(12) United States Patent
`Stewart
`
`US006539456B2
`(10) Patent No.:
`US 6,539,456 B2
`(45) Date of Patent:
`*Mar. 25, 2003
`
`(54) HARDWARE ACCELERATION OF BOOT-UP
`UTILIZING A NON-VOLATILE DISK CACHE
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`(75) Inventor: David C. Stewart, Beaverton, OR (US)
`(73) Assignee: Intel Corporation, Santa Clara, CA
`(US)
`
`(*) Notice:
`
`This patent issued on a continued pros-
`ecution application filed under 37 CFR
`1.53(d), and is subject to the twenty year
`patent term provisions of 35 U.S.C.
`154(a)(2).
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`5,307,497 A * 4/1994 Feigenbaum et al. .......... 713/1
`6,061,788 A * 5/2000 Reynaud et al. ............... 713/2
`6,073,232 A * 6/2000 Kroeker et al. ................ 713/1
`6,172,936 B1 * 1/2001 Kitazaki ..................... 365/233
`6,189,100 B1 * 2/2001 Barr et al. .................. 713/182
`6,226,740 B1 * 5/2001 Iga ................................ 713/2
`* cited by examiner
`-
`-
`-
`Primary Examiner—Reginald G. Bragdon
`(74) Attorney, Agent, or Firm—Schwegman, Lundberg,
`Woessner & Kluth, PA.
`(57)
`ABSTRACT
`A computer system includes a nonvolatile memory posi
`tioned between a disk controller and a disk drive storing a
`boot program, in a computer system. Upon a?] initial boot
`(21) Appl. No.: 09/417,000
`sequence, the boot program is loaded into a cache in the
`nonvolatile memory. Subsequent boot sequences retrieve the
`(22) Filed:
`Oct. 13, 1999
`boot program from the cache. Cache validity is maintained
`(65)
`Prior Publication Data
`by monitoring cache misses, and/or by monitoring writes to
`the disk such that a write to a sector held in the cache results
`US 2002/0156970 A1 Oct. 24, 2002
`in the cache line for that sector being invalidated until such
`-
`7
`time as the cache is updated. A filter driver is provided to
`(51) Int. Cl.' ............................ G06F 12/00; G06F 9/24
`monitor writes to the disk and determine if a cache line is
`(52) U.S. Cl. ........................ 711/113; 711/133; 711/144;
`(58) Field of Search
`nº invalidated.
`711/144; 713/2
`
`lelCl 01 ºz?I CI1 .................................
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`38 Claims, 5 Drawing Sheets
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`OS
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`FILTER
`DRIVER
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`DISK
`CONTROLLER
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`CACHE
`CONTROLLER
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`CACHE MAP
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`RAM
`MEMORY
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`BOOT DISK
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`14.
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`U.S. Patent
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`Mar. 25, 2003
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`Sheet 1 of 5
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`US 6,539,456 B2
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`9 |
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`9Z
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`èJETTO?I NOO
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`EHOVO
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`U.S. Patent
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`Mar. 25, 2003
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`Sheet 2 of 5
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`US 6,539,456 B2
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`MARK CACHE LINES INVALID
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`J2
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`LOAD CACHE FROM SECTORS READ DURING
`BOOT SEQUENCE
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`FIG. 2
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`FIG. 3
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`|S CACHE
`DATA VALID?
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`34
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`USE DATA IN
`CACHE FOR BOOT
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`USE BOOT
`PROGRAM ON DISK
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`U.S. Patent
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`Mar. 25, 2003
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`Sheet 3 of 5
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`US 6,539,456 B2
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`- DATA WRITTEN
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`TO BOOT SECTOR
`2
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`3 7
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`YES
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`MARK CACHE
`LINES INVALID
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`8 3
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`REPLACE INVALID DATA
`WITH CURRENT DATA
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`40
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`DETECT CACHE MISSES
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`4.1
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`AGE CACHE TO
`INVALIDATE LINES OF
`CACHE
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`FIG. 5
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`U.S. Patent
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`Mar. 25, 2003
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`Sheet 4 of 5
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`US 6,539,456 B2
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`U.S. Patent
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`Mar. 25, 2003
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`Sheet 5 of 5
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`US 6,539,456 B2
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`- DISK SECTOR
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`CHANGED
`2
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`REFRESH CACHE
`DURING WRITE
`OPERATION TO
`SECTOR
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`61
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`YES
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`|NVALIDATE
`CACHE LINE
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`CORRECT INVALID
`LINE DURING NEXT
`BOOT SEQUENCE
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`FIG. 7
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`1
`HARDWARE ACCELERATION OF BOOT-UP
`UTILIZING A NON-VOLATILE DISK CACHE
`
`US 6,539,456 B2
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`TECHNICAL FIELD OF THE INVENTION
`The present invention pertains generally to computers,
`and more particularly to method and apparatus for speeding
`the boot-up process in computers.
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`BACKGROUND OF THE INVENTION
`Booting up a computer, and in particular an IBM
`compatible personal computer (PC), often takes longer than
`desired. For example, it is not atypical for a PC using the
`Windows(8) 98 operating system to require one minute or
`more to boot up. This delay can be untenable when the PC
`needs to be activated on an expedited basis. For instance, if
`the user needs a phone number quickly, it can be more
`expeditious to look the number up in a telephone directory
`as opposed to a PC if the PC requires booting. Thus, unless
`PC’s can be booted more quickly than as is currently the
`case, their use in applications that require fast initialization
`is limited. Thus, there is a need for a PC with a shorter boot
`up time than is currently available.
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`SUMMARY OF THE INVENTION
`The present invention provides method and apparatus for
`speeding the boot-up of a computer. According to one
`embodiment of the invention, a boot program stored on a
`boot disk is cached in a nonvolatile memory, and retrieved
`by the system from the cache during the boot sequence
`instead of from the boot disk, thereby increasing the speed
`of access to the boot program. This and various other
`embodiments of the invention are described below.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 illustrates a first embodiment of the apparatus of
`the invention.
`FIGS. 2–5 illustrate various alternate embodiments of the
`method of using the cache according to the present inven
`tion.
`FIG. 6 illustrates an alternate embodiment of the appara
`tus of the invention.
`FIG. 7 illustrates yet another embodiment of the method
`of the invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`In the following detailed description of the invention
`reference is made to the accompanying drawings which
`form a part hereof, and in which is shown, by way of
`illustration, specific embodiments in which the invention
`may be practiced. In the drawings, like numerals describe
`substantially similar components throughout the several
`views. These embodiments are described in sufficient detail
`to enable those skilled in the art to practice the invention.
`Other embodiments may be utilized and structural, logical,
`and electrical changes may be made without departing from
`the scope of the present invention.
`Referring now to FIG. 1, there is shown a first embodi
`ment of the invention. A computer system 10 includes a
`Central Processing Unit (CPU) 12, a boot disk 14 storing a
`boot program 16 used by the computer system 10 to boot,
`and a nonvolatile random access memory 18 used as a disk
`cache. Memory 18 receives all or a portion of the boot
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`program 16 from the boot disk 14 and stores it for access by
`the CPU 12 so that the computer system 10 can boot in
`whole or in part from the disk cache in memory 18. A data
`bus 20 couples the CPU 12 to a controller 22 that controls
`the boot disk 14, and a cache controller 24 is coupled
`between the bus 20 and the boot disk 14, and wherein the
`memory 18 is coupled to the cache controller 22. In one
`example embodiment, the computer system 10 may com
`prise an IBM-compatible computer with a Pentium class
`microprocessor and an IDE controller for controller 22, or an
`Apple Macintosh computer with a Motorola microprocessor.
`The invention, however, is not limited in this respect, and
`other types of computer systems and processors can be used.
`Nonvolatile memory 18 may be a FLASH memory, or any
`suitable form of nonvolatile memory, and, preferably in at
`least some embodiments of the invention, random access
`memory.
`In operation, the computer system 10 operates under the
`control of an operating system 26, which includes as a
`portion thereof boot program 16. Boot program 16 has a
`boot-time disk footprint of a ascertainable size. The memory
`18 is sized to be substantially as large as the boot-time disk
`footprint, so that the boot program 16 can be cached in the
`memory 18. However, the memory 18 could be smaller than
`the footprint, and store only a portion of the entire boot
`program 16. Alternatively, memory 18 could exceed the size
`of program 16. All or a portion of boot program 16 can
`therefore be stored in memory 18, from where it can be more
`quickly retrieved, as opposed to being retrieved from the
`boot disk 14, during boot-up of the system 10. If only a
`portion of the boot program 16 is stored in memory 18, that
`portion may be retrieved therefrom, with the remaining
`portion retrieved from the boot disk 14.
`According to another example embodiment, the boot
`program cache in memory 18 is formed of lines, the boot
`program 16 is stored in linear sectors on the boot disk 14,
`and the lines of the cache are mapped to the linear sectors of
`the boot disk 14 read in a boot sequence upon boot up of
`system 10. Referring to FIGS. 2–5, there is shown an
`example method for using the boot program cache. Initially,
`the cache lines are marked invalid (30). The cache is loaded
`with data from sectors of disk 14 read during an initial boot
`sequence (32). As shown in FIG. 3, during boots of the
`system 10 subsequent to the initial boot sequence, data in the
`cache is used (34) instead of the corresponding sector data
`from the boot disk, if the sector data in the cache is valid
`(33). Otherwise, the boot program or the disk is used (35).
`According to another example variant of this embodiment
`shown in FIG. 4, if data is written to a sector read during the
`initial boot sequence (36), the cache lines corresponding to
`the sector are marked invalid (37). The invalid cache line can
`be subsequently replaced with new data from the boot disk
`and the cache line marked valid (38). According to yet
`another example embodiment of the method of the present
`invention, illustrated in FIG. 5, cache coherency is main
`tained by detecting cache misses (40), and if a miss is
`detected, aging the cache, to invalidate lines from the cache
`(41). According to one approach, the cache is aged in a
`first-in first-out (FIFO) manner.
`According to yet another embodiment of the invention
`diagrammatically illustrated in FIG. 6, a filter driver 50 is
`positioned between the operating system 26 and the disk
`controller 22, and the filter driver 50 has access to all
`input-output (I/O) requests to the boot disk 14, and to a
`cache map 52 in cache controller 24. Filter driver 50 can
`detect writes to the disk 14 which are in the same sector as
`a sector in the cache. In one embodiment, filter driver 50 can
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`monitor all I/O operations without significantly slowing
`performance of the system.
`According to a method of operation using the embodi
`ment of FIG. 6, illustrated in FIG. 7, if a disk sector cached
`in the cache is changed (60), as detected by filter driver 50,
`the corresponding cache line is invalidated (61). The invali
`dated line can be refreshed with the correct contents during
`the next boot sequence (62). In one embodiment, the cache
`is not updated by the filter driver so that performance is not
`degraded. However, according to another embodiment, the
`cache is refreshed during the write operation to the corre
`sponding sector in the disk drive (64) using a cache write
`back queue.
`Thus, as described above, there is provided method and
`apparatus for speeding the boot-up of a computer. The
`invention is applicable to all manner of computer systems,
`including appliance-like, sealed case systems, where the
`loadable files and configuration are seldom changed.
`What is claimed is:
`1. A computer system comprising a CPU, a boot disk
`storing a boot program used by the computer system to boot,
`and a nonvolatile memory disk cache receiving all or a
`portion of the boot program from the boot disk and storing
`it for access by the CPU so that the computer system can
`boot in whole or in part from the disk cache, wherein the
`computer system further includes an IDE controller for
`controlling the boot disk, wherein the cache has lines,
`wherein the lines of the cache are mapped to linear sectors
`read in a boot sequence, wherein the cache lines are initially
`marked invalid, wherein the cache is loaded with data from
`sectors read during an initial boot sequence, wherein during
`boots of the system subsequent to the initial boot sequence
`Sector data in the cache is used instead of the corresponding
`sector data from the boot disk if the sector data in the cache
`is valid, and wherein if data is written to a sector read during
`the initial boot sequence, the cache line corresponding to the
`sector is marked invalid.
`2. The computer system of claim 1, wherein the invalid
`cache line is replaced with new data from the boot disk and
`the cache line marked valid.
`3. A computer system comprising a CPU, a boot disk
`storing a boot program used by the computer system to boot,
`and a nonvolatile memory disk cache receiving all or a
`portion of the boot program from the boot disk and storing
`it for access by the CPU so that the computer system can
`boot in whole or in part from the disk cache, wherein the
`computer system further includes an IDE controller for
`controlling the boot disk, wherein the cache has lines,
`wherein the lines of the cache are mapped to linear sectors
`read in a boot sequence, wherein the cache lines are initially
`marked invalid, wherein the cache is loaded with data from
`sectors read during an initial boot sequence, wherein during
`boots of the system subsequent to the initial boot sequence
`sector data in the cache is used instead of the corresponding
`sector data from the boot disk if the sector data in the cache
`is valid, and wherein cache coherency is maintained by
`detecting cache misses, and if a miss is detected, the cache
`is aged, to invalidate lines from the cache.
`4. The computer system of claim 3, wherein the cache is
`aged in a first-in first-out (FIFO) manner.
`5. A computer system comprising a CPU, a boot disk
`storing a boot program used by the computer system to boot,
`and a nonvolatile memory disk cache receiving all or a
`portion of the boot program from the boot disk and storing
`it for access by the CPU so that the computer system can
`boot in whole or in part from the disk cache, wherein the
`computer system further includes an IDE controller for
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`controlling the boot disk, wherein the cache has lines,
`wherein the lines of the cache are mapped to linear sectors
`read in a boot sequence, wherein the cache lines are initially
`marked invalid, wherein the cache is loaded with data from
`sectors read during an initial boot sequence, wherein during
`boots of the system subsequent to the initial boot sequence
`sector data in the cache is used instead of the corresponding
`sector data from the boot disk if the sector data in the cache
`is valid, and wherein the computer system further includes
`a filter driver between the CPU and the IDE controller,
`wherein the filter driver has access to all input-output (I/O)
`requests to the boot disk, and wherein the filter driver has
`access to a cache map and can detect writes to the disk which
`are in the same sector as a sector in the cache.
`6. The computer system of claim 5, further wherein if
`such a sector is changed, the corresponding cache line is
`invalidated, and refreshed with the correct contents during
`the next boot sequence.
`7. The computer system of claim 5, wherein the cache is
`not updated by the filter driver.
`8. The computer system of claim 5, wherein the cache is
`refreshed during the write operation to the corresponding
`sector in the disk drive.
`9. A method comprising storing a boot program used by
`a computer system in a nonvolatile memory disk cache
`which receives all or a portion of the boot program from a
`system boot disk, the boot program stored in the cache for
`access by the CPU so that the computer system can boot in
`whole or in part from the disk cache, wherein an IDE
`controller is used to control the boot disk, wherein the cache
`is organized in lines, and wherein the lines of the cache are
`mapped to linear sectors read in a boot sequence, wherein
`the cache lines are initially marked invalid, wherein the
`cache is loaded with data from sectors read during an initial
`boot sequence, wherein during boots of the system subse
`quent to the initial boot sequence sector data in the cache is
`used instead of the corresponding sector data from the boot
`disk if the sector data in the cache is valid, and wherein if
`data is written to a sector read during the initial boot
`sequence, the cache line corresponding to the sector is
`marked invalid.
`10. The method of claim 9, wherein the invalid cache line
`is replaced with new data from the boot disk and the cache
`line marked valid.
`11. A method comprising storing a boot program used by
`a computer system in a nonvolatile memory disk cache
`which receives all or a portion of the boot program from a
`system boot disk, the boot program stored in the cache for
`access by the CPU so that the computer system can boot in
`whole or in part from the disk cache, wherein an IDE
`controller is used to control the boot disk, wherein the cache
`is organized in lines, and wherein the lines of the cache are
`mapped to linear sectors read in a boot sequence, wherein
`the cache lines are initially marked invalid, wherein the
`cache is loaded with data from sectors read during an initial
`boot sequence, wherein during boots of the system subse
`quent to the initial boot sequence sector data in the cache is
`used instead of the corresponding sector data from the boot
`disk if the sector data in the cache is valid, and wherein
`cache coherency is maintained by detecting cache misses,
`and if a miss is detected, the cache is aged, to invalidate lines
`from the cache.
`12. The method of claim 11, wherein the cache is aged in
`a first-in first-out (FIFO) manner.
`13. A method comprising storing a boot program used by
`a computer system in a nonvolatile memory disk cache
`which receives all or a portion of the boot program from a
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`system boot disk, the boot program stored in the cache for
`access by the CPU so that the computer system can boot in
`whole or in part from the disk cache, wherein an IDE
`controller is used to control the boot disk, wherein the cache
`is organized in lines, and wherein the lines of the cache are
`mapped to linear sectors read in a boot sequence, wherein
`the cache lines are initially marked invalid, wherein the
`cache is loaded with data from sectors read during an initial
`boot sequence, wherein during boots of the system subse
`quent to the initial boot sequence sector data in the cache is
`used instead of the corresponding sector data from the boot
`disk if the sector data in the cache is valid, and further
`wherein a filter driver is positioned between the CPU and the
`IDE controller, and wherein the filter driver has access to all
`input-output (I/O) requests to the boot disk, and wherein the
`filter driver has access to a cache map and can detect writes
`to the disk which are in the same sector as a sector in the
`cache.
`14. The method of claim 13, and further wherein if such
`a sector is changed, the corresponding cache line is
`invalidated, and refreshed with the correct contents during
`the next boot sequence.
`15. The method of claim 13, wherein the cache is not
`updated by the filter driver.
`16. The method of claim 13, wherein the cache is
`refreshed during the write operation to the corresponding
`sector in the disk drive.
`17. A computer system, comprising:
`a CPU;
`a boot disk storing a boot program used by the computer
`system to boot;
`a nonvolatile memory disk cache receiving all or a portion
`of the boot program from the boot disk and storing it for
`access by the CPU, so that the computer system can
`boot in whole or in part from the disk cache; and
`a controller for controlling the boot disk,
`wherein the cache has lines that are initially marked
`invalid, and are mapped to linear sectors read in a boot
`Sequence,
`wherein the cache is loaded with data from sectors read
`during an initial boot sequence,
`wherein during boots of the system subsequent to the
`initial boot, sequence sector data in the cache is used
`instead of the corresponding sector data from the boot
`disk if the sector data in the cache is valid, and
`wherein if data is written to a sector read during the initial
`boot sequence, the cache line corresponding to the
`sector is marked invalid.
`18. The computer system of claim 17, further comprising:
`a data bus coupled to the CPU; and
`a cache controller coupled between the bus and the boot
`disk,
`wherein the disk cache is coupled to the cache controller.
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`19. The computer system of claim 17, wherein the com
`puter system operates under the control of an operating
`system, and wherein the operating system has a boot-time
`disk footprint size and the cache is sized substantially as
`large as the size of the footprint.
`20. The computer system of claim 17, wherein the invalid
`cache line is replaced with new data from the boot disk and
`the cache line marked valid.
`21. A computer system, comprising:
`a CPU;
`a boot disk storing a boot program used by the computer
`system to boot;
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`a nonvolatile memory disk cache receiving all or a portion
`of the boot program from the boot disk and storing it for
`access by the CPU, so that the computer system can
`boot in whole or in part from the disk cache; and
`a controller for controlling the boot disk,
`wherein the cache has lines that are initially marked
`invalid, and are mapped to linear sectors read in a boot
`Sequence,
`wherein the cache is loaded with data from sectors read
`during an initial boot sequence,
`wherein during boots of the system subsequent to the
`initial boot, sequence sector data in the cache is used
`instead of the corresponding sector data from the boot
`disk if the sector data in the cache is valid, and
`wherein cache coherency is maintained by detecting
`cache misses, and if a miss is detected, the cache is
`aged, to invalidate lines from the cache.
`22. The computer system of claim 21, wherein the cache
`is aged in a first-in first-out (FIFO) manner.
`23. The computer system of claim 21, further comprising:
`a data bus coupled to the CPU; and
`a cache controller coupled between the bus and the boot
`disk,
`wherein the disk cache is coupled to the cache controller.
`24. The computer system of claim 21, wherein the com
`puter system operates under the control of an operating
`system, and wherein the operating system has a boot-time
`disk footprint size and the cache is sized substantially as
`large as the size of the footprint.
`25. A computer system, comprising:
`a CPU;
`a boot disk storing a boot program used by the computer
`system to boot;
`a nonvolatile memory disk cache receiving all or a portion
`of the boot program from the boot disk and storing it for
`access by the CPU, so that the computer system can
`boot in whole or in part from the disk cache;
`a controller for controlling the boot disk; and
`a filter driver between the CPU and the controller,
`wherein the cache has lines that are initially marked
`invalid, and are mapped to linear sectors read in a boot
`Sequence,
`wherein the cache is loaded with data from sectors read
`during an initial boot sequence,
`wherein during boots of the system subsequent to the
`initial boot, sequence sector data in the cache is used
`instead of the corresponding sector data from the boot
`disk if the sector data in the cache is valid,
`wherein the filter driver has access to all input-output
`(I/O) requests to the boot disk, and
`wherein the filter driver has access to a cache map and can
`detect writes to the disk which are in the same sector as
`a sector in the cache.
`26. The computer system of claim 25, further wherein if
`such a sector is changed, the corresponding cache line is
`invalidated, and refreshed with the correct contents during
`the next boot sequence.
`27. The computer system of claim 25, wherein the cache
`is not updated by the filter driver.
`28. The computer system of claim 25, wherein the cache
`is refreshed during the write operation to the corresponding
`sector in the disk drive.
`29. A method comprising:
`storing a boot program used by a computer system in a
`nonvolatile memory disk cache that receives all or a
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`portion of the boot program from a system boot disk,
`the boot program stored in the cache for access by a
`CPU so that the computer system can boot in whole or
`in part from the disk cache;
`controlling the boot disk with a controller;
`organizing the cache in lines;
`initially marking the lines of the cache as invalid;
`mapping the lines of the cache to linear sectors read in a
`boot sequence;
`loading the cache with data from sectors read during an
`initial boot sequence;
`using sequence sector data in the cache instead of the
`corresponding sector data from the boot disk during
`boots of the system subsequent to the initial boot if the
`sector data in the cache is valid; and
`marking the cache line corresponding to a sector as
`invalid if data is written to the sector read during the
`initial boot sequence.
`30. The method of claim 29, further comprising providing
`a data bus that couples the CPU to a cache controller coupled
`between the bus and the boot disk, wherein the disk cache
`is coupled to the cache controller.
`31. The method of claim 29, further comprising:
`replacing the invalid cache line with new data from the
`book disk; and
`marking the cache line as valid.
`32. A method comprising:
`storing a boot program used by a computer system in a
`nonvolatile memory disk cache that receives all or a
`portion of the boot program from a system boot disk,
`the boot program stored in the cache for access by a
`CPU so that the computer system can boot in whole or
`in part from the disk cache;
`controlling the boot disk with a controller;
`organizing the cache in lines;
`initially marking the lines of the cache as invalid;
`mapping the lines of the cache to linear sectors read in a
`boot sequence;
`loading the cache with data from sectors read during an
`initial boot sequence;
`using sequence sector data in the cache instead of the
`corresponding sector data from the boot disk during
`boots of the system subsequent to the initial boot if the
`sector data in the cache is valid;
`maintaining cache coherency by detecting cache misses;
`and
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`US 6,539,456 B2
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`8
`if a miss is detected, aging the cache to invalidate lines
`from the cache.
`33. The method of claim 32, further comprising providing
`a data bus that couples the CPU to a cache controller coupled
`between the bus and the boot disk, wherein the disk cache
`is coupled to the cache controller.
`34. The method of claim 32, wherein the aging of the
`cache includes aging the cache in a first-in first-out (FIFO)
`
`Imall?le?.
`35. A method comprising:
`storing a boot program used by a computer system in a
`nonvolatile memory disk cache that receives all or a
`portion of the boot program from a system boot disk,
`the boot program stored in the cache for access by a
`CPU so that the computer system can boot in whole or
`in part from the disk cache;
`controlling the boot disk with a controller;
`organizing the cache in lines;
`initially marking the lines of the cache as invalid;
`mapping the lines of the cache to linear sectors read in a
`boot sequence;
`loading the cache with data from sectors read during an
`initial boot sequence;
`using sequence sector data in the cache instead of the
`corresponding sector data from the boot disk during
`boots of the system subsequent to the initial boot if the
`sector data in the cache is valid; and
`positioning a filter driver between the CPU and the
`controller,
`wherein the filter driver has access to all input-output
`(I/O) requests to the boot disk, and
`wherein the filter driver has access to a cache map and can
`detect writes to the disk which are in the same sector as
`a sector in the cache.
`36. The method of claim 35, and further wherein the cache
`is not updated by the filter driver.
`37. The method of claim 35, further comprising:
`invalidating a cache line if a sector mapped to the cache
`line is changed; and
`refreshing the cache line with correct contents during a
`next boot sequence.
`38. The method of claim 35, further comprising refreshing
`the cache during a write operation to a corresponding sector
`in the disk.
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`Realtime 2018
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