Browse Prior Art Database

Scan Read

IP.com Disclosure Number: IPCOM000089332D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 81K

Publishing Venue

IBM

Related People

Schmitt, SA: AUTHOR

Abstract

The function of a scan read operation in a computer system is to transfer data from storage to a disk storage drive attachment at the same time data is being read from the disk storage drive. The data transferred from storage contains a key, or search argument, which is compared with a key, or search argument, in the data from the disk storage drive. If there is comparison between the keys, or search arguments, a scan hit is indicated, and the operation switches from a scan operation to a read operation, whereby the data from the disk storage drive associated with the key, or argument, causing the scan hit is read into the storage field in main storage associated with the storage key or argument.

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Scan Read

The function of a scan read operation in a computer system is to transfer data from storage to a disk storage drive attachment at the same time data is being read from the disk storage drive. The data transferred from storage contains a key, or search argument, which is compared with a key, or search argument, in the data from the disk storage drive. If there is comparison between the keys, or search arguments, a scan hit is indicated, and the operation switches from a scan operation to a read operation, whereby the data from the disk storage drive associated with the key, or argument, causing the scan hit is read into the storage field in main storage associated with the storage key or argument.

Heretofore, in order to provide switch time for switching from the scan operation to the read operation, special characters, such as hexadecimal FF, immediately followed the key field in main storage, and the scan operation terminated upon detecting the hexadecimal FF characters. That arrangement imposed two constraints, whereby the user of the system had to be aware that if the first character in the storage field was hexadecimal F, scanning would stop immediately. Additionally, the arrangement did not permit the key, or search argument, to be flanked by hexadecimal FF characters. Hence, the key always had to be first in the storage field. In some instances, it may be desirable to have several key fields in storage separated by hexadecimal FF. The present arrangement would then allow a scan operation with respect to the second key.

A typical disk storage drive attachment is shown in Fig. 1. Data from a central processing unit (CPU) is sent to the disk storage drive attachment over data bus out (DBO) 10 and entered into a one-byte buffer 11. The data in buffer 11 can be returned to the CPU via data bus in (DBI) 12, and also be entered into a serializer/deserializer (SERDES) 13. Data from the disk storage drive is in serial form, and it is transferred from the disk storage drive to SERDES 13 and to scan circuits 30 via line 14. Scan circuits 30 can also receive serial data from SERDES 13. As a matter of interest, the serial data from the disk storage drive entered into SERDES 13 can be transferred to the CPU via data buffer 11 and DBI 12.

It should be appreciated that, when in the scan mode of operation, part of the attachment for the disk storage drive is in a read mode, and another part of the attachment is in a write mode. That portion of the attachment associated with receiving data from the CPU would be in the write mode, and that portion of the attachment for receiving data from the disk storage drive would be in a read mode. Cycle steal control 15 is connected to the CPU by interface lines 16 and 17 for controlling direction of data transfers between the CPU and the disk storage drive. It will be recalled that when the scan operation terminates, the entire attachment switches into a read mode, whereby the data entered into...