The 11/23, 11/23+ and 11/24 all used the same chip set. The actual processor existed as two chips mounted on one carrier. This was the DCF-11 (the 'Fonz') chip. The memory management unit was a second chip and the floating point unit was a third chip (again, actually two chips on one carrier). In addition, there was a CIS (commerical instruction set) chip which was 6 chips on a single carrier (I have a couple of 11/23+ boards with CIS). Megan Gentry Former RT-11 Developer +--------------------------------+-------------------------------------+ | Megan Gentry, EMT/B, PP-ASEL | Internet (work): gentry(a)zk3.dec.com | | Unix Support Engineering Group | (home): mbg(a)world.std.com | | Digital Equipment Corporation | | | 110 Spitbrook Rd. ZK03-2/T43 | URL: http://world.std.com/~mbg/ | | Nashua, NH 03062 | "pdp-11 programmer - some assembler | | (603) 884 1055 | required." - mbg | +--------------------------------+-------------------------------------+