4 Jun
2004
4 Jun
'04
9:54 a.m.
> mindless jerks called it
"HD"/"High Density". "HD"/"High Density"
> is MFM at 500K bits per second data transfer rate on a 360
> RPM drive. (Which is exactly what 8" DD was)
On Fri, 4 Jun 2004, Tom Jennings wrote:
Fred, you should stop remembering these things,
it's bad for you.
PS: To this day I can't remember which is which, EXTENDED or EXPANDED
memory, thankfully there's no need to any more.
OK, here's today's dosage of useless obsolete trivia:
"EMS"/"Expanded" memory
is simply bank switching. Even with only 20 bits of address,
almost unlimited memory could be used by switching a little p
iece at a time into a gap inthe memory map. Some of the first
commercial products werethe JRAM boards from Talltree Systems.
Henderson approached me at the West Coast Computer Faire,
and asked if I had written any software that used a lot of memory.
I thought that he was looking for programmers for a contract job.
NO! He was looking for software that NEEDED RAM, in order
to peddle RAM cards. But almost nothing used THAT much RAM.
So, he developed a laser printer interface (JLASER for Canon CX)
that did all of the rasterizing, etc. in the host computer,
and THAT took some RAM!
Then Lotus, Intel, and Microsoft (excluding Talltree!) developed
the "LIM EMS" "Lotus Intel Microsoft Expanded Memory Specification"
"XMS"/"Extended" memory
is simply normal memory accessed by having more than 20 bits
of address bus, and therefore not usable in the Intel Segment:Offset
"REAL MODE" memory addressing system. 286 and 386SX supported
24 bits of address (16M), and a real 386 could theoretically be
made with 32 bits (4G)
"LIMSIM":
It was possible in software to make extended memory behave
like expanded memory, so that REAL MODE software could
still make limited use of extended RAM (for RAMDISK, print spooler, etc.)
"HIMEM":
People noticed that with 21 bits of physical addressing
capability, "REAL MODE" Segment:Offset could overflow to access
almost 64K of additional(extended) memory. Then MICROS~1
"invented" it, and declared that to be THE ANSWER (tm?)
to all "RAM-CRAM" problems, and started PUSHING HIMEM.SYS.
EVERYTHING from MICROS~1 would install it. If you got a
MICROS~1 T shirt, it would try to install it.
Windoze 3.0 was the last version that could run or be installed
without the presence of Extended memory, and therefore was the
last version to be runnable on PC or XT.