From: billg User-Agent: Mozilla/5.0 (OS/2; U; Warp 4.5; en-US; rv:1.4) Gecko/20030624 X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.os.msdos.4dos,comp.os.msdos.apps,comp.os.msdos.desqview,comp.os.msdos.djgpp,comp.os.msdos.mail-news Subject: Re: regarding dos 640kb barrier References: In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Lines: 20 Message-ID: X-Complaints-To: abuse AT usenetserver DOT com X-Abuse-Info: Please be sure to forward a copy of ALL headers X-Abuse-Info: Otherwise we will be unable to process your complaint properly. NNTP-Posting-Date: Mon, 11 Aug 2003 15:55:25 EDT Date: Mon, 11 Aug 2003 16:06:32 -0400 To: djgpp AT delorie DOT com DJ-Gateway: from newsgroup comp.os.msdos.djgpp Reply-To: djgpp AT delorie DOT com yogesh wrote: > everybody knows that dos has 640kb barrier..and hence this makes dos > inefficient... It isn't DOS, it's the chip it was designed to run on. The 8088/8086 can address one megabyte of memory. No operating system running of an 8088/8086 can run code above above the 1-meg line. (Chips that can go into protected mode can use memory above 1-meg as expanded or extended memory, but not as space in which to execute code.) IBM's PC architecture put their ROM BIOS, video memory, etc., in a chunk of memory starting at 640k. Hence, the 640 k limit. Those things had to be within the address space of the 8088/8086, and would have taken the same amount of memory regardless. Interestingly, the immediate successor to the 8086, the 80286, could go into protected mode and address much more memory. Although that ability was largely ignored and the chip was used as a faster 8086, one wonders what would have happened had DOS orignally been coded for a 286 box.