Computer operating system using compressed ROM image in RAM

• US 20020169950A1
• Filed: 06/27/2002
• Published: 11/14/2002
• Est. Priority Date: 12/23/1998
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Cameron J. Esfahani, Paul M. Resch, Ronald Hochsprung, William M. Galcher
• Inventors: Esfahani, Cameron J., Hochsprung, Ronald, Galcher, William M., Resch, Paul M.
• Granted Patent: US 6,732,265 B2
• Time in Patent Office: Days
• US Class Current: 713/2
• CPC Class Codes: G06F 9/4406 Loading of operating system

Abstract

A low-level portion of the operating system of a computer system is separated from an intermediate-level portion of the operating system. The low-level portion, including hardware-specific code, is stored in a relatively small read-only memory (ROM), while at least part of the intermediate-level portion is stored as a compressed ROM image on a disk or other mass storage device, which may be located remotely from the computer system. Upon power-up or reset of the computer system, the code in the ROM is executed to read the compressed ROM image into random access memory (RAM) of the computer system. The compressed image is then decompressed and executed as part of the boot sequence. Once decompressed, the portion of RAM storing the intermediate-level code is write-protected in the memory map, and the code in boot ROM is deleted from the memory map. Memory space in RAM that is allocated to the intermediate-level code but not used is returned to the operating system for use as part of system RAM.

Claims

1. A method of operating a computer system, the computer system including a first storage device and an operating system, the method comprising, as part of initializing the computer system:

loading a compressed first portion of the operating system from a second storage device into the first storage device;

decompressing the compressed first portion of the operating system; and

executing the decompressed first portion of the operating system from the first storage device.

2. A method as recited in claim 1, further comprising maintaining the compressed first portion of the operating system as a separate file in the second storage device prior to said loading.

3. A method as recited in claim 1, wherein the second storage device is located remotely from the computer system.

4. A method as recited in claim 1, wherein the computer system further includes a third storage device, wherein said reading and said storing are performed as a part of executing a second portion of the operating system stored in the third storage device.

5. A method as recited in claim 4, wherein the first storage devices comprises a random access memory, and the third storage device comprises a read-only memory.

6. A method as recited in claim 4, wherein the second portion of the operating system comprises a low-level portion of the operating system, and wherein the first portion of the operating system comprises an intermediate level of the operating system.

7. A method as recited in claim 4, further comprising mapping the first portion of the operating system stored in the third storage device out of a memory space of the computer system after said decompressing.

8. A method as recited in claim 4, wherein executing the first portion of the operating system comprises querying the second portion of the operating system to determine a hardware configuration of the computer system.

9. A method as recited in claim 4, further comprising write-protecting the memory space of the volatile memory device which corresponds to the first portion of the operating system after said decompressing.

10. A method as recited in claim 4, further comprising reallocating a memory space of the first storage device to make unused memory space of the first storage device allocated to the first portion of the operating system available for use by the computer system after said decompressing.

11. A method of operating a computer system, the computer system including a first storage device, a second storage device, and an operating system, the method comprising:

executing a first portion of the operating system stored in the first storage device to cause a second portion of the operating system stored in a storage device other than the first storage device to be read into the second storage device, the second portion of the operating system including a third portion and a compressed fourth portion; and

executing the third portion to cause the fourth portion to be decompressed.

12. A method as recited in claim 11, wherein the first storage device is a read-only memory (ROM) and the second storage device is a random access memory (RAM).

13. A method as recited in claim 12, wherein the first portion of the operating system is a low-level portion of the operating system, and wherein the second portion is an intermediate portion of the operating system.

14. A method as recited in claim 12, further comprising mapping, an address space of the computer system to exclude the first portion of the operating system stored in the ROM memory.

15. A method as recited in claim 12, further comprising write-protecting the memory space of the RAM which contains the decompressed fourth portion.

16. A method as recited in claim 12, further comprising reallocating a memory space of the RAM to make unused portions allocated to the decompressed fourth portion of the operating system available for use by the computer system.

17. A method as recited in claim 12, wherein said executing the first portion and said executing the second portion are performed as part of a boot process of the computer system.

19. A method as recited in claim 18, further comprising mapping an address space of the computer system to exclude the first portion of the operating system stored in the ROM.

20. A method as recited in claim 19, further comprising write-protecting at least part of the memory space of the RAM that contains the decompressed second portion.

21. A method as recited in claim 18, further comprising reallocating a memory space of the RAM to make available unused portions allocated to the decompressed fourth portion of the operating system.

18. A method of operating a computer system, the computer system including a read-only memory (ROM), a random access memory (RAM), and an operating system, the method comprising, as part of an initialization sequence of the computer system:

executing a first portion of the operating system stored in the ROM to locate a second portion of the operating system stored outside the ROM, at least part of the second portion being compressed;

storing the second portion of the operating system in the second RAM;

decompressing the compressed part of the second portion of the operating system;

executing at least part of the second portion of the operating system to;

retrieve first data indicative of a hardware configuration of the computer system from the ROM;

store second data corresponding to the first data in the RAM memory; and

use the second data to dynamically configure the second portion of the operating system.

22. A method of operating a computer system, the computer system including a random access memory (RAM), a read-only memory ROM), a non-volatile storage device separate from the ROM, and an operating system, the method comprising, as part of a boot sequence of the computer system:

executing a first, low-level portion of the operating system stored in the ROM to;

locate a second, compressed portion of the operating system stored in the non-volatile storage device, wherein the second, compressed portion of the operating system is an intermediate-level portion of the operating system; and

store the second portion of the operating system in the RAM;

decompressing the second portion of the operating system;

executing at least part of the second portion of the operating system from the RAM to

query the first portion of the operating system stored in the ROM to determine a hardware configuration of the computer system;

store data indicative of the hardware configuration of the computer system in the RAM; and

exclude the first portion of the operating system stored in the ROM from an address space of the computer system.

24. A device as recited in claim 23, wherein the means for reading the compressed image of the first portion of the operating system code into the RAM comprises means for reading the compressed image of the first portion of the operating system code into the RAM as part of an initialization of the computer system.

25. A device as recited in claim 23, further comprising a read-only memory (ROM), wherein the means for reading the compressed image of the first portion of the operating system code into the RAM comprises means for executing a second portion of the operating system stored in the ROM to read the compressed image from the non-volatile storage device into the RAM.

26. A device as recited in claim 25, further comprising means for querying the second portion of the operating system to determine a hardware configuration of the computer system.

27. A device as recited in claim 25, further comprising write-protecting at least part of the memory space of the RAM which contains the first portion after said decompressing.

28. A device as recited in claim 25, further comprising reallocating a memory space of the volatile storage device to make unused portions allocated to the first portion of the operating system available for use by the computer system after said decompressing.

29. A device as recited in claim 28, wherein the second portion of the operating system stored in the ROM comprises a low-level portion of the operating system, and wherein the first portion of the operating system comprises an intermediate-level portion of the operating system.

30. A device as recited in claim 29, further comprising means for maintaining the compressed image of the first portion of the operating system as a separate file in the non-volatile storage device prior to said reading.

31. A device as recited in claim 29, further comprising means for mapping the low-level portion stored in the ROM out of a memory space of the computer system after said decompressing.

23. A device for use in a computer system, the computer system including a processor and a random access memory (RAM) and operating according to operating system code, the device comprising:

means for reading a compressed image of a first portion of the operating system code from a non-volatile storage device and storing the compressed image in the RAM;

means for decompressing the compressed image of the first portion of the operating system code in the RAM; and

means for executing the first portion of the operating system code from the RAM.

32. A computer system comprising:

a processor for controlling the computer system based on an operating system;

a first memory coupled to the processor;

a second memory coupled to the processor, the second memory having stored therein a first portion of the operating system, including instructions which configure the processor to, as part of a boot sequence of the computer system;

locate and retrieve a second portion of the operating system from a storage device; and

store the second portion of the operating system in the first memory;

wherein the second portion of the operating system includes a third portion and a compressed fourth portion, and wherein the third portion includes instructions which configure the processor to decompress the fourth portion.

33. A computer system as recited in claim 32, wherein the first memory is a random access memory (RAM), and the second memory is a read-only memory (ROM).

34. A computer system as recited in claim 32, wherein the second portion of the operating system further comprises instructions which configure the processor to:

retrieve first data indicative of a hardware configuration of the computer system from the second memory; and

store second data corresponding to the first data in the first memory.

35. A computer system as recited in claim 32, wherein the operating system further comprises instructions which configure the processor to map an address space of the computer system to exclude the first portion of the operating system stored in the second memory.

36. A computer system as recited in claim 35, wherein the operating system further comprises instructions which configure the processor to write-protect at least part of the memory space of the volatile memory that contains the decompressed second portion.

37. A computer system as recited in claim 32, wherein the operating system further comprises instructions which configure the processor to reallocate a memory space of the second memory to make available unused portions allocated to the decompressed fourth portion of the operating system.

39. A computer system as recited in claim 38, wherein the second portion of the operating system further comprises instructions which configure the processor to write-protect at least part of the memory space of the RAM that contains the second portion of the operating system.

40. A computer system as recited in claim 39, wherein the second portion of the operating system further comprises instructions which configure the processor to map an address space of the computer system to exclude the first portion of the operating system stored in the ROM.

41. A computer system as recited in claim 38, wherein the second portion of the operating system further comprises instructions which configure the processor to reallocate a memory space of the RAM to make available unused portions allocated to the second portion of the operating system.

38. A computer system comprising:

a processor for controlling the computer system based on an operating system;

a random access memory (RAM) coupled to the processor;

a read-only memory (ROM) coupled to the processor, the ROM having stored therein a first portion of the operating system, including instructions which configure the processor to, as part of a boot sequence of the computer system;

locate a second portion of the operating system, at least part of which is compressed; and

store the second portion of the operating system in the RAM;

wherein the second portion of operating system includes instructions which configure the processor to;

decompress the compressed part of the second portion of the operating system in the RAM;

retrieve first data indicative of a hardware configuration of the computer system from the ROM; and

store second data corresponding to the first data in the RAM.