Saltwell (microarchitecture)

Saltwell (microarchitecture)
Name	Saltwell
Designer	Intel
Produced	From 2012
Predecessor	Bonnell
Successor	Silvermont
Application	Mobile devices, Embedded systems
Process	32 nm
Cores	1–2
L1cache	32 KB (24 KB I, 8 KB D) per core
L2cache	512 KB – 1 MB
Brand name	Intel Atom

Saltwell (microarchitecture). Saltwell is a 32-bit x86 CPU microarchitecture designed by Intel for its low-power Intel Atom product line, serving as a direct successor to the earlier Bonnell core. It was fabricated on a 32 nm process technology and primarily targeted the mobile and Embedded system markets, including Smartphones and tablets. The design focused on improving power efficiency and thermal characteristics over its predecessor while maintaining software compatibility with the vast x86 ecosystem.

Overview

The Saltwell microarchitecture was officially introduced by Intel in late 2012 as part of the Intel Atom Z2460 platform, notably powering devices like the Lenovo K800 smartphone in China and the Lava XOLO X900 in India. It represented Intel's strategic effort to compete in the ARM architecture-dominated Mobile computing space, leveraging the corporation's advanced manufacturing capabilities. The core was a key component of the "Medfield" SoC platform, which integrated the CPU, GPU, and Memory controller onto a single die. This integration was crucial for meeting the stringent space and power constraints of modern Consumer electronics.

Design

Architecturally, Saltwell was an in-order execution design, prioritizing simplicity and power efficiency over the high IPC of out-of-order designs used in Intel Core processors. It featured a dual-issue pipeline, capable of decoding and executing two instructions per clock cycle, and implemented Hyper-threading technology to improve throughput on its typically single or dual-core configurations. The Memory hierarchy included a dedicated 512 KB to 1 MB L2 cache shared between cores, alongside private L1 cache for instructions and data. Key enhancements over Bonnell included improved branch prediction accuracy and more efficient Power management states, allowing for faster transitions into low-power sleep modes.

Process technology

Saltwell cores were manufactured using Intel's 32 nm CMOS process with high-κ metal gate (HKMG) transistors, a significant shrink from the 45 nm process used for Bonnell. This transition, leveraging technology pioneered for the Westmere family, provided substantial reductions in static leakage current and dynamic switching power. The finer geometry allowed for higher transistor density and lower operating voltages, which directly contributed to the microarchitecture's improved Performance per watt metrics, a critical factor for battery-powered devices competing against ARM-based designs from companies like Qualcomm and Samsung Electronics.

Products

Saltwell was marketed under the Intel Atom brand, primarily within the Z2460, Z2480, and Z2760 SoC platforms. These chips were featured in a range of products, including the aforementioned Lenovo K800, the Motorola RAZR i, and tablets like the Acer Iconia Tab W510 and Dell Latitude 10. It also found application in Embedded systems and Industrial PCs, such as those from Advantech and Kontron, where its x86 compatibility and low thermal design power were advantageous. The architecture was later used in select Intel Celeron and Intel Pentium branded processors for the embedded market.

Performance

In performance benchmarks, Saltwell-based processors demonstrated competitive Single-core performance against contemporary ARM Cortex-A9 and early ARM Cortex-A15 designs in certain integer workloads, benefiting from the mature x86 software stack. However, they generally lagged in floating-point performance and graphics capabilities compared to integrated solutions from Imagination Technologies or ARM Mali. Its Hyper-threading implementation provided noticeable gains in multitasking scenarios on platforms like Google Android. The architecture's greatest strength was its power efficiency, enabling all-day battery life in early Intel-based Smartphones, though it ultimately could not match the SoC integration and performance-per-watt of succeeding ARM architecture designs from Apple and Qualcomm.

Successor

Saltwell was succeeded in 2013 by the Silvermont microarchitecture, which represented a major architectural leap for the Intel Atom line. Silvermont introduced an out-of-order execution engine, was built on a new 22 nm Tri-Gate process, and offered significantly higher performance and energy efficiency. This shift was part of Intel's broader response to the competitive pressure from ARM Holdings and the rise of Apple's A-series and Qualcomm Snapdragon processors. The Silvermont core later evolved into Airmont and formed the basis for subsequent Intel Atom, Intel Celeron, and Intel Pentium processors for mobile and low-power segments.

Category:Intel microarchitectures Category:2012 in computing