Browse Prior Art Database

Technique of Using Compressed Bit-Map for Memory Utilization

IP.com Disclosure Number: IPCOM000120439D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 45K

Publishing Venue

IBM

Related People

Cheng, C: AUTHOR [+2]

Abstract

Disclosed is the invented compressed bit map as a better way of keeping track of the bad memory blocks.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 81% of the total text.

Technique of Using Compressed Bit-Map for Memory Utilization

      Disclosed is the invented compressed bit map as a better way of
keeping track of the bad memory blocks.

      During IPL, the Power On Self Test will check the condition of
the memory.  The results of the test typically are stored in a good
memory area.  Typically, the condition of one memory block (e.g., 16K
bytes/block) on the memory card is represented by 1 bit in the bit
map (e.g., 0 means the block is good and 1 means the block is bad).
The application program checks the bit value of the corresponding
memory block and knows the condition of the memory.

      For computers that have small amounts of memory installed, the
above method presents no serious problem.  As the installed memory
size increases, the bit map size increases proportionally.  As a
result, a substantial amount of memory is needed for the bit map.

      Instead of keeping track of each block by 1 bit, the disclosed
method keeps track of the length of the number of bad blocks of a
certain starting address by n bits (e.g., 8 bits can be used to
represent 256 consecutive bad blocks starting at a certain address).
That is to say, this invention keeps track of the starting address of
the bad block or a series of bad blocks.  The application program
only needs to check the above compressed bad block registration table
and find out whether the memory at the specified address is usable or
not.  The starting address and...