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32-bit computing
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==Technical history== [[File:XC68020 top p1160084.jpg|thumb|Motorola 68020 prototype from 1984. It features a 32-bit ALU and 32-bit address and data buses.]] The world's first stored-program [[electronic computer]], the [[Manchester Baby]], used a 32-bit architecture in 1948, although it was only a [[proof of concept]] and had little practical capacity. It held only 32 32-bit words of RAM on a [[Williams tube]], and had no addition operation, only subtraction. Memory, as well as other digital [[electronic circuit|circuits]] and wiring, was expensive during the first decades of 32-bit architectures (the 1960s to the 1980s).<ref>{{cite book|last1=Patterson|first1=David|last2=Ditzel|first2=David|title=Readings in Computer Architecture|date=2000|publisher=Academic Press|location=San Diego|isbn=9781558605398|page=136}}</ref> Older 32-bit processor families (or simpler, cheaper variants thereof) could therefore have many compromises and limitations in order to cut costs. This could be a 16-bit [[Arithmetic logic unit|ALU]], for instance, or external (or internal) buses narrower than 32 bits, limiting memory size or demanding more cycles for instruction fetch, execution or write back. Despite this, such processors could be labeled ''32-bit'', since they still had 32-bit registers and instructions able to manipulate 32-bit quantities. For example, the [[IBM System/360 Model 30]] had an 8-bit ALU, 8-bit internal data paths, and an 8-bit path to memory,<ref>{{cite manual|url=http://www.bitsavers.org/pdf/ibm/360/functional_characteristics/GA24-3231-7_360-30_funcChar.pdf|title=IBM System/360 Model 30 Functional Characteristics|pages=8, 9|publisher=IBM|date=August 1971|id=GA24-3231-7}}</ref> and the original [[Motorola 68000]] had a 16-bit data ALU and a 16-bit external data bus, but had 32-bit registers and a 32-bit oriented instruction set. The 68000 design was sometimes referred to as ''16/32-bit''.<ref>{{cite web|title=Motorola 68000 Family Programmer's Reference Manual|url=https://www.nxp.com/docs/en/reference-manual/M68000PRM.pdf|page=1{{hyp}}1|date=1992|access-date=18 January 2022}}</ref> However, the opposite is often true for newer 32-bit designs. For example, the [[Pentium Pro]] processor is a 32-bit machine, with 32-bit registers and instructions that manipulate 32-bit quantities, but the external address bus is 36 bits wide, giving a larger address space than 4 GB, and the external data bus is 64 bits wide, primarily in order to permit a more efficient prefetch of instructions and data.<ref>{{cite journal|last=Gwennap|first=Linley|date=16 February 1995|url=http://www.eecg.toronto.edu/~moshovos/ACA05/read/ppro1.pdf|title=Intel's P6 Uses Decoupled Superscalar Design|journal=[[Microprocessor Report]]|access-date=3 December 2012}}</ref>
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