Message-Id: Comments: Authenticated sender is From: "Salvador Eduardo Tropea (SET)" Organization: INTI To: "MNR. LE SMITH" <9813152 AT fharga DOT sun DOT ac DOT za>, djgpp AT delorie DOT com Date: Fri, 3 Apr 1998 13:33:57 +0000 MIME-Version: 1.0 Content-type: text/plain; charset=US-ASCII Content-transfer-encoding: 7BIT Subject: Re: a question In-reply-to: <16742C97815@fharga.sun.ac.za> Precedence: bulk "MNR. LE SMITH" <9813152 AT fharga DOT sun DOT ac DOT za> wrote: > i have recently read a few articles concerning protected mode etc. > > but i still have not yet figured out what the difference is between > linear- and physical address pointers. > > could someone please (briefly) explain to me what the difference is > between linear and physical memory addresses. 386 processors supports the 2 most common protection schemes: 1) Segmentation. 2) Pagination. When the processor uses pages the memory is subdivided in blocks of the same and fixed size called pages. Normally 4Kb (386 support another size too if I remmember well). Each page is located at a physical address and have an entry in one table. This entry says the right access and where this page is mapped in the linear space. So you can remap the address, the linear address may be the same as the physical or not. A good example is the virtual memory: You have more pages in the table than physical pages in RAM, the OS swaps to disk the less used pages and keeps in memory the more commonly used pages. As you can see here some physical page is mapped to one address that isn't the same linear address all the time. SET ------------------------------------ 0 -------------------------------- Visit my home page: http://set-soft.home.ml.org/ or http://www.geocities.com/SiliconValley/Vista/6552/ Salvador Eduardo Tropea (SET). (Electronics Engineer) Alternative e-mail: set-soft AT usa DOT net set AT computer DOT org ICQ: 2951574 Address: Curapaligue 2124, Caseros, 3 de Febrero Buenos Aires, (1678), ARGENTINA TE: +(541) 759 0013