
This is a ram disk for UNIX System V.2, V.3 and System V.4 systems
It has been specifically written for the 286/386 PC versions of UNIX
in particular it has been tested on the following versions (mainly
because I can't get to other versions):

Microport:		System V/AT 286 All Versions
			System V/386	All Versions
Bell Technology:	UNIX System V Release 3.0
Interactive Systems:	386/ix 3.2
SCO:			System V.3
ESIX SYSTEMS:		UNIX System V Release 4.0 Rev  A

However, the driver is pretty generic and should not take much
modification to work on other TRUE AT&T type UNIXes.

It has been used extensively by a number of users since 1987 with
few if any problems, but I will keep watch in comp.sources.bugs
for any feedback.

If anyone changes or modifies this code please send me the details so
that I can pass it on to everyone else. Also I should like to here
about other systems it has been ported to other than those mentioned above.

If you mail your email address I will endevour to keep you informed
of any updates from time to time. (See the file called REGISTER)


INSTALLING:
	Well I have to say that since there are so many 286/386/486
	versions of UNIX/XENIX etc on the market I cannot give
	installation details for each. So it's RTFM I am afraid. Read
	the section in your documentation on how to install device drivers.
	However, Makefiles and installation information is provided
	for the above named systems. Before you start read the INFO.V?
	file for your version of the OS.


MOD INSTALLING 5-10-91 SV4 PORT BY R L BOLIN 

	For SV4.0 see Makefile - You may need to edit
	/etc/conf/cf.d/mdevice for major number devices for the
	RAMDisk (ramd) as default majors are 2 & 26.  Makefile 
	will also work for SV3.2 ISC, ESIX if defined SV3 & i386.

	NOTE: SV4.0 ramd driver - the raminit file is configured for a file
	system of type s5, if you select someother file system you will
	need to adjust the block calculation routine for mkfs.

	BUG: ramstat -m, does not report maxmem correctly - gives 0.  This
	seems to be a BUG in SV4.0 (sysinfo.h).

INFORMATION:

	The ram disk uses a portion of the available user
	memory and configures it as a disk. To the user
	this is totally transparent. The user may read or 
	write to the ram disk in the normal way, indeed
	all standard programs like 'fsck' and 'fsdb' see 
	the ram disk file system just as if it where a file
	system on the hard disk. 


	Obviously you will need enough memory to configure the
	ram disk, the more memory you have the bigger the ram
	disk can be. The ram disk has been designed to allow
	up to 4 virtual disks to reside in memory at any one time.

	The ram disk has undergone some exstensive tests giving
	some amazing results, here is an example: 

	The following criteria was used for the test:

		A 968K Byte C Program in 14 Files, 4 directories, 5 Makefiles
		A PC-AT clone running System V/AT 80286 Running at 12Mhz
		4Mbtye memory fitted
		40 Mbyte Hard disk Average Access 65ms
		Ram disk mounted as /tmp

	RAMDISK SIZE (Blks)	COMPILE TIME (Min:sec)   EFFICENCY RATE
		0			15:09			00%
		500			13:27			12%
		1000			11:36			25%
		1200			09:56			37%
		1500			09:07			40%
		1800			10:17			33%
		2000			11:50			24%
		2200			14:03			07%
		2500			15:37			-2%

	Conclusion
		Because the ram disk resides in memory and not
		on some physical media such as a hard disk,
		the CPU has direct access to the data without
		suffering any latency time. Using a ram disk in
		this way can be upto 40% more efficient especialy
		during developement, However, as the results above
		show, if too much memory is devoted to the ram 
		disk, the efficiency level starts to drop to 
		almost the same level as having no ram disk installed.
		This is because there is a trade off between the
		operating system needing more memory to work with,
		and the ram disk which assignes portions
		of the memory pool to the user, is hogging it all up.

		(If you take too much memory up in the ram disk, you will
		cause the operating system to use the swap device.)

		It can be seen from these results that the ideal
		size of the ram disk for the V.2 installation
		is 1500 physical blocks assuming 4 Mbyte of memory
		is fitted.
		

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	It is VERY IMPORTANT to remember that the ram disk
	resides in memory, this means if the system should
	crash or you should shut the system down without first
	saving the contents of the ram disk, ALL the contents
	of the ram disk WILL have been lost.
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