Non-volatile disk cache

A method of restoring the data contained in an electrically erasable programmable read-only memory (EEPROM) to a computer system device coupled to a computer system comprising:

• a. determining a last location in the EEPROM at which valid device data resided;
• b. writing to the device all data starting at the last location which was modified but not written to the device contained in the EEPROM;
• c. determining whether there is sufficient memory in the EEPROM to store additional data from a volatile cache memory coupled to the EEPROM, and if there is not, erasing the EEPROM;
• and
• d. determining whether the number of erasures of the EEPROM has exceeded a first value, and if it has, inhibiting the computer system from writing to the EEPROM.

An apparatus for use in a computer system comprising:

• a. a volatile cache memory;
• b. a non-volatile memory for receiving data contained in said volatile cache memory during a power interruption;
• c. a detection circuit for detecting said power interruption in said computer system;
• d. a copying circuit coupled to said volatile cache, said non-volatile memory, and said detection circuit, said copying circuit for copying a first set of data contained in said volatile cache memory to said non-volatile memory upon detection of said power interruption, wherein said first set of data includes only data that has not been written-back to a device coupled to said volatile cache memory;
• and
• e. a power circuit coupled to said volatile cache memory, said non-volatile memory and said copying circuit, said power circuit being independent of said computer system power and having sufficient capacity to power said volatile cache memory and said copying circuit for the duration of an operation to copy said first set of data contained in said volatile cache memory to said non-volatile memory upon said detection of said power interruption.

A computer system comprising:

• a. a volatile cache memory;
• b. a non-volatile memory for receiving contents of said volatile cache memory during a power interruption;
• c. a detection circuit for detecting said power interruption in said computer system;
• d. a copying circuit coupled to said volatile cache, said non-volatile memory, and said detection circuit, said copying circuit for copying said contents contained in said volatile cache memory to said non-volatile memory upon detection of said power interruption, wherein said copying circuit copies only contents of said volatile cache memory which have not been written-back to a device coupled to said volatile cache memory;
• and
• e. a power circuit coupled to said volatile cache memory, said non-volatile memory and said copying circuit, said power circuit being independent of said computer system power and having sufficient capacity to power said volatile cache memory and said copying circuit for the duration of an operation to copy said contents of said volatile cache memory to said non-volatile memory upon said detection of said power interruption.

A method in a computer system of storing the data contained in a volatile cache for a device coupled to the computer system to an electrically erasable programmable read-only memory (EEPROM) upon losing computer system power comprising the following steps:

• a. detecting a power loss in the computer system;
• b. determining a first location in the EEPROM, the first location being the last location in the EEPROM at which data was written;
• and
• c. writing a first set of data from the volatile cache into the EEPROM starting at the last location, the first set of data comprising only data which has been modified but has not been written to the device.