What the devil? - Page 1
Forum section: electronics / general

author: Ampera
author_rank: Super Contributor
timestamp: November 26, 2016, 10:55:16 pm
content: So, I built an 80486 AM486 based gaming machine. It's a great machine, running ZDoom sweet, and even giving quake a run for it's money!Just for anybody walking by who saw my previous post, I am working on the video, I have had some setbacks including my AWE64 being a crippled OEM version, that I combined with the incorrect memory as opposed to what I purchased into return money I used to buy an AWE32. Still working on it, video will be done once I have that all said and done.So what's the big deal? Well I am going to put a link to a picture of the board and CPU I bought and am using.http://ipic.su/img/img7/fs/DSC_0230.1472798114.jpgBeautiful board, and beautiful chip. These would have not been cheap in 1995 I can tell you that. But look at the CPU model number for me.AM486-DX4-100-SV8BLet me decode that for youAM486 indicates it's an AMD 486 based CPU.DX4 is the family of 486 chips.100 indicates the stock clock speedS indicated it is an "Enhanced" 486V indicates 3.3 V requiring a compatible motherboard.8 indicates8KiBof cacheand B indicates that cache is Write-Back.So what is the big deal? Well the seller was nice enough to give me some benches, here is one of interest.http://ipic.su/img/img7/fs/DSC_0054.1472798129.jpgThis benchmark indicates it has 16K of cache, what gives? Maybe it's thinking it's a different model, or possibly an intel DX4-100, but that's odd.So I got the board, paired with a dual channel IDE MI/O card and a 2MB Diamond Stealth SE, this thing is flying off the bloody walls. I then got to testing this machine with Phil'sComputerLab's DOS benchmarking kit. It has a built in memory testing system that will test memory, and L1 and L2 CacheResults?32MB of memory, which is in there perfectly fine and working.256K of L2 cache, which it has.And 16K of L1 cache. I don't get it. How could this be true?I checked on the bottom as a suggestion by a family member to see if it might have been a binned chip that could have been unlocked? No. Everything is pristine and looking as fine as it does in the picture. It has a heatsink on it that I prefer not to take off ATM, but it's the same chip as true as my word can be taken here. It has no signs of tampering, no signs of a relabel or anything.To add as a caveat, the Norton system ID program (Forgot what it's really called) claims it's a 105Mhz Cyrix processor, but that's so outrageous it can't be true (It's running at 120MHz, and it's a damn sight faster than a Cyrix chip) Oh well, one bench is basing it off 286/287 speeds, so who knows.But this is damn odd, I refuse to believe it's a fake of some sort, why would someone make a fake chip, go through all sorts of trouble to give it the right badging and everything, and make it better than the chip they are faking?Is it a possible misprint? Did they have a set of dies that went into the wrong packaging, or wrong labeling machine and nobody noticed over 20 years ago? I have no clue, and it's not that I'm complaining, it's that I am interested as to how this could have 16k of L1 Cache.AMD DID make a 16k cache version (SV16B) but I do not have a chip labeled as such, and this is not an Intel chip that had 16K of cache always.Any ideas?

author: MK14
author_rank: Super Contributor
timestamp: November 26, 2016, 11:16:20 pm
content: Apparently, the 8Kb cache is used forBOTH, data and instructions.Later/modern processors, seem to quote the level 1 cache size as the sum of both data and instruction caches.So your measurement software, may be detecting theSAMEcache for both data and instructions, and giving 8 + 8 = 16Kb. Which is correct for later/modern chips, but the AMD method ofsharingthem, for that era chip, has not been handled correctly by your measurement software.One of the Sources:http://www.cpu-world.com/CPUs/80486/AMD-Am486DX4-100V16BGI.htmlhttp://www.cpu-world.com/Glossary/L/Level_1_cache.htmlQuotetl;drIt might be seeing the 8Kb cache twice, once for data, and once for instructions, and hence saying 16Kb.N.B. Or I could be completely wrong.

author: MK14
author_rank: Super Contributor
timestamp: November 26, 2016, 11:34:45 pm
content: Update:Actually, this seems to say that the (later) WB version, which I think you have. Has 16Kb cache, anyway.https://en.wikipedia.org/wiki/Am486QuoteBut maybe the rest of your OP post is in conflict with this. It is a bit big to easily take in one go, sorry.Part of your post, which says "WB", here:http://ipic.su/img/img7/fs/DSC_0054.1472798129.jpg

author: Ampera
author_rank: Super Contributor
timestamp: November 26, 2016, 11:48:49 pm
content: Quote from: MK14 on November 26, 2016, 11:34:45 pmThere was a 16 and 8 KiB L1 cache model. SV8B (On my chip) indicates 8KiB of WB cache. However the previous thing you said could be correct. Who know, I don't know of something that can measure it accurately.

author: amyk
author_rank: Super Contributor
timestamp: November 27, 2016, 12:10:20 am
content: If it is actually an enhanced Am486, you should be able to get more info on it via CPUID instruction:http://datasheets.chipdb.org/AMD/486_5x86/19720C.pdf(page 15)

author: TerraHertz
author_rank: Super Contributor
timestamp: November 27, 2016, 12:16:28 am
content: Quote from: TwoOfFive on November 26, 2016, 10:55:16 pmAh, the VL bus. Haven't seen one of those for a while.Is that a NOS 1990s board, or is someone making them recently?If it's that old, I'd suggest replacing the NiCd battery as they tend to leak when old, and seriously corrode all the nearby circuitry.Now you only need three more systems the same to set up a four machine DOOM network, with a coax bus LAN. Oh god, how many hours did my kids and I enjoy in that game?

author: Ampera
author_rank: Super Contributor
timestamp: November 27, 2016, 12:35:57 am
content: Quote from: TerraHertz on November 27, 2016, 12:16:28 amNiCad battery is brand new, and I am keeping an eye on it before I replace it with something else.