[ale] OT fyi interesting historical info on memory management

[Ron Frazier (ALE)]

Hi all,

Steve Gibson and Leo Laporte just released Security Now episode 410.  It goes over some interesting historical information about the development of hard drives and memory management on intel chips.  It's oriented at the layman / semi-pro, as it usually is, but is interesting nevertheless.  He also talks about some new features that will go into the next revision of Spinrite.

http://twit.tv/show/security-now/410

One interesting thing he shares at the end is basic info about a method which allows a developer to access 4 GB of ram with a modern processor running in real mode.  This is the mode that your bios boots the cpu into initially, before Linux/Win/Mac OS takes over, and the mode that MS-DOS and FreeDos, etc. boot into.  Normally, that mode can only access 1 MB of ram.  But, there is a quirk that can allow access to the full 32 bit address bus, thus allowing up to 4GB.  The details are over my head, but, this could be useful if you're working with a severely resource constrained system and want to boot a very tiny OS but need access to lots of ram for data, etc.  As an example, Steve says his upcoming revision of Spinrite will still run in real mode but will have access to 32 MB track buffers to greatly improve the speed of accessing the hard drive.  They used to be 32 KB.  As an example of what can be done in a very minimal system, Steve's current version of Spinrite occupies 170 KILO Bytes, and has it's own built in multi tasking menu, user interface (text mode), and hdd data processing subsystems.  It also includes a small Windows app which tells you how to make a cd and reboot into it, and the FreeDos OS.  Steve hand coded Spinrite in assembly language.  As a comparison, the Android tablet I'm typing this on, with only the OS, email, and the cpu monitor running, is consuming 300 MEGA Bytes.  I've been threatening to get a book on assembly language and learn it, but I don't know how much I'd need it in the modern world.  Nevertheless, putting an OS, multi tasking hdd diagnostic, and Windows app in 170 KB is pretty impressive to me.

Sincerely,

Ron



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Ron Frazier
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