Browse Prior Art Database

Tape Drive Attachment Support

IP.com Disclosure Number: IPCOM000052756D
Original Publication Date: 1981-Jul-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 4 page(s) / 138K

Publishing Venue

IBM

Related People

Larson, WA: AUTHOR [+3]

Abstract

In the past, a single request for a tape operation had to be expanded into several device commands. A write request, for example, became three device commands, i.e., mode set to insure proper tape density, load I/O to indicate the block size, and write for writing the data. This entire sequence had to be repeated for each block of data written. Additionally the system program had to keep several statistics, such as the number of reads, etc. The present arrangement for the tape drive attachment reduces system program overhead and supports the operations of write, read, read backward, forward space block, backward space block, forward space file, backward space file, erase gap, write tape mark and data security erase.

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Tape Drive Attachment Support

In the past, a single request for a tape operation had to be expanded into several device commands. A write request, for example, became three device commands, i.e., mode set to insure proper tape density, load I/O to indicate the block size, and write for writing the data. This entire sequence had to be repeated for each block of data written. Additionally the system program had to keep several statistics, such as the number of reads, etc. The present arrangement for the tape drive attachment reduces system program overhead and supports the operations of write, read, read backward, forward space block, backward space block, forward space file, backward space file, erase gap, write tape mark and data security erase.

The tape drive or drives 100 (Fig. 1) connect to adapter 50 which in turn is connected to an I/O controller (IOC) 40. IOC 40 connects to the channel 30 of the computer system which includes central processing unit (CPU) 25, control storage 15 and main storage 10. The command consists of 8 bytes having a format as in Fig. 4. The command is structured by the system program and is transferred from main storage 10 via channel 30 into the IOC channel buffer 45 (Fig. 2A). Command execution, including the fetching of the command block 200, is illustrated in Fig. 3. The second step of command execution is to save the command data (block 201) by moving it one byte at a time from the channel buffer 45 to the local storage registers (LSRs) of data storage 46 (Fig. 2B). Control storage 55 contains the microcode for the IOC 40, and this microcode sends a mode set command (block 202) to the tape drive 100 by placing appropriate information into external registers 60 of adapter 50. The mode set had been specified by a prior mode set command to the attachment and specifying the mode has to be done once per session.

A command code stored in LSRs 46 is interrogated (block 203) by execution of microcode from control storage 55. If the command is data security erase, an erase gap command is issued to the tape drive 100, as represented by block 205 in Fig. 3. This ensures that the tape drive is in write status, which is a requirement for execution of the data security erase command.

If the command is a data transfer command, i.e., read, read backward or write, the microcode issues a load I/O command to tape drive 100, as in block 204. For all other commands, i.e., forward space block, forward space file, etc., control goes to block 206 for execution of the operation.

For a load I/O command, the microcode sends a load I/O command to the tape drive 100. This command informs the tape drive of the block size of the next block to be written or read. The block size is specified in bytes 4 and 5 of the command to the attachment and was saved in LSRs 46. When an erase gap command is given, the microcode sends an erase gap command to the tape drive 100 to ensure that it is in the w...