Aucbvax.6324
fa.works
utcsrgv!utzoo!decvax!ucbvax!works
Sat Feb 27 15:41:59 1982
IBM PC Review
>From COMSAT.SoftArts@MIT-Multics Sat Feb 27 15:34:16 1982
Original to: WORKS at MIT-MC
Via: Mit-Mc; 27 Feb 82 17:27-EDT
Via: Brl-Bmd; 27 Feb 82 17:32-EDT
I have spent quite a bit of time using the IBM PC, and use it
full time as a terminal on my host machine (with the PC running
a vt100 (subset) emulator at 19200 baud). I have a vt100
to the right of my IBM PC; it is typically used only when
I happen to need 132 mode.
I find the keyboard to be one of the best that I have ever typed
on, with the possible exception of one or two PLATO keyboards.
The positive mechanical feedback is a dream. Yes, it took me
several weeks to get used to the single-width shift keys (and
thus the placement of the back-slash key), but now I can type
circles around a vt100.
I bind the keys on the various keypads to various EMACS
functions, and use the right pad extensively (arrows and page
keys). The left pad, in my opinion, suffers greatly because it
was not designed with enough room to put a "template" around it.
The IBM monochrome monitor suffers from a terrible lack of
contrast. We have reduced this problem by putting a $200
Polaroid CP-70 Contrast Enhancement Filter over the display.
I have not yet been exposed to the color monitor.
I am not impressed with the processor speed. The programs that
we have converted from z80 to the 8088 do not run much faster,
primarily because of the 8-bit data path. The instruction set
is obviously better than the 8-bit machines. As Seth noted,
however, dealing with 64k segments is a tremendous pain. This
is, of course, not IBM's fault, though the 8-bit bus IS.
A MAJOR problem with the IBM is the lack of board slots
available. This limits the amount of memory to 512k, or
typically 256k. You must trade off peripherals for memory.
The IBM sorely needs a hard disk.
The IBM hardware beats the hell out of the previous generation
8-bit systems. All peripherals interrupt through a very handy
8259a programmable interrupt controller. There are three hardware
clocks: one to refresh memory, one used for DOS timer services
(and to time out the disk), and the last to provide a tone
generator to play music. The machine provides a socket for the
8087 floating point processor. The color graphics card uses
the (fairly flexible) 6845 CRT controller. The disk controller
is a NEC uPD765. All in all, it is a very high quality piece
of hardware, and very nice to work with.
The ASYNC interface is satisfactory. The supplied driver in ROM
is a polling driver, and is not much good for many applications.
NOTE: If you attempt to write your own interrupt-enabled driver,
you may get very frustrated. If you ever want an interrupt from
the 8250, you must set bit 3 (OUT 2) of the Modem Control Register.
This is documented as a "user-designated output", where the user
is IBM, and the designation is to inhibit interrupts(!). The only
place that you can find this out is by looking at the schematic on
page D-48 of the Technical Reference Manual.
IBM DOS is satisfactory. Disk error recovery is pretty good, but
other error recovery is marginal. For example, "break"ing during
program image activation will frequently cause DOS to crash. The
function calls have all seemed to work "as documented". The
"end but stay resident" function call is very handy for those of
us who wish to write device drivers that stay around. It also
enables one to write a very nice "histogramming" program that
stays resident during user program execution.
Last but not least, I must CHEER for IBM with regards to the $36
"Technical Reference Manual". It has EVERYTHING you ever wanted
to know about the machine: schematics, chip write-ups, chip and
connector pin-outs, configuration info, LISTINGS OF THE ROM,
etc. IBM should be complimented for making all of this info
available in an inexpensive, well-put-together manual.
Ray Ozzie (Ozzie.SoftArts)
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