Abstract:
A computer system that optimizes the power efficiency of a portable computer system is described. Specifically, the secondary memory of the system is partitioned. A standard hard disk drive is used to store lower utilization applications, while a micro storage unit is used to store high utilization applications.

Description:
FIELD OF THE INVENTION 
   The present invention pertains to the field of computer design. More particularly, the present invention relates to a method for optimizing power in a portable computer system. 
   BACKGROUND OF THE INVENTION 
   A computer system typically comprises a main memory and a secondary memory. Main memory or random access memory (RAM) refers to the physical system that is internal to the computer. The computer manipulates only the data that is in main memory. Therefore, programs that are executed and files that are accessed are typically copied into main memory. When the computer system is powered off, the data in main memory is typically not retained. The amount of main memory in a computer system determines how many programs can be executed at one time and how much data can be readily available to a program. 
   In contrast to main memory, the data in secondary memory is typically retained even after the system is powered off. Secondary memory allows large amounts of data to be stored. Examples of secondary memory include mass storage devices such as hard disks, floppy disks, optical disks, and tapes. 
   The secondary memory of a portable computer system typically comprises a single hard disk drive (HDD). The HDD consumes approximately 9% of a computer system&#39;s power. Approximately 90% of the battery life of a portable computer system is currently consumed during system boot-up and by an idle operating system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an embodiment of a computer system having a tiered secondary architecture; 
       FIG. 2  is a flowchart for optimizing the power consumption of a computer system having a tiered secondary architecture; and 
       FIG. 3  is a graph of the power optimization of a computer system having a tiered secondary architecture in comparison with a computer system having a single secondary memory. 
   

   DETAILED DESCRIPTION 
   In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention. 
   HDDs consume power even when idle. Most traditional HDDs are 20 gigabytes or greater. Applications of a computer system may be stored in the hard disk drive. An application may comprise data and instructions. 
   In comparison to traditional HDDs, mini-HDDs store less data. For example, a mini-HDD may store one gigabyte of data. However, mini-HDDs may consume less power and provide higher reliability. Therefore, a system that utilizes a mini-HDD in addition to a traditional HDD may provide power savings by allowing the traditional HDD to be powered off during idle. The mini-HDD may be used for storing highly utilized applications. 
     FIG. 1  depicts a system having a tiered secondary memory architecture. CPU  110  is coupled to main memory  120 , level 2 cache  130 , and chipset  140 . The CPU  110  may comprise an on-chip level 1 cache. The level 2 cache  130  temporarily stores data and instructions transferred to and from the CPU  110 . Chipset  140  is coupled to SCSI host adapter  150 . The SCSI host adapter  150  is coupled to a traditional HDD  160  and a mini-HDD  170 . Both the traditional HDD  160  and the mini-HDD  170  are internal to the system. 
   Applications that are often accessed are stored in mini-HDD  170 . Moreover, the operating system may also be stored on the mini-HDD  170 . At powerup, the operating system may be loaded from the mini-HDD  170 . Less often used applications are stored in the traditional HDD  160 . Thus, when the CPU  110  wants to run an application from the mini-HDD  170 , the applications are obtained from the traditional HDD  160  or the mini-HDD  170 . The chipset  140  comprises buffers and memory address decoders to enable the CPU  110  to communicate with the traditional HDD  160  and the mini-HDD  170 . The chipset  140  may also comprise a plurality of counters to track the number of times each application on the system is used. This enables the system to determine which applications are to be stored in the mini-HDD  170 . For this embodiment of the invention, the mini-HDD may have a five gigabyte storage capacity. 
   The user may determine which applications are to be stored in mini-HDD  170 . For instance, applications that the user deems to be most important may be stored in mini-HDD  170 . Alternatively, the system may determine which applications are most important by the frequency of use. 
   The bridge between the chipset  140  and the traditional HDD  160  and the mini-HDD  170  may be a small computer system interface (SCSI) bus. If a SCSI bus is used, a SCSI host adapter  150  may be used to send and receive messages on the SCSI bus. The SCSI host adapter  150  may also check at powerup to confirm that the traditional HDD  160  and the mini-HDD  170  are properly connected to the bus. 
   Alternatively, the traditional HDD  160  and the mini-HDD  170  may be integrated device electronics (IDE) drives. The traditional HDD  160  and the mini-HDD  170  may be coupled to the chipset  140  without connection to a SCSI bus. The traditional HDD  160  and the mini-HDD  170  may comprise the control and interface electronics necessary to connect directly to the chipset  140 . 
   For one embodiment of the invention, the system of  FIG. 1  is a battery powered portable computer system. For another embodiment of the invention, the system is a cellular phone. 
     FIG. 2  depicts a flowchart for optimizing the power consumption of a computer system having a tiered secondary architecture. Following system powerup  205 , the applications run by the system are tracked in operation  210 . The tracking may be performed by the operating system or a tracking circuit. The tracking circuit may comprise a plurality of counters or a state machine. The tracking circuit may be built using combinational logic. The tracking circuit may be integrated as part of the chipset  140 . Operation  220  then determines if the system is in a power optimization mode. If the system is in a power optimization mode, then the applications that have a high utilization are moved to the mini-HDD  170  in operation  230 . High utilization may be defined as applications that have been accessed the most number of times during a given time period. Operation  260  powers off the traditional HDD  160  when the traditional HDD  160  is idle to conserve power. Operation  210  continues to monitor application usage and moves applications to the mini-HDD  170  when appropriate. The traditional HDD  160  may be powered back when the system receives a request to access data from the traditional HDD  160 . 
   If the system is not in a power optimization mode, operation  240  checks if the system is in a performance optimization mode. Some applications may offer improved performance if accessed from the traditional HDD  160 . Thus, if the system is in a performance optimization, then the high utilization applications may be placed on the traditional HDD  160 . 
   For another embodiment of the invention, the system automatically moves the high utilization applications to the mini-HDD  170  without determining whether the system is in a power optimization mode or a performance optimization mode. 
     FIG. 3  depicts a graph of the power optimization of a computer system having a tiered secondary architecture in comparison with a computer system having a single secondary memory. X-axis represents a percentage utilization of a mini-HDD. Y-axis  320  represents the power saved in watts over a system having only a traditional HDD. A system having a mini-HDD may reduce power consumption during all states including active, idle, and suspend. In addition, power savings may be achieved during bootup. Each of the curves  330 ,  340 , and  350  represent a system that utilizes both a mini-HDD and a traditional HDD. Curve  330  is a system that has 60 percent of its applications&#39; capacity stored on a mini-HDD and 40 percent of its applications&#39; capacity stored on a traditional HDD. Curve  340  is a system that has 80 percent of its applications&#39; capacity stored on a HDD and 20 percent of its applications&#39; capacity stored on a traditional HDD. Curve  350  is a system that has 90 percent of its applications&#39; capacity stored on a HDD and 10 percent of its applications&#39; capacity stored on a traditional HDD. 
   Curve  350  shows the greatest overall power savings over a system utilizing only a traditional HDD. For instance, when the mini-HDD of a system having 90 percent of its applications&#39; capacity stored on the mini-HDD has 100 percent utilization, the system may conserve approximately 1.4 watts over a system that only uses a traditional HDD. In comparison, curve  340  shows that a system having 80 percent of its applications&#39; capacity stored on a mini-HDD saves approximately 1.3 watts over a traditional HDD system at 100 percent utilization. Curve  330  shows that a system having 60 percent of its applications&#39; capacity stored on a mini-HDD saves approximately 0.95 watts over a traditional HDD system at 100 percent utilization. Each of the curves  330 ,  340 , and  350  show a reduction in power savings as the percentage utilization of the mini-HDD decreases. The less the mini-HDD is utilized, the more likely that the traditional HDD is not idle and thus consuming power. Power conservation may help to extend the battery life of the system. 
   In the foregoing specification the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modification and changes may be made thereto without departure from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.