TOUGH ONE...I THINK

[nykrybaby97]

Hi again!

I have another question. If BIOS is stored on ROM, and can hold about 65kb of "programs", then what is the need for reserving the last 384kb of the 1st MB of RAM for? I have searched high and low for a solid explantion of this. Please help.

[Rick]

SPEED !!!

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To ERR is HUMAN
To REALLY screw things UP, YOU NEED a COMPUTER !

[ranchdog]

And more speed. Or is that effeciency?

http://www.PCGuide.com/ubb/wink.gif

Luck.

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......Indecision may or may not be my problem......
...... Kickin' A Rock....

[Paleo Pete]

That's upper memory, or the high memory area. (can't remember the exact term and don't have the book handy)

ROM is Read Only Memory, which is a CMOS chip. completely different animal. The upper mamory area is physical RAM (Random Access Memory) and is used to store DOS programs and drivers for faster access by the system, to free more conventional memory. It's also volatile mamory, which means any data stored there is gone when the computer is turned off. ROM keeps its data by use of a battery that supplies power while the computer is turned off.

BIOS is often "shadowed" or copied to RAM for faster access after power up. It can be copied to the upper memory area or to conventional memory, which is the first 640K. Check the PC Guide (http://www.pcguide.com) and look in the topic index, you'll find a good description of conventional memory and how it's used there. Should be some info on the upper memory area too.

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[Dinosaur]

I thought I was prehistoric due to dating to the mainframe and pre-computer era. Now I realize that I am a Dinosaur just for remembering about the early PC era.

BTW: The early PC era repeated a lot of the mistakes of the early mainframe era. It is a crime that those early PC designers knew so little about mainframes. It seems that the hardware people make all sorts of design decisions without knowing enough about software to do their job right.

The 384KB is missing due to compatibility with the early PC architecture. Theo early (original?) PC architecture used the upper 384KB in the first MB of memory to address I/O Ports and the Video Memory. The original architecture could not address beyond the first MB, and they assumed that 640KB would be enough for any program.

I am not certain about the following, but I do not think that memory beyond 640KB really existed. If your code moved something to certain addresses up there, the data actually went into the video memory and was displayed. I think the actual Video memory was on the graphics adapter card. I run a multiple OS system, and occasionally fool around with DOS 6.22 & Windows 3.11. The old DOS programs still manage to control the monitor, even though I have an AGP Video Adapter and DOS always used ISA devices. I assume that the BIOS, CPU, and AGP adapter are still compatible with the old game of pretending that some of the memory beyond 640KB is the display adapter memory. BTW: One of my better DOS graphics programs cannot display more than 16 colors because it asks me to pick my adapter from a list of ISA slot adapters, and my AGP adapter has no driver which will emulate those ISA adapters. There were not enough addresses reserved to cope with 640X480 by 256 colors. I think the original monitors displayed 320X200 in four colors, and some extra addresses were available in anticipation of better technology. Most business computers had monochrome monitors. Who needed color for spreadsheets and word processors?

If you accessed certain addresses, you were actually reading data from a peripheral device.

If you moved data to certain addresses, you were writing information or control data to a peripheral device.Who really knows if it is necessary to maintain this sort of compatibility? Perhaps it must be lived with until the last vestige of DOS goes away.

In those days, you had to use some strange EMS & XMS (Expanded and Extended memory) drivers to use memory beyond one MB, and many applications were not programmed to use those drivers.

DOS 5.00 & later versions would load part of the OS into memory beyond the first MB to allow programs to use more of the first 640KB.

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Gouverneur
Eschew Obfuscation!
If one hundred million people believe a foolish idea, it is still a foolish idea.

[YODA74]

Dinosaur I did not think any of you still existed VERY Impressed THANK YOU. http://www.PCGuide.com/ubb/cool.gif http://www.PCGuide.com/ubb/biggrin.gif http://www.PCGuide.com/ubb/wink.gif

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W/Me (memory eater)
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[RKBA]

Dinosaur,

The first computer I ever had any experience with was an IBM 1401. That was in my third year of college, and I remember in my earlier youth seeing programs about the "astounding" Eniac(?) computer. So I may not date back to the pre-computer era, but I come pretty close. http://www.PCGuide.com/ubb/wink.gif My first computer job shortly thereafter was as a service tech for the RCA Spectra 70 series of computers (an IBM 360 clone).

-- Ron

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Centerfire (http://home.pacbell.net/rsdotson/) ‘‘The natural progress of things is for liberty to yield and government to gain ground.’’ -- Thomas Jefferson