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Improving Disk Access Speed by Skewing Track Index Organization

IP.com Disclosure Number: IPCOM000075893D
Original Publication Date: 1971-Dec-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Ling, H: AUTHOR [+2]

Abstract

Track index is the lowest level of index and always present. It is written on the first track(s) of the cylinder that it indexed. it is an unblocked, fixed-length record consisting of a count area, a key area and a data area, as shown in Fig. 1.

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Improving Disk Access Speed by Skewing Track Index Organization

Track index is the lowest level of index and always present. It is written on the first track(s) of the cylinder that it indexed. it is an unblocked, fixed-length record consisting of a count area, a key area and a data area, as shown in Fig.
1.

Where the data area contains the normal and overflow information, it is always ten bytes long (8 bytes information, 2 bytes checking.) The data area of the track index is shown in Fig. 2.

The average time required to read a record includes the Track Index (TI) searching time - 1 revolution, half track revolution time for searching the record and record reading time. Total time required to search the /TI and the record is equal to one and a half track resolution time and the record reading time. This method reduces the TI and record searching time by reorganizing the Track Index. The new organization is shown in Fig. 3. Fig. 3 shows the prime area and the track index are on the same track; when the track index is matched, the record can be read within the same revolution.

The overflow area can be set up by the same pattern

Under this particular organization, the index point of the first track has no change, switching of the R/W heads is utilized to search the track index. The space requirement for this skewed-track index organization is equal to that of nonskewed organization. The home address of this new organization serves the same purpose as that of nonskew...