Message-Id: <199705160257.WAA17246@mail.storm.ca> Comments: Authenticated sender is From: "Yves Bellefeuille" To: opendos AT delorie DOT com Date: Thu, 15 May 1997 22:57:18 -0400 MIME-Version: 1.0 Content-type: text/plain; charset=US-ASCII Content-transfer-encoding: 7BIT Subject: Re: 16 vs. 32-bit performance Reply-to: opendos AT delorie DOT com In-reply-to: <199705151828.OAA00071@delorie.com> Precedence: bulk > That's why 32-bit disk access improves things an amazing amount under > Windows 3.11 and a SCSI drive, and doesn't do much at all for an old > IDE. Let's see if I can explain about "32-bit disk access". DOS uses BIOS routines to access the display, keyboard, hard disk, diskette, COM port and printer. Say a program wants to read a file from the hard disk. It asks the BIOS to get the information. The BIOS sends the request to the disk adapter then waits for the information to come back. "Is it there yet? No. Is it there yet? No." After some delay the information finally arrives and the system goes back to doing useful work. If you're a single user doing word processing, this doesn't matter. If you're on a network with 20 other users, then it's a big problem. It means that the entire system stops every time you read a file. This is why servers can't use DOS and BIOS to access the hard disk. Novell made its money with Netware by offering a multi-tasking, BIOS-avoiding operating system when Microsoft and IBM only had DOS-based servers. The evolution of Windows has been to eliminate BIOS one step at a time. Windows 3.1 already used its own devices rather than DOS services to access the display, the mouse and the keyboard. The next step was for Windows to access the hard disk itself. This was done with Windows for Workgroups 3.11. With 32-bit disk access, Windows manipulates the hard disk directly, without using BIOS. Note the name "Windows for Workgroups": the difference between Windows 3.1 and WfWG 3.11 is that WfWG no longer uses BIOS to access the hard disk, but this single difference means that Windows for the first time becomes suitable for workgroups and networks. (As it happens, WfWG 3.11 only has 32-bit disk access for IDE disks. SCSI disk support had to wait until Windows 95.) So the deal with 32-bit disk access isn't really that you can read data twice as fast if you read it 32 bits at a time rather than 16 bits at a time. Rather, the significance is that you're no longer using BIOS and stopping the entire system every time you read something on a disk. A single user might not see a big difference, but it's crucial on a multi-user system. So once again "32-bit" is generally better than "16-bit", but not as much as the hype implies, and perhaps not enough to matter to the average user. Regards, -- Yves Bellefeuille See homepage for best freeware for DOS and Win 3.1x Ottawa, Canada Finger, homepage or key-server for PGP key an448 AT freenet DOT carleton DOT ca Francais / English / Esperanto http://www.ncf.carleton.ca/~an448/