, compared to P4 with more brute design, Out of Order. In simple terms, its like if you had to switch of the lights and start up yr motorcar. If u apply out of order, u will switch off the lights first before starting up the engine as you hv to take the keys before u can start the engine. Out of order principle is to execute 2nd row data that is readily available in the cache while waiting the 1st row data to be fetched, although the 1st row data should be executed first. In performance term, P4's OoO is favourable as it removes execution latency.

• Fusion Tricks: Macro Fusion & Micro Fusion

Atom inherits a novel design from Core architecture, which combines certain instruction into one and executed as one instruction. Micro fusion is introduced in the Pentium M architecture which fuses certain operations(micro ops) into one ops and calculated in the same cycle. Macro Fusion approach is utilized at a bigger level; combining certain instructions as one instruction and executed in the same cycle. This is an advantage for the dual issue Atom as macro fusion allows Atom to at least execute 3 instructions at a given time, comparable to Pentium 4 instruction width.

Benchmarks

*Both processors are running at ~1.6Ghz as to compare the architectural efficiency of both processors.

Processor Arithmetic

Dhrystone ALU (Giga Instruction per Sec. (GiPS))

Whetstone FPU (Gigaflops GFLOPS)

Processor Multimedia (Megapixels/sec.)

Memory Bandwidth (GB/s)

Super PI 1M (shorter time = better)

CONCLUSION

Based on the benchmark results above, Intel Atom wins majority of the tests, thus having a more efficient architecture. Although Atom is an in-order dual issue processor, it can held on its own with a more sophicticated 3 issue wide out of order processor. Having all the novelty design of Core Microarchitecture, Intel Atom is a fast processor in its class without sacrificing on power consumption