Deep and Deeper Sleep States
Deep sleep (C3) and Deeper sleep (C4) are terms used in the power management of mobile platforms. Power management of mobile platforms is all about improving battery life. The idea is to put the CPU to "sleep" when it is not in use. C3 "deep sleep" and C4 "deeper sleep" are ACPI power mangement states. Deeper sleep comes from improvements in CPU and chipset interaction to redirect snoop cycles so that the CPU stays in deep C4 state longer, resulting in lower power consumption while idle.

CPU/Package sleep states

C0 - Active: CPU is on. C0 is the operating state.

C1 - Auto Halt: core clock is off. C1 is a state where the processor is not executing instructions, but can return to an executing state essentially instantaneously. Some processors also support an Enhanced C1 state (C1E) for lower power consumption.

C2 - Stop Clock: core and bus clocks are off. C2 is a state where the processor maintains all software-visible state, but may take longer to wake up.

C3 - Deep Sleep: clock generator is off. C3 is a state where the processor does not need to keep its cache coherent, but maintains other states. Some processors have variations on the C3 state (Deep Sleep, Deeper Sleep, etc.) that differ in how long it takes to wake the processor.

C4 - Deeper Sleep: reduced VCC

DC4 - Deeper C4 Sleep: further reduced VCC

ACPI (Advanced Configuration and Power Interface)*
Located on the System Manageability Bus, the ACPI enables low-power sleep mode and conserves energy when a system is idle.

Power Management
Refers to how power is efficiently directed to different components of a system. Power management is especially important for portable devices that rely on battery power. By reducing power to components that aren't being used, a good power management system can double or triple the lifetime of a battery.

Deeper Sleep
Works along with Intel® QuickStart Technology on Intel mobile processors. Deeper Sleep is a dynamic power management mode that delivers longer battery life. Deeper Sleep minimizes the power consumption of the CPU when it senses an extended period of inactivity by the user, reducing power when idle and quickly restoring the CPU to an active state as soon as the user resumes use of the PC. It reduces processor voltage below the minimum operating voltage while preserving the processor state. Deeper Sleep is functionally identical to the Deep Sleep State but at a 66% lower voltage.

QuickStart Technology
Extends battery life by entering a low-power state during the briefest pauses in user activity, such as between key strokes, and returning instantly to full-power state when prompted.

Enhanced Intel® Deeper Sleep with Dynamic Cache Sizing
This new power savings mechanism flushes system memory dynamically, based on demand or during periods of inactivity. Power savings occur as the cache ways are turned off once the data has been saved in memory. Because L2 cache data integrity determines Deeper Sleep minimum voltage limits for the Intel Core Duo processor, once the Dynamic Cache Sizing feature flushes the entire L2 cache to memory, the processor transitions to a new power management state. This is called Enhanced Intel® Deeper Sleep, and allows the processor to lower voltage below the Deeper Sleep minimum voltage for enhanced power savings and/or efficiencies.

This applies to:

Intel® Core™ Duo Processor Intel® Core™ Solo processor Intel® Core™2 Duo Mobile Processor Intel® Pentium® M Processor Intel® Pentium® Processor for Mobile Mobile Intel® Celeron® Processors Mobile Intel® Pentium® 4 Processors - M