Editing ARM architecture family (section)

===BBC Micro===
{{Main|BBC Micro}}
[[Acorn Computers]]' first widely successful design was the [[BBC Micro]], introduced in December 1981. This was a relatively conventional machine based on the [[MOS Technology 6502]] CPU but ran at roughly double the performance of competing designs like the [[Apple II]] due to its use of faster [[dynamic random-access memory]] (DRAM). Typical DRAM of the era ran at about 2&nbsp;MHz; Acorn arranged a deal with [[Hitachi]] for a supply of faster 4&nbsp;MHz parts.<ref>{{cite web |last=Fairbairn |first=Douglas |date=31 January 2012 |title=Oral History of Sophie Wilson |url=http://archive.computerhistory.org/resources/access/text/2012/06/102746190-05-01-acc.pdf |access-date=2 February 2016 |url-status=live |archive-url=https://web.archive.org/web/20160303221351/http://archive.computerhistory.org/resources/access/text/2012/06/102746190-05-01-acc.pdf |archive-date=3 March 2016 |df=dmy-all}}</ref>

Machines of the era generally shared memory between the processor and the [[framebuffer]], which allowed the processor to quickly update the contents of the screen without having to perform separate [[input/output]] (I/O). As the timing of the video display is exacting, the video hardware had to have priority access to that memory. Due to a quirk of the 6502's design, the CPU left the memory untouched for half of the time. Thus by running the CPU at 1&nbsp;MHz, the video system could read data during those down times, taking up the total 2&nbsp;MHz bandwidth of the RAM. In the BBC Micro, the use of 4&nbsp;MHz RAM allowed the same technique to be used, but running at twice the speed. This allowed it to outperform any similar machine on the market.<ref name="reghardware">{{cite news |last=Smith |first=Tony |date=30 November 2011 |title=The BBC Micro turns 30 |website=The Register Hardware |url=http://www.reghardware.com/2011/11/30/bbc_micro_model_b_30th_anniversary/ |access-date=12 December 2011 |url-status=live |archive-url=https://web.archive.org/web/20111212044749/http://www.reghardware.com/2011/11/30/bbc_micro_model_b_30th_anniversary/ |archive-date=12 December 2011 |df=dmy-all}}</ref>