Path: utzoo!attcan!uunet!zephyr.ens.tek.com!tekcrl!terryl
From: terryl@tekcrl.LABS.TEK.COM
Newsgroups: comp.sys.dec
Subject: Re: Why RISC doesn't support large nuber of users?
Keywords: Read between the lines, people
Message-ID: <5554@tekcrl.LABS.TEK.COM>
Date: 8 Feb 90 08:18:25 GMT
References: <25c936b0141@vms.huji.ac.il> <35387@mips.mips.COM> <673@mmlai.UUCP>
Reply-To: terryl@tekcrl.LABS.TEK.COM
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 60


+Summary: one keyboard position right of "L0("
+Three keys on my keyboard are busted, the ones to the right of
+shift-L, 0, and shift-9.  So take "L0(" and shift right one key.
+
     People, here he is telling you "It's a joke, son!!!" (in my best Fog-
horn Leghorn voice!!!). What happens when you take "L0(" and shift that right
one key??? TTAAADDDAAA!!!! :-), a smiley face; and just about everyone fell
for it......

+  >> Altough there are a lot types of RISC machines I hear from most
+  >> suppliers that RISC machine cannot hold a large number of users,
+  >> but very few suppliers claim they can.  So, what is the problem
+  >> with the RISC machines? Context switching,
+
+
+The problem with Reduced Instruction Set Computers is that the
+instruction set determines how many users a computer can handle.
+Some instruction sets (for example, the VAX instruction set) can
+handle a lot of users, while others (like, the i80286 instruction
+set) cannot.  Reduced Instruction Set Computers ("RISC") just don't
+have enough instructions to adequately take care of a large
+set of simultaneous users.   L0(
+
+Think about it; some people say that the Crays were the first RISC
+machines, yet Crays are just batch scheduled compute engines; they
+handle effectively ONE user (!).
+
+You really need to have about 5 or 6 instructions per user, so a
+RISC with its 100-120 instructions tops out at maybe 20-30 users.
+{and have you noticed that they count the different options of
+branches as different instructions?: branch-on-less-than and
+branch-on-greater-than are counted as two instructions.  Seems a
+little bit like cheating, doesn't it?}  On the other hand, a VAX
+has 500 instructions --- and, best of all, it has microcode and
+microinstructions, which count for more.  L0(
+
+The VAX executes a superset of the predecessor machine's (PDP-11's)
+instructions.  In fact the X in VAX stands for eXtension.  So
+the VAX has more instructions than the PDP-11 and it can consequently
+handle more users than the PDP-11 did.
+
+Similarly, the IBM 370 instruction set is a superset of the IBM 360.
+And the 370 handles lots more users than the 360 ever did.
+
+Summary: (# of users) = (1/5) * (# of instructions).
+         This is why RISCs will always be inferior to the VAX and
+         the S/370 in multiuser capability.
+
+This fundamental truth has been kept secret for a long time,
+by the same devilish worldwide conspiracy that first put fluoride
+in drinking water.
+
+A homework problem:  Two VAX machines are the microVAX and the
+VAXstation.  Compare these to the Sun 4/490 computer [SPARC "RISC"
+instruction set] and the MIPS M/2000 computer [MIPS "RISC" instruction
+set] in terms of number of simultaneous users.  Draw a conclusion
+about # of users vs. RISC/VAX instruction sets.
+
+Signing off with a right shift of one keyboard position "L0(" .....