Browse Prior Art Database

Partial Record Read and Write Operations for a Diskette Unit

IP.com Disclosure Number: IPCOM000045425D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Baker, ED: AUTHOR [+5]

Abstract

This mechanism allows a user to read or write portions of a diskette (floppy disk) data record (sector) in a more efficient manner.

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Partial Record Read and Write Operations for a Diskette Unit

This mechanism allows a user to read or write portions of a diskette (floppy disk) data record (sector) in a more efficient manner.

A large diskette record format allows more data to be stored on a diskette than a smaller diskette format. For example, a diskette formatted at 1024 bytes per record can hold 40,000 more bytes than a diskette formatted at 512 bytes per record. Unfortunately, to use these large diskette record formats, a user must have a buffer in the processor main storage equal to the length of the diskette record and there is not always enough processor main storage available for these larger buffers. Thus, a user may not be able to take advantage of the extra data capacity offered by large diskette record formats. The Read Partial and Write Partial commands described herein solve this problem by allowing a user to use the large diskette formats while retaining small processor main storage buffers.

These Read Partial and Write Partial commands allow a user to read or write only a portion of a diskette data record. This read or write operation begins at an offset of 0, 256, 512, or 768 bytes from the beginning of the record and continues until the byte count, specified by the user, goes to zero. There are certain 256- byte offsets that are not allowed, and these are determined by the particular format of the diskette. For example, an offset of 768 bytes would not be allowed on a diskette that was formatted to 512 bytes per record. The allowed offsets are shown in Fig. 2. For example, Offset 2 is 512 bytes. It is allowed on 1024-byte sectors and not allowed on 128-, 256-, or 512- byte sectors.

These commands contrast with a normal diskette read or write command that starts to read or write only from the beginning of the diskette data record. The processing of a Read Partial command begins when the processor sends a command to the I/O controller requesting that a read partial operation be performed. The I/O controller then reads from the diskette the entire diskette record pointed to by the command. This...