26 Jul
2001
26 Jul
'01
10:41 a.m.
Zane H. Healy wrote:
[Snip]
Where I see emulation as useful is when you need a laptop version of the
system, or you just don't have a chance of getting the hardware (and/or
don't have the space even if you could). There are also commercial
situations where using a emulator makes good business sense. Oh, the other
use, in the case of the PDP-8 emulators with front panel emulation, is so
that you can see what you should be seeing when running diagnostics on a
system you're trying to repair (when you've never used a PDP-8).
Jerome Fine replies:
While I probably don't really understand someone who's goal is using the
original hardware, on the other hand, I find that any software development
under an emulator is much more straight forward, much easier AND MUCH
FASTER.
For example, on a real 11/83, it takes about 6 minutes to assemble one of the
files I am working on. Even with a Pentium 166 MMX, it takes only a couple
of seconds more than 2 minutes - which is more than long enough to wait.
Plus a full scale test to produce more than a dozen versions on the real hardware
takes more than an hour. Under emulation, under 30 minutes.
Then, there is the use of ram for memory. On the real hardware, I need almost
15 MBytes for a full test. Using real hard drives slows things down. Under
the emulator, with just 128 MBytes of total memory, the RAM: disks provide
me with THREE 32 MByte "disk" drives. I am sure that very little, if any,
new development is taking place for PDP-11 software, but when it does
take place, even if a final checkout on real hardware is needed as the final
step, an emulator seems a bit more practical.
Even when I crash the operating system because of a stupid mistake, I rarely
loose even the VM: disk from the operating system since the emulator boot
code does not clear all of memory as the DEC hardware boot code does.
And although I might lose the emulated hard disks that are in RAM:, I can't
remember the last time that happened. PLUS, since the container files
that represent the starting point of the OS are READ ONLY, they are
never overwritten - I can do that on the real PDP-11 hardware, of course,
but it is less convenient.
Note that I am not trying to contradict Zane where he is looking at the
situation from a hardware point of view, but to add to the software side
of the picture and suggest that an emulator has certain advantages. Mind
you, when I am using a VT320 on a COM: port and I forget that the operating
system has been locked out while the debug program has control, even
with a simple DL emulation, no input characters are lost, although nothing
happens on the output end until normal operation proceeds. With a real
PDP-11, those input characters on a DL channel are just lost.
Sincerely yours,
Jerome Fine