Browse Prior Art Database

Improved Diskette Save/ Restore

IP.com Disclosure Number: IPCOM000049212D
Original Publication Date: 1982-May-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 4 page(s) / 77K

Publishing Venue

IBM

Related People

Pertzborn, JJ: AUTHOR

Abstract

A RESTORE operation in the IBM System/38 using a diskette takes three revolutions per physical cylinder: one revolution to perform the seek from the previous cylinder (single-track seek), and two revolutions to read the data (one revolution per side). A SAVE operation requires five revolutions per physical cylinder: one revolution to perform the seek from the previous cylinder (single-track seek), two revolutions to write the data (one revolution per side), and two revolutions to verify (CRC check) the data (one revolution per side).

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Improved Diskette Save/ Restore

A RESTORE operation in the IBM System/38 using a diskette takes three revolutions per physical cylinder: one revolution to perform the seek from the previous cylinder (single-track seek), and two revolutions to read the data (one revolution per side). A SAVE operation requires five revolutions per physical cylinder: one revolution to perform the seek from the previous cylinder (single- track seek), two revolutions to write the data (one revolution per side), and two revolutions to verify (CRC check) the data (one revolution per side).

Channel addressing sets up an AL (Address List Element) list containing the storage page addresses required during the READ/WRITE command to store/fetch data from storage. The first address in the ALE is for the first page, as specified by the command element (always Sector phi on Head phi for Save/Restore operations); the second address is for the second page to be transferred, etc.

With past command and channel addressing structure, a half revolution is lost waiting for the diskette to rotate to Sector phi at the completion of the seek. The present arrangement eliminates this half revolution of dead time, thus reducing the SAVE and RESTORE time by a half revolution. The RESTORE time goes from 5 revolutions to 4.5 revolutions, a 10 percent improvement. The SAVE time goes from 3 revolutions to 2.5 revolutions, a 16 percent improvement.

The present arrangement allows the READ and WRITE operations to begin at the first sector found at the completion of the SEEK operation, rather than begin at Sector phi as found within the command element and the addressing structure of the ALE list.

Upon completion of the SEEK operation, the attachment determines the next ID which will be under the READ/WRITE head and available to be read or written. This is done either through an actual read of the ID or by timing out from index and predicting the next ID. At this time, the attachment requests the channel to load the ALE address at the offset from Sector phi into the data IORAR (I/O Resolved Address Register). The READ/WRITE would then begin at this sector an continue in ascending order through the ALE list. The next READ/WRITE command would then perform its seek and begin reading/writing a half revolution offset from the end of the previous operation. The operation just described is illustrated in Fig. 1.

Upon completion of the SEEK operation, as indicated by a signal on line 20 (Fig. 2), the diskette attachment determines the first sector to be read or written. The page offset from the sector specified in the command element is generated by block 30. A CCF (Channel Control Field) is formed by block 40 and passed to the CPU (Central Processing Unit) for execution, i.e., placed on the I/O event stack. The format of the 4-byte CCF:

Byte phi = Function to load an address from the ALE

into the

data IORAR.

1

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Byte 1 = Command register for this Operational

Unit

used by

the event...