Rajat Jain (rajat.noida.india@xxxxxxxxx) wrote: > Hi list, > > I recently read that the concept of "High Memory" was introduced > because certain architectures are capable of physically addressing > larger amounts of memory than they can virtually address (physical > address space > virtual address space). I also read that nowadays > "high Memory" exists only in x86. > > 1) Why is virtual memory > 896 MB on x86 designated as high memory? > AFAIK x86 has 4 GB of virtual address space (=physical address space?) Perhaps I will say some mistakes, please correct me if it is. Kernel map hardware memory addresses as identical in 3GB->4GB in address space by means of paging. So 4GB - 3GB = 1G, if you have more than 1G, kernel must use high memory = mapping and unmapping pages for memory above 1GB. Sorry if it is ugly mistake ;-) > 2) Has the "high Memory" concept got anything to do with PAE (Page > Address Extention) feature of x86? I don't know. > 3) Do any other architectures than x86 have the concept of high memory? Ditto. Have a nice day, -- - Christophe - -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
