Monitor system for determining the available capacity of a READ buffer and a WRITE buffer in a disk drive system

Claim 2

A data buffer monitoring system in a disk drive system, said disk drive system including a WRITE buffer for storing a plurality of sectors of data received from a host for storage on disks in said disk drive system, a READ buffer for storing a plurality of sectors of data from said disks for transfer to said host and control means for generating a plurality of control signals for controlling the transfer of sectors of data between said host and said disk drive system in response to READ and WRITE requests for the transfer of one or more sectors of data issued by said host to said disk drive system, said data buffer monitoring system comprising: a WRITE buffer monitor for receiving a BLOCK COUNT indicating the number of sectors to be transferred and for generating a WRITE OK TO TRANSFER signal when said WRITE buffer has sufficient available space to store the total number of sectors requested by a WRITE request issued by said host, said WRITE buffer monitor comprises: a held counter for maintaining the count of the number of sectors of data stored in said WRITE buffer which have not been released for transfer to said disk; a released counter for maintaining the count of the number of sectors of data stored in said WRITE buffer which have been released for transfer to said disk; a buffer size register for storing the count of the maximum number of sectors of data that can be stored in said WRITE buffer; a transfer means for generating said WRITE OK TO TRANSFER signal when the sum of said held count in said held register plus said released count in said released counter plus said released BLOCK COUNT is equal to or less than the count in said buffer size register; and a state machine for adding said count in said held counter to said count in said released counter and for making the count in said held counter equal to zero when the sectors of data in said WRITE buffer that were not released for transfer to said disks are released for transfer to said disk; a READ buffer monitor for generating a READ OK TO TRANSFER signal when said READ buffer has in storage the number of sectors of data available for transfer to said host that was requested for transfer by a READ request issued by said host; and transfer controller for generating an OK TO TRANSFER signal to said control means in said disk drive system when said WRITE buffer monitor generates said WRITE OK TO TRANSFER signal and said host has issued a WRITE request and when said READ buffer monitor generates said READ OK TO TRANSFER signal and said host has issued a READ request whereby said control means in response to said OK TO TRANSFER signal controls the transfer of the number of sectors of data from either said host to said WRITE buffer if a WRITE request was issued by said host or from said READ buffer to said host if a READ request was issued by said host.

Claim 3

The data buffer monitoring apparatus of claim 1 wherein: said READ buffer monitor generates a BUFFER FULL signal to said control means in said disk drive system when said READ buffer is full of sectors of data such that the storage of another sector of data in said READ buffer by said control means would overwrite a sector of data that is available for transfer to said host, whereby said control means in response to said BUFFER FULL signal inhibits the further transfer of said sector of data from said disks to said READ buffer until said BUFFER FULL signal is deactivated by said READ buffer monitor means.

Claim 4

The data buffer monitoring apparatus of claim 1 wherein said data buffer monitoring apparatus receives from said control means in said disk drive system: a READ mode signal connected to said transfer controller, said READ MODE signal when high indicates a READ request from said host and when low indicates a WRITE request from said host; a WRITE BLOCK signal connected to said WRITE buffer monitor, said WRITE BLOCK signal when high indicates that sector of data stored in said WRITE buffer can be released for transfer to said disks; a CLOCK signal connected to both said READ buffer monitor and said WRITE buffer monitor; a BLOCK COUNT signal connected to both said READ buffer monitor and said WRITE buffer monitor, said BLOCK COUNT signal indicating the number of sectors of data that are being requested for transfer by either a READ or WRITE request issued by said host; a SECTOR TRANSFER FROM HOST signal connected to said WRITE buffer monitor, said SECTOR TRANSFER FROM HOST signal being generated after each sector of data is transferred from said host to said WRITE buffer; a SECTOR TRANSFER TO HOST signal connected to said READ buffer monitor, said SECTOR TRANSFER TO HOST signal being generated after each sector of data is transferred from READ buffer to said host; a SECTOR TRANSFER FROM DISK signal connected to said READ buffer monitor, said SECTOR TRANSFER FROM DISK signal being generated after each sector of data is transferred from said disk to said READ buffer; a SECTOR TRANSFER TO DISK signal connected to said WRITE buffer monitor, said SECTOR TRANSFER TO DISK signal being generated after each sector of data is transferred from said WRITE buffer to said disks; a MULTIPLE BLOCK signal connected to said READ buffer monitor, said MULTIPLE block signal when high indicating that more than one sector of data is requested to be transferred by either a READ or WRITE request issued by said host and when low indicating that only one sector is requested to be transferred by either a READ or WRITE request issued by said host; and a READ BLOCK signal connected to said READ buffer monitor, said READ BLOCK signal when high indicating a ring mode of operation where the location in said READ buffer is immediately released for the storage of a new sector of data after the sector of data at that location is transferred from the READ buffer to said host and when low indicating a retention mode of operation where a sector of data is maintained in said READ buffer after said sector of data has been transferred from said READ buffer to said host.

Claim 5

The data buffer monitoring apparatus of claim 1 wherein: said state machine generates a series of RELEASE signals equal to the count in said held counter when a WRITE BLOCK signal is changed from low to high; said held counter receives said RELEASE signals and is decremented by one count for each said RELEASE signal received; and said released counter receives said RELEASE signals and is incremented by one count for each said RELEASE signal received.

Claim 6

The data buffer monitoring system of claim 1 wherein: said held counter receives SECTOR TRANSFER FROM HOST signals and is incremented by one count for each said SECTOR TRANSFER FROM HOST signal received; and said released counter receives SECTOR TRANSFER TO DISK signals and is decremented by one count for each said SECTOR TRANSFER TO DISK signal received.

Claim 7

A data buffer monitoring system in a disk drive system, said disk drive system including a WRITE buffer for storing a plurality of sectors of data received from a host for storage on disks in said disk drive system, a READ buffer for storing a plurality of sectors of data from said disks for transfer to said host and control means for generating a plurality of control signals for controlling the transfer of sectors of data between said host and said disk drive system in response to READ and WRITE requests for the transfer of one or more sectors of data issued by said host to said disk drive system, said data buffer monitoring system comprising: a WRITE buffer monitor for generating a WRITE OK TO TRANSFER signal when said WRITE buffer has sufficient available space to store the total number of sectors requested by a WRITE request issued by said host; a READ buffer monitor for generating a READ OK TO TRANSFER signal when said READ buffer has in storage the number of sectors of data available for transfer to said host that was requested for transfer by a READ request issued by said host, said READ buffer monitor comprising: a held counter for maintaining the count of the number of sectors of data stored in said READ buffer which have been released for transfer to said host and are being retained in said READ buffer; a sector counter for maintaining the count of the number of sectors of data stored in said READ buffer, said count including the number of sectors of data being held in said READ buffer and the number of sectors of data stored in said READ buffer that are available for transfer to said host; a buffer size register for storing the count of the maximum number of sectors of data that can be stored in said READ buffer; an adder for generating a summation count equal to sum said count in said held register plus the count in a BLOCK COUNT signal; and a transfer means for generating said READ OK TO TRANSFER signal when the number of sectors of data requested for transfer to said host by a READ request issued by said host is equal to or less than the number of sectors of data in said READ buffer that are available for transfer to said host; and a state machine for reducing said count in said sector counter by the count in said held counter and for reducing the count in said held counter equal to zero when said retained sectors of data in said READ buffer are released thereby providing the locations occupied by said retained sectors of data available for the storage of new sectors of data in said READ buffer; and transfer controller for generating an OK TO TRANSFER signal to said control means in said disk drive system when either said WRITE buffer monitor generates said WRITE OK TO TRANSFER signal and said host has issued a WRITE request or said READ buffer monitor generates said READ OK TO TRANSFER signal and said host has issued a READ request, whereby said control means in response to said OK TO TRANSFER signal controls the transfer of the number of sectors of data from either said host to said WRITE buffer if a WRITE request was issued by said host or from said READ buffer to said host if a READ request was issued by said host.

Claim 8

A data buffer monitoring system in a disk drive system, said disk drive system including a WRITE buffer for storing a plurality of sectors of data received from a host for storage on disks in said disk drive system, a READ buffer for storing a plurality of sectors of data from said disks for transfer to said host and control means for generating a plurality of control signals for controlling the transfer of sectors of data between said host and said disk drive system in response to READ and WRITE requests for the transfer of one or more sectors of data issued by said host to said disk drive system, said data buffer monitoring system comprising: a WRITE buffer monitor for generating a WRITE OK TO TRANSFER signal when said WRITE buffer has sufficient available space to store the total number of sectors requested by a WRITE request issued by said host; a READ buffer monitor for generating a READ OK TO TRANSFER signal when said READ buffer has in storage the number of sectors of data available for transfer to said host that was requested for transfer by a READ request issued by said host, said READ buffer monitor comprising: a held counter for maintaining the count of the number of sectors of data stored in said READ buffer which have been released for transfer to said host and are being retained in said READ buffer; a sector counter for maintaining the count of the number of sectors of data stored in said READ buffer, said count including the number of sectors of data being held in said READ buffer and the number of sectors of data stored in said READ buffer that are available for transfer to said host; a buffer size register for storing the count of the maximum number of sectors of data that can be stored in said READ buffer; an adder for generating a summation count equal to sum said count in said held register plus the count in a BLOCK COUNT signal; and a transfer means for generating said READ OK TO TRANSFER signal when the number of sectors of data requested for transfer to said host by a READ request issued by said host is equal to or less than the number of sectors of data in said READ buffer that are available for transfer to said host; and a state machine for reducing said count in said sector counter by the count in said held counter and for reducing the count in said held counter equal to zero when said retained sectors of data in said READ buffer are released thereby providing the locations occupied by said retained sectors of data available for the storage of new sectors of data in said READ buffer; and transfer controller for generating an OK TO TRANSFER signal to said control means in said disk drive system when either said WRITE buffer monitor generates said WRITE OK TO TRANSFER signal and said host has issued a WRITE request or said READ buffer monitor generates said READ OK TO TRANSFER signal and said host has issued a READ request, whereby said control means in response to said OK TO TRANSFER signal controls the transfer of the number of sectors of data from either said host to said WRITE buffer if a WRITE request was issued by said host or from said READ buffer to said host if a READ request was issued by said host.

Claim 9

The data buffer monitoring apparatus of claim 6 wherein: said state machine generates a series of RELEASE signals equal to the count in said held counter when a READ BLOCK signal is changed from low to high; said held counter receives said RELEASE signals and is decremented by one count for each said RELEASE signal received; and said sector counter receives said RELEASE signals and is decremented by one count for each said RELEASE signal received.

Claim 10

The data buffer monitoring apparatus of claim 6wherein: said held counter receives SECTOR TRANSFER TO HOST signals and is incremented by one count for each said SECTOR TRANSFER TO HOST signal received; and said sector counter receives SECTOR TRANSFER FROM DISK signals and is incremented by one count for each said SECTOR TRANSFER FROM DISK signal received.

Claim 11

The data buffer monitoring apparatus of claim 6 wherein said transfer means comprises: first means for generating a RETENTION SIGNAL OK TO TRANSFER signal when the count in said sector counter is greater than the count in said held counter and a MULTIPLE BLOCKS signal is low; second means for generating a RETENTION MULTIPLE OK TO TRANSFER signal when the count in said sector counter is equal to or greater than said summation count in said adder and said MULTIPLE BLOCKS signal is high; third means for generating a RETENTION OK TO TRANSFER signal whenever either said first means generates said RETENTION SIGNAL OK TO TRANSFER signal or said second means generates said RETENTION MULTIPLE OK TO TRANSFER signal; fourth means for generating a RING OK TO TRANSFER signal when said count in said sector counter is equal to or greater than the count of said BLOCK COUNT signal and said count in said held counter is equal to zero; and fifth means for generating a READ OK TO TRANSFER signal when either said third means generates said RETENTION OK TO TRANSFER signal and a READ BLOCK signal is low or said fourth means generates said RING OK TO TRANSFER signal and said READ BLOCK signal is high.

Claim 12

The data buffer monitoring system of claim 6 wherein said transfer means further comprises: sixth means for generating a BUFFER FULL signal when said count in said sector counter is equal to said count in said buffer size register indicating that the storage of another sector of data in said READ buffer by said control means would overwrite a sector of data that is available for transfer to said host, whereby said control means in response to said BUFFER FULL signal inhibits the further transfer of said sector of data from said disks to said READ buffer until said BUFFER FULL signal is deactivated by said READ buffer monitor means.

Claim 13

The data buffer monitoring apparatus of claim 6 wherein said data buffer monitoring apparatus receives from said control means in said disk drive system: a READ mode signal connected to said transfer controller, said READ MODE signal when high indicates a READ request from said host and when low indicates a WRITE request from said host; a WRITE BLOCK signal connected to said WRITE buffer monitor, said WRITE BLOCK signal when high indicates that sector of data stored in said WRITE buffer can be released for transfer to said disks; a CLOCK signal connected to both said READ buffer monitor and said WRITE buffer monitor; a BLOCK COUNT signal connected to both said READ buffer monitor and said WRITE buffer monitor, said BLOCK COUNT signal indicating the number of sectors of data that are being requested for transfer by either a READ or WRITE request issued by said host; a SECTOR TRANSFER FROM HOST signal connected to said WRITE buffer monitor, said SECTOR TRANSFER FROM HOST signal being generated after each sector of data is transferred from said host to said WRITE buffer; a SECTOR TRANSFER TO HOST signal connected to said READ buffer monitor, said SECTOR TRANSFER TO HOST signal being generated after each sector of data is transferred from READ buffer to said host; a SECTOR TRANSFER FROM DISK signal connected to said READ buffer monitor, said SECTOR TRANSFER FROM DISK signal being generated after each sector of data is transferred from said disk to said READ buffer; a SECTOR TRANSFER TO DISK signal connected to said WRITE buffer monitor, said SECTOR TRANSFER TO DISK signal being generated after each sector of data is transferred from said WRITE buffer to said disks; a MULTIPLE BLOCK signal connected to said READ buffer monitor, said MULTIPLE block signal when high indicating that more than one sector of data is requested to be transferred by either a READ or WRITE request issued by said host and when low indicating that only one sector is requested to be transferred by either a READ or WRITE request issued by said host; and a READ BLOCK signal connected to said READ buffer monitor, said READ BLOCK signal when high indicating a ring mode of operation where the location in said READ buffer is immediately released for the storage of a new sector of data after the sector of data at that location is transferred from the READ buffer to said host and when low indicating a retention mode of operation where a sector of data is maintained in said READ buffer after said sector of data has been transferred from said READ buffer to said host.

Claim 14

A data buffer monitoring system in a disk drive system, said disk drive system including a WRITE buffer for storing a plurality of sectors of data received from a host for storage on disks in said disk drive system, a READ buffer for storing a plurality of sectors of data from said disks for transfer to said host and control means for generating a plurality of control signals for controlling the transfer of sectors of data between said host and said disk drive system in response to READ and WRITE requests for the transfer of one or more sectors of data issued by said host to said disk drive system, said data buffer monitoring system comprising: a WRITE buffer monitor for receiving a BLOCK COUNT from the host indicating the number of sectors to be transferred and for generating a WRITE OK TO TRANSFER signal when said WRITE buffer has sufficient available space to store the total number of sectors requested by a WRITE request issued by said host, said WRITE buffer monitor comprises: a held counter for maintaining the count of the number of sectors of data stored in said WRITE buffer which have not been released for transfer to said disk; a released counter for maintaining the count of the number of sectors of data stored in said WRITE buffer which have been released for transfer to said disk; a buffer size register for storing the count of the maximum number of sectors of data that can be stored in said WRITE buffer; and a transfer means for generating said WRITE OK TO TRANSFER signals when the sum of said held count in said held register plus the released count in said released counter plus said received BLOCK COUNT is equal to or less than the count in said buffer size register; and a state machine for adding said count in said held counter to said count in said released counter and for making the count in said held counter equal to zero when the sectors of data in said WRITE buffer that were not released for transfer to said disks are released for transfer to said disk; a READ buffer monitor for generating a READ OK TO TRANSFER signal when said READ buffer has in storage the number of sectors of data available for transfer to said host that was requested for transfer by a READ request issued by said host, said READ buffer monitor comprises; a held counter for maintaining the count of the number of sectors of data stored in said READ buffer which have been released for transfer to said host and are being retained in said READ buffer; a sector counter for maintaining the count of the number of sectors of data stored in said READ buffer, said count including the number of sectors of data being held in said READ buffer and the number of sectors of data stored in said READ buffer that are available for transfer to said host; a buffer size register for storing the count of the maximum number of sectors of data that can be stored in said READ buffer; an adder for generating a summation count equal to sum said count in said held register plus the count in said BLOCK COUNT signal; and a transfer means for generating said READ OK TO TRANSFER signal when the number of sectors of data requested for transfer to said host by a READ request issued by said host is equal to or less than the number of sectors of data in said READ buffer that are available for transfer to said host; and transfer controller for generating an OK TO TRANSFER signal to said control means in said disk drive system when either said WRITE buffer monitor generates said WRITE OK TO TRANSFER signal and said host has issued a WRITE request or said READ buffer monitor generates said READ OK TO TRANSFER signal and said host has issued a READ request, whereby said control means in response to said OK TO TRANSFER signal controls the transfer of the number of sectors of data from either said host to said WRITE buffer if a WRITE request was issued by said host or from said READ buffer to said host if a READ request was issued by said host.

Claim 15

A data buffer monitoring system in a disk drive system, said disk drive system including a WRITE buffer for storing a plurality of sectors of data received from a host for storage on disks in said disk drive system, a READ buffer for storing a plurality of sectors of data from said disks for transfer to said host and control means for generating a plurality of control signals for controlling the transfer of sectors of data between said host and said disk drive system in response to READ and WRITE requests for the transfer of one or more sectors of data issued by said host to said disk drive system, said data buffer monitoring system comprising: a WRITE buffer monitor for receiving a BLOCK COUNT from the host indicating the number of sectors to be transferred and for generating a WRITE OK TO TRANSFER signal when said WRITE buffer has sufficient available space to store the total number of sectors requested by a WRITE request issued by said host, said WRITE buffer monitor comprises: a held counter for maintaining the count of the number of sectors of data stored in said WRITE buffer which have not been released for transfer to said disk; a released counter for maintaining the count of the number of sectors of data stored in said WRITE buffer which have been released for transfer to said disk; a buffer size register for storing the count of the maximum number of sectors of data that can be stored in said WRITE buffer; and a transfer means for generating said WRITE OK TO TRANSFER signals when the sum of said held count in said held register plus the released count in said released counter plus said received BLOCK COUNT is equal to or less than the count in said buffer size register; and a state machine for adding said count in said held counter to said count in said released counter and for making the count in said held counter equal to zero when the sectors of data in said WRITE buffer that were not released for transfer to said disks are released for transfer to said disk; a READ buffer monitor for generating a READ OK TO TRANSFER signal when said READ buffer has in storage the number of sectors of data available for transfer to said host that was requested for transfer by a READ request issued by said host, said READ buffer monitor comprises; a held counter for maintaining the count of the number of sectors of data stored in said READ buffer which have been released for transfer to said host and are being retained in said READ buffer; a sector counter for maintaining the count of the number of sectors of data stored in said READ buffer, said count including the number of sectors of data being held in said READ buffer and the number of sectors of data stored in said READ buffer that are available for transfer to said host; a buffer size register for storing the count of the maximum number of sectors of data that can be stored in said READ buffer; an adder for generating a summation count equal to sum said count in said held register plus the count in said BLOCK COUNT signal; and a transfer means for generating said READ OK TO TRANSFER signal when the number of sectors of data requested for transfer to said host by a READ request issued by said host is equal to or less than the number of sectors of data in said READ buffer that are available for transfer to said host; and transfer controller for generating an OK TO TRANSFER signal to said control means in said disk drive system when either said WRITE buffer monitor generates said WRITE OK TO TRANSFER signal and said host has issued a WRITE request or said READ buffer monitor generates said READ OK TO TRANSFER signal and said host has issued a READ request, whereby said control means in response to said OK TO TRANSFER signal controls the transfer of the number of sectors of data from either said host to said WRITE buffer if a WRITE request was issued by said host or from said READ buffer to said host if a READ request was issued by said host.

Claim 16

The data buffer monitoring apparatus of claim 12 wherein: said state machine generates a series of RELEASE signals equal to the count in said held counter when a WRITE BLOCK signal is changed from low to high; said held counter receives said RELEASE signals and is decremented by one count for each said RELEASE signal received; and said released counter receives said RELEASE signals and is incremented by one count for each said RELEASE signal received.

Claim 17

The WRITE buffer monitor of the data buffer monitoring system of claim 12 wherein: said held counter received SECTOR TRANSFER FROM HOST signals and is incremented by one count for each said SECTOR TRANSFER FROM HOST signal received; and said released counter receives SECTOR TRANSFER TO DISK signals and is decremented by one count for each said SECTOR TRANSFER TO DISK signal received.

Claim 18

The data buffer monitoring apparatus of claim 12 wherein said READ buffer monitor further comprises: a state machine for reducing said count in said sector counter by the count in said held counter and for reducing the count in said held counter equal to zero when said retained sectors of data in said READ buffer are released thereby providing the locations occupied by said retained sectors of data available for the storage of new sectors of data in said READ buffer.

Claim 19

The READ buffer monitor of the data buffer monitoring apparatus of claim 12 wherein: said held counter receives SECTOR TRANSFER TO HOST signals and is incremented by one count for each said SECTOR TRANSFER TO HOST signal received; and said sector counter receives SECTOR TRANSFER FROM DISK signals and is incremented by one count for each said SECTOR TRANSFER FROM DISK signal received.

Claim 20

The data buffer monitoring apparatus of claim 12 wherein said transfer means of said READ buffer monitor comprises: first means for generating a RETENTION SIGNAL OK TO TRANSFER signal when the count in said sector counter is greater than the count in said held counter and a MULTIPLE BLOCKS signal is low; second means for generating a RETENTION MULTIPLE OK TO TRANSFER signal when the count in said sector counter is equal to or greater than said summation count in said adder and said MULTIPLE BLOCKS signal is high; third means for generating a RETENTION OK TO TRANSFER signal when said first means generates said RETENTION SIGNAL OK TO TRANSFER signal and when said second means generates said RETENTION MULTIPLE OK TO TRANSFER signal; fourth means for generating a RING OK TO TRANSFER signal when said count in said sector counter is equal to or greater than the count of said BLOCK COUNT signal and said count in said held counter is equal to zero; and fifth means for generating a READ OK TO TRANSFER signal when either said third means generates said RETENTION OK TO TRANSFER signal and a READ BLOCK signal is low or said fourth means generates said RING OK TO TRANSFER signal and said READ BLOCK signal is high.

Claim 21

The data buffer monitoring system of claim 12 wherein said transfer means of said READ buffer monitor further comprises: sixth means for generating a BUFFER FULL signal when said count in said sector counter is equal to said count in said buffer size register indicating that the storage of another sector of data in said READ buffer by said control means would overwrite a sector of data that is available for transfer to said host, whereby said control means in response to said BUFFER FULL signal inhibits the further transfer of said sector of data from said disks to said READ buffer until said BUFFER FULL signal is deactivated by said READ buffer monitor means.

Claim 22

The data buffer monitoring apparatus of claim 12 wherein said data buffer monitoring apparatus receives from said control means in said disk drive system: a READ mode signal connected to said transfer controller, said READ MODE signal when high indicates a READ request from said host and when low indicates a WRITE request from said host; a WRITE BLOCK signal connected to said WRITE buffer monitor, said WRITE BLOCK signal when high indicates that sector of data stored in said WRITE buffer can be released for transfer to said disks; a CLOCK signal connected to both said READ buffer monitor and said WRITE buffer monitor; a BLOCK COUNT signal connected to both said READ buffer monitor and said WRITE buffer monitor, said BLOCK COUNT signal indicating the number of sectors of data that are being requested for transfer by either a READ or WRITE request issued by said host; a SECTOR TRANSFER FROM HOST signal connected to said WRITE buffer monitor, said SECTOR TRANSFER FROM HOST signal being generated after each sector of data is transferred from said host to said WRITE buffer; a SECTOR TRANSFER TO HOST signal connected to said READ buffer monitor, said SECTOR TRANSFER TO HOST signal being generated after each sector of data is transferred from READ buffer to said host; a SECTOR TRANSFER FROM DISK signal connected to said READ buffer monitor, said SECTOR TRANSFER FROM DISK signal being generated after each sector of data is transferred from said disk to said READ buffer; a SECTOR TRANSFER TO DISK signal connected to said WRITE buffer monitor, said SECTOR TRANSFER TO DISK signal being generated after each sector of data is transferred from said WRITE buffer to said disks; a MULTIPLE BLOCK signal connected to said READ buffer monitor, said MULTIPLE block signal when high indicating that more than one sector of data is requested to be transferred by either a READ or WRITE request issued by said host and when low indicating that only one sector is requested to be transferred by either a READ or WRITE request issued by said host; and a READ BLOCK signal connected to said READ buffer monitor, said READ BLOCK signal when high indicating a ring mode of operation where the location in said READ buffer is immediately released for the storage of a new sector of data after the sector of data at that location is transferred from the READ buffer to said host and when low indicating a retention mode of operation where a sector of data is maintained in said READ buffer after said sector of data has been transferred from said READ buffer to said host.

Claim 23

The data buffer monitoring apparatus of claim 15 wherein said state machine generates a series of RELEASE signals equal to the count in said held counter when a READ BLOCK signal is changed from low to high; said held counter receives said RELEASE signals and is decremented by one count for each said RELEASE signal received; and said sector counter receives said RELEASE signals and is decremented by one count for each said RELEASE signal received.