Path: utzoo!utgpu!watmath!att!occrsh!uokmax!apple!snorkelwacker!tut.cis.ohio-state.edu!gem.mps.ohio-state.edu!brutus.cs.uiuc.edu!rpi!unix.cie.rpi.edu!vicc From: vicc@unix.cie.rpi.edu (VICC Project (Rose)) Newsgroups: comp.sys.ibm.pc Subject: Re: Ami Bios and the V20 Message-ID: <1989Nov17.060155.26381@rpi.edu> Date: 17 Nov 89 06:01:55 GMT References: <6129@merlin.usc.edu> <206900136@prism> <2851@phred.UUCP> Reply-To: vicc@unix.cie.rpi.edu.UUCP (VICC Project (Rose)) Organization: CIE, Rensselaer Polytechnic Institute, Troy, NY Lines: 65 In article <2851@phred.UUCP> brianr@phred.UUCP (Brian Reese) writes: >In article <206900136@prism> rob@prism.TMC.COM writes: >> >> It's been said before, but it's worth repeating - The 1.8 number from >>SI is unrealistic (in general, any number from SI comparing different >> >> In general, a V20 should give you about a 5 - 10% speedup, possibly > ^^^^^^ >>as high as 20 - 30% when running floating point code, which tends to be > >Have you ever actually _tried_ it? I replaced the CPU in my XT with a V20 >and realized very noticable increase in speed, running a variety of apps. >If the increase was only 5 - 10%, I really doubt that I would notice it. >I'd say, on the average, I got a 40 - 50% boost. (Just for GP, it went >from 1.0 to 1.8, just like the original poster.) Actually, from examining NECs timing, it would seem that an increase of 20-30% could be expected. Multiplies and divides run 4x faster. All Effective Addresses take 2 clock cycles, instead of 6+ (the V20 has hardware address calculation as opposed to microcode) The V20 also does multiple shifts at 1 cycle per bit instead of 4 because of hardware aid to the microcode (ie - not a barrel shifter which would do all shifts in 1 cycle. A number of instructions are also 1 or 2 cycles quicker. Of course these numbers are affected by the instruction cache (which I think might be better on the V20 also) REP instructions are also speeded up, prefix interrupts are handled correctly (up to 3 prefixes are 'remembered' as opposed to only 1 on the 8086 - but the V20 adds a REPC [carry] or REPNC so you could have 4 - but - most people dont use the LOCK prefix) As I said before the V20 has all 80186 instructions. In addition the V20 has REPC, REPNC, bit field instructions, BCD arithmetic string functions, and 8080 emulation (either mode shift or SW interrupt) Since someone asked for the number for NEC: 1-800-632-3531 (or 3532 in California) Ask for the V20 User's Manual One complaint I have about the manual: the registers are renamed, and the instructions are renamed (probably a copyright problem) One question I have: there is also a 2nd Co-Processor Escape op-code, does anyone know what this does? (could it support a 387 or something weird - neat like that? (I doubt it but one could hope)) One note I picked up from a friend - if you send your system in for repairs, make sure that they pull the V20 if they replace your system board, my friend lost his V20 because of that (so now he has a handfull to take care of all future problems - also purchased when it looked like the supply would dry up real fast) A note about the speed up - a register to memory operation is typically 15 cycles or so on the V20 and 13+EA on the 8088, which translates to a 20% speedup at worst. This is what I base my 20-30% speedup on, most instructions are not MUL or DIV, but many are MOV reg,mem or OP reg,mem. -- Frank Filz Center For Integrated Electronics Rensselaer Polytechnic Institute vicc@unix.cie.rpi.edu