| Intel's recently announced group of 486SL Enhanced
microprocessors extend SL-style power management across
the entire 486 line and will eventually replace today's
486DX, 486SX, 486DX2, and 486 OverDrive chips. They also
make it easier for system designers to follow the U.S.
government's Energy Star guidelines. By the end of the
year, power management will be a common feature in desktop
computers as well as portables. In all, Intel (Santa Clara, CA) has announced 10 different 486SL Enhanced processors (see chart), not counting packaging variations. They range from 3.3- and 5-V versions of the 25-MHz 486SX to a 5-V, 66-MHz, clock-doubled 486DX2. All but one are direct replacements for existing 486 chips; the exception is a 3.3-V, 40-MHz, clock-doubled 486DX2 for laptops. Production began in June, except for the 50-MHz 486DX and 66-MHz 486DX2, which are scheduled to ship in the third quarter. Later this year, Intel says it will introduce a 3.3-V version of the 50-MHz 486DX2 and a 100-MHz processor. The new chips are pin-compatible with existing 486 parts, deliver identical performance, work equally well in systems without power management, and cost exactly the same as existing 486s. Most of the forthcoming "green PCs" will use the new Intel chips, as well as compatible processors from Advanced Micro Devices (Sunnyvale, CA) and Cyrix (Austin, TX). All three companies offer chips with a similar range of power-conservation features: SMM (System Management Mode), which allows the CPU to shut down subsystems during idle periods; suspend modes that put the CPU to sleep by slowing or stopping the clock under hardware or software control; and fully static cores that retain information when the CPU is suspended and reawakened. Cyrix includes these features in its 486SLC/e, 486S, and 486S2 chips; the 486SLC has a static core and suspend modes, but no SMM. The AMD 486DXLV-33 also has a full complement of power-management features. In July, AMD was expected to announce a new series of 486-compatible processors that will have power management. Intel's clock-doubled 486SL Enhanced chips introduce a new power-saving mode called Auto Idle that's not found in competing chips. Clock-doubled DX2 processors normally run their internal clock at twice the speed of their I/O bus; for example, a 486DX2-66 runs at 66 MHz internally and 33 MHz externally. The 486SL Enhanced versions of the DX2 can slow the internal clock to match the bus speed during I/O operations, conserving power while the CPU is waiting for data over the bus. Because all these low-power chips can switch in and out of their suspend modes almost instantly, it's possible for the CPU to sleep between keystrokes as you type and then wake up when the next key is pressed. This "active" power management conserves electricity even during normal use. The power saved by suspending a CPU chip is small compared to the energy conserved by shutting off such devices as screens. Still, it offers another way for desktop PCs to minimize electric bills. Intel's Energy-Saving Processors
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