View source for MB20 core memory

The '''MB20''' was a [[core memory|core]] [[main memory]] system for the later [[PDP-10]]s, principally the mid-period [[KL10]]. An MB20 contained up to four memory controllers<sup>*</sup>, each with up to four 32KW storage modules, for a maximum of 512KW; [[parity]] is provided to protect the memory contents. The [[access time]] is 1.04 µseconds, and the [[cycle time]] is 1.92 µseconds (both for the first [[word]] in a 4-word block, using four-way [[interleaving]]).

It connected to the KL10's so-called internal memory bus, the S-Bus; controllers 0 and 1 are connected to S-Bus 0, and controllers 2 and 3 to S-Bus 1. For interleaving, each controller is configured as to which addresses (out of the 4 in an S-Bus block) it will respond to; both 2-way and 4-way interleaving require controllers to be set to 'odd' or 'even'. In 4-way interleaving, in addition to two controllers being actuated at the same time, each controller can start two modules reading at the same time.

<nowiki>*</nowiki> - <i>DEC documentation conflicts on this; the 'MB20 Internal Memory Unit Description', EK-MB020-UD-001, December 1976, says optionally four (pg. 1-1) - and has generally been followed for this writeup; the 'DECsystem-10 DECSYSTEM-20 Processor Reference Manual', AA-H391A-TK, July 1980, says two (pg. G-18).</i>

==See also==

* [[MA20 core memory]]

==External links==

* [http://www.bitsavers.org/pdf/dec/pdp10/KL10/EK-MB020-UD-001_Dec76.pdf MB20 Internal Memory Unit Description] (EK-MB020-UD-001)
* [http://www.bitsavers.org/pdf/dec/pdp10/memory/MP00179_MB20_Schematic_Aug76.pdf MB20 Field Maintenance Print Set] (MP00179)

[[Category: PDP-10 Memories]]