An inside look at the VIA C7-M

Introduction

At last summer’s Computex, VIA introduced the VIA C7 processor and its mobile counterpart, the VIA C7-M processor. These chips sport a thoroughly modern feature set and promise to be a marked advance beyond the VIA C3 processor. More recently, the VIA C7-M ULV (Ultra Low Voltage) processor range was launched at CeBIT (March 2006). The ULV series are essentially the models of C7-M at 1.5GHz and below. For comparison the C7-M processor at 1.5GHz has a maximum power of 12W, whilst the C7-M ULV 1.5GHz model has a maximum power of 7.5W. In all other respects they are the same processor.

For this article we have tested a TwinHead E12BL notebook outfitted with a 1.5GHz C7-M ULV processor and have thoroughly examined the notebook’s performance and power characteristics. Our results show that 1.5GHz C7-M ULV processors consume remarkably little power and sets new industry standards for battery life -- easily outlasting the Intel? Pentium?-M on all of our battery life tests -- while performance is highly competitive in the areas most important for the mobile space.

The VIA C7 die is dwarfed by the Intel's 90nm Pentium-M die. The C7 is in the new nanoBGA2 package, but the chip is also available in the same FCPGA package as the Pentium-M. The state of Texas is not shown to scale. ?

An inside look at the VIA C7-M

The VIA C7-M Processor Overview

Even to the casual observer, the C7-M processor series clearly marks a big advance beyond the old VIA C3 processor design. C7-M processors boast a bleeding-edge instruction set, potent new security hardware, and a brand new, high speed bus that can scale up to 800MHz.

The C7-M, the mobile variety of the C7, is enhanced with top-of-the line power saving support that compliments the advanced 90nm strained silicon IBM SOI process technology upon which all VIA C7 processor’s are built.

Perhaps most impressive is the C7-M's remarkably tiny die. At just over 30 square millimeters, the C7-M is by far the smallest gigahertz capable x86 processor core ever produced. By comparison, the Intel? Pentium?-M and Intel?Celeron?-M Dothan dies are a relatively humongous 88 square millimeters.

The C7-M series inherits the C3’s large 128kB Level 1 cache that is split 50/50 for code versus data. While the C7-M processor’s L2 cache has been doubled beyond the C3 processor, it remains small by today’s standards at 128kB.

Like the C3 and all of AMD’s CPUs, the C7 series have an exclusive, or “victim,” cache structure. This means that the L1 and L2 caches are additive so that, for the C7-M processor, it sees a total of 256kB (128kB L1 + 128kB L2) of cache space. Inclusive cache designs, like Intel’s, are limited to the size of the L2 alone.

The C7-M processor series 128kB L2 is also a 32-way set associative design which reduces miss rates even further and boosts the C7-M processor’s L2 cache's efficiency well beyond the 2x increase in size.