Browse Prior Art Database

Separate Look-A-Side Buffer Change Bit Array

IP.com Disclosure Number: IPCOM000037566D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Grosbach, LE: AUTHOR [+3]

Abstract

The Virtual Address Translator (VAT) of a certain computer system uses a fast look-up table to translate virtual addresses. The look-up table consists of the last translated virtual addresses and is called the Look-A-Side buffer (LB). This array allows the Virtual Address Translator (VAT) to write the Look-A-Side Buffer (LB) Change bit without doing a read-modify-write of the Look-A- Side Buffer array and removes a processor cycle required to set the LB Change bit.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 59% of the total text.

Page 1 of 1

Separate Look-A-Side Buffer Change Bit Array

The Virtual Address Translator (VAT) of a certain computer system uses a fast look-up table to translate virtual addresses. The look-up table consists of the last translated virtual addresses and is called the Look-A-Side buffer (LB). This array allows the Virtual Address Translator (VAT) to write the Look-A-Side Buffer (LB) Change bit without doing a read-modify-write of the Look-A- Side Buffer array and removes a processor cycle required to set the LB Change bit.

Whenever microcode specifies a store or set change bit during a virtual address translation, the VAT hardware sets the LB change bit without writing the rest of the LB array entry. The Look-A-Side buffer contains four pieces of data (see Fig. 1). The Segment Identifier (SID) field is the high order 32 bits of the Virtual address of the address in this entry. The Frame Identifier (FID) field is the translated page number. The FID and the low order 9 bits of the Virtual address are concatenated to created the resolved address. The Change Bit (CB) field contains the two change bits for this page. The first change bit is the Primary Directory (PD) change bit. The Primary Directory Change bit is the change bit loaded when the Look-A-Side buffer was loaded from the Primary Directory. The Look-A-Side Buffer change bit is the current state of the change bit for this page.

Whenever an instruction changes a page in Main Store, the Look-A-Side Buffer change bit is set....