Apparatus and method for prefetching subblocks from a low speed memory to a high speed memory of a memory hierarchy depending upon state of replacing bit in the low speed memory
US4774654A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 24, 1984 |
| Grant date | Sep 27, 1988 |
| Priority date | — |
| Expiry date | Dec 24, 2004 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06F2212/6024
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
A prefetching mechanism for a memory hierarchy which includes at least two levels of storage, with L1 being a high-speed low-capacity memory, and L2 being a low-speed high-capacity memory, with the units of L2 and L1 being blocks and sub-blocks respectively, with each block containing several sub-blocks in consecutive addresses. Each sub-block is provided an additional bit, called a r-bit, which indicates that the sub-block has been previously stored in L1 when the bit is 1, and has not been previously stored in L1 when the bit is 0. Initially when a block is loaded into L2 each of the r-bits in the sub-block are set to 0. When a sub-block is transferred from L1 to L2, its r-bit is then set to 1 in the L2 block, to indicate its previous storage in L1. When the CPU references a given sub-block which is not present in L1, and has to be fetched from L2 to L1, the remaining sub-blocks in this block having r-bits set to 1 are prefetched to L1. This prefetching of the other sub-blocks having r-bits set to 1 results in a more efficient utilization of the L1 storage capacity and results in a highter hit ratio.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.