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Mapping Disk Cartridges onto Disk Packs

IP.com Disclosure Number: IPCOM000075259D
Original Publication Date: 1971-Aug-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Grove, MC: AUTHOR [+2]

Abstract

Selector channel commands use program controlled interrupts when mapping IBM 2315 Disk Cartridges onto IBM 1316 Disk Packs. This avoids a delay of one rotation between sectors when transferring successive sectors between the IBM 1800 System memory and the disk device. Programs using the 1810 Disk Drive specify the operation, sector address and number of data words to be transferred. If the 1810 drive is mapped to a 1316 Disk Pack, the mapping function transforms the request into a channel program.

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Mapping Disk Cartridges onto Disk Packs

Selector channel commands use program controlled interrupts when mapping IBM 2315 Disk Cartridges onto IBM 1316 Disk Packs. This avoids a delay of one rotation between sectors when transferring successive sectors between the IBM 1800 System memory and the disk device. Programs using the 1810 Disk Drive specify the operation, sector address and number of data words to be transferred.

If the 1810 drive is mapped to a 1316 Disk Pack, the mapping function transforms the request into a channel program.

The four records in each track of the 1316 Disk Pack that constitutes a mapped 1810 Disk Drive are formatted as shown in Fig. 1. The key stores the sector address. Records are found by searching for an equal comparison on either the count field or the key field. Consider a file protected sector, in which case the key field contains the negative value of the sector address. When data is to be written, the record search is done on the key field and the positive value of the sector address is used for the comparison. When the sector is protected, the search will fail thus providing the necessary file protection. When data is to be read, the search is done on the ID portion of the count field (cylinder, track and record number). The search will be successful and the data can be read.

To read or write successive sectors without the rotational delay, the channel program for sector n+1 is updated while sector n is being transferred. The channel program continues to "loop", reading or writing successive sectors and the channel program is modified for the next sector while a sector is being read or written.

The channel program used for a "write data" of multiple sectors is shown in Fig. 2, where NOP is a "no operation" command used for program compatibility, command chaining and TIC is transfer in channel. When the search is satisfied, the writing of data is begun and immediately a program controlled interrupt (PCI) is generated.

The PCI handling routine:
1) increments the key for next sector address searching.
2) determines if the next sector is on a new track or

cylinder.

a. if so, the seek address is modified and the second TIC

command is set to point to the SEEK command.

b. if not, the second TIC is set to point to the search

command.
3) determines, from the total bytes to be written, if the

next sector will be the last.

a. if not the last, the WRITE DATA command flags of CC

and PCI are left set.

b. if the last, the CC and PCI flags are reset. Thus the channel program is updated, while the previous sector is being written and the channel program "loops" until the channel end, device end interrupt is generated when data for all sectors is written. Other 1810 functions are mapped by use...