Disk drive with improved error correction code

In Reed-Solomon error correction code apparatus for a computing system storage device in which useful data written on the surface of a rotating disk in finite blocks is read by a transducing mechanism and in which each finite block of data so recorded includes finite field error correction coding syndrome information appended at the end thereof for enabling detection and correction of errors within the block, an error correction code syndrome generator of minimized logic elements for calculating error correction coding syndrome information in accordance with a Galois field GF(2.sup.8) generated by a field generator polynomial having the form x.sup.8 +x.sup.4 +x.sup.3 +x.sup.2 +1 and wherein the first term of the field is x.sup.5 +x.sup.3 +x+1 (which is 00101011 binary), the generator for testing the calculated information with the appended information to signal any discrepancies indicative of an error within the data block, the generator comprising:

• an input/output summing junction for receiving each incoming data block as a clocked data stream of serial bytes,
• an error correction code feedback path leading from the summing junction and carrying feedback values,
• multiplier apparatus for multiplying the feedback values by a first predetermined constant to yield first product values, for multiplying the feedback values by a second predetermined constant to yield second product values, and for multiplying the feedback values by a third predetermined constant to yield third product values,
• a first clocked latch stage for latching the feedback values present on the feedback path,
• a first summing junction for summing the latched feedback values from the first latch stage with the first product values to yield first sum values,
• a second clocked latch stage for latching the first sum values,
• a second summing junction for summing the first sum values and the second product values to yield second sum values,
• a third clocked latch stage for latching the second sum values,
• a third summing junction for summing the second sum values and the third product values to yield third sum values,
• a fourth clocked latch stage for latching the third sum values,
• the input-output summing junction for summing the third sum values with the incoming clocked stream of serial bytes to generate the feedback values,
• the first, second, third and fourth latch stages being clocked in synchronism with the incoming data stream of serial bytes, and
• testing means for testing the values held in the first, second, third and fourth latch stages at the end of processing of each block thereby to determine if an error has occurred.

A rotating disk data storage subsystem for storing useful data including a rotating disk having a storage surface in which the data is recorded in blocks of predetermined finite length, a positionable data transducer for reading the data of selected data blocks from the surface, a transducer actuator structure for moving the data transducer among data block locations available on the surface in response to data retrieval commands from a host system and for maintaining the data transducer accurately positioned at each data block location in response to servo information obtained from the data surface, a data controller for managing retrieval of data from the surface via the transducer, a buffer memory for temporarily storing each block of data retrieved from the surface, an interface communicating with the host for sending each data block and status commands to the host and for receiving operational commands from the host, a single microprocessor controller for controlling the actuator structure in order to position the transducer,

• each block of data including an error correction code syndrome portion calculated in accordance with a predetermined Galois field error correction algorithm,
• the data controller including a cyclic error correction code syndrome generator for processing each incoming byte of the block in accordance with the said error correction algorithm in a manner which tests for the presence of any errors and which generates error values from which the errors may be located and corrected,
• the microprocessor having access to the data controller for testing to determine if the generator has determined the presence of an error for an incoming block, and if so, for obtaining the error values,
• the microprocessor being programmed to process the error values to determine the location and nature of at least one error, and having access to the buffer memory whereby a data byte of the block including an error may be removed and a corrected byte substituted in its place.