Browse Prior Art Database

Device Independent Space Allocation

IP.com Disclosure Number: IPCOM000082751D
Original Publication Date: 1975-Feb-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Bresemann, DH: AUTHOR [+5]

Abstract

The allocation mechanism shown works with a series of bit maps that describe the status of blocks on a storage space. The portion of the storage space described by a single-bit map will be at least an entire disc cylinder, and may be as large as a disc spindle.

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Device Independent Space Allocation

The allocation mechanism shown works with a series of bit maps that describe the status of blocks on a storage space. The portion of the storage space described by a single-bit map will be at least an entire disc cylinder, and may be as large as a disc spindle.

Each N-byte block in the storage space will be described by 2 bits in the bit maps. The correspondence of bit pairs in the bit map to blocks on storage space will be such that, given the device dependent address corresponding to the first bit pair in a map and the offset of a bit pair in the same map, the device dependent address of the corresponding block can be calculated. This calculation will be table driven and should involve only simple modulo-arithmetic
(i.e., offset modulo/cylinder and modulo blocks/track).

The bit pairs corresponding to blocks on storage space have the following meaning: VALUE MEANING 00 Block is available for use (free). 01 Block is in use. 10 Reserved (nay be used for read-only). 11 Block is defective.

The allocation routine accepts commands of the form ALLOCATE (N, X) where: N = The number of bytes to be allocated. X = The storage resource pool from which space is allocated.

On receipt of a command the allocation routine examines the linked bit maps associated with the desired space. The corresponding pointer is passed across the bit pairs until a 00 bit pair is found. At this point (Z), which is the offset of this pair, and (Y), which is the...