View Full Version : Anybody got a BIOS-chip with a MK number ending in something else than "N-#"?

March 12th, 2010, 02:54 PM
Most IBM BIOS chips I have seen so far are of different kinds, but some them appear more frequently than others.

One of the most frequent ones are the Motorola-produced ones. They doesn't bear a chip ID, so all information present is the IBM part number, copyrigth, problably a 2 digit manufacturing code (XE), and the datecode. The other most frequent one are the ones most problably produced by Mostek. They have a chip ID starting with "MK" and location of manufacture in addition to all the info present on the Motorola variants. The 2 digit code is also ZA instead of XE.

Then there are some produced by AMI, and problably a few other companies too. However, I don't have enugh referances to those to say anything spesiffic there.


In the beginning I thought that only Plastic versions of the chips were used, however, that has been disproved after I got my early XT. One of the BIOS chips there were produced by (problably) Mostek, but it was in the form of a purple gold-topped cheramic DIP. I found this unusual. The only real difference I see from it's plastic counterpart, is that the MK number ends with "P-25" instead of "N-25" or "N-4" as they usually do.

+-------------------------------+ +-------------------------------+
| MK37050N-4 | | |
| 5000027 | | (M) 5000027 |
\ /-\ ZA /-\ | \ /-\ (C)1983 IBM CORP /-\ |
/ \-/ (C)IBM 1982 \-/ | / \-/ XE \-/ |
| D MALAYSIA | | 8430B NM |
| 8303 E | | o |
+-------------------------------+ +-------------------------------+

+--------+============+---------+ +-------------------------------+
| |MK38035 P-25| | | MK38036N-25 |
| | 1501512 | | | 1501512 |
\ |Z A | | \ /-\ ZA /-\ |
/ |(C)IBM 1982 | | / \-/ (C)IBM CORP \-/ |
=========|D DALLAS | | | 1981.1983 |
| | 8305 | | | D MALAYSIA |
+--------+============+---------+ +----------8440--AJ-------------+

IBM 5160-087 IBM 5160-078
Q1 1983 Q2 1985
Rev 0 board Rev 1 board
64-256KB cnf 64-256KB cnf

I would like to ask the following questions:

Have you seen any other kind of DIP being used other than the two kinds discussed above (if so, please post the MK number/s as well as you can remember)?
How common do you think the "P-25" variant is?
Were there any other companies producing BIOS chips for IBM?

Based on the post below by Chuck(G), I realized that IBM didn't really mass-produce their own DIP chips in the early 80's. Therefore; Mostek has been assumed as the producer of those chips instead of IBM.

March 12th, 2010, 03:03 PM
I suspect that IBM used whatever they could find. The one in front of me is an MK36887N-4, ZA code, looks to be a Mostek chip, though it doesn't identify itself as such.