CODEWITHSUNDEEP
memorycpu-architecture
jefe dile
jefe dile

Reputation: 31

is the address bus indicate the size of the address in ram?

I'm sorry for such simple question but this question borders me. so as exp we have the address bus 20 bits.

Does this imply that the address in ram should have 20 bit as size and if the data bus has 16 bits the value in ram are code 16 bit?

Upvotes: 0

Views: 635

Answers (2)

Some programmer dude
Some programmer dude

Reputation: 409176

On any recent PC-like (micro) computers made the last 45 years or so, the smallest addressable unit in memory have always been the 8-bit byte.

And the the bus sizes doesn't indicate word-size or addressable range. Take for example the venerable Motorola 68000 CPU, which had an external 16-bit data bus and a 24-bit address bus. But internally it was all 32 bits, and instructions could fetch 8-, 16- or 32-bit values from memory, and all of the 32-bit address-space was addressable (even if not all was used).

Later version of the 68k CPU added full external 32-bit busses (with the 68020).

Upvotes: 1

rcgldr
rcgldr

Reputation: 28826

The address bus indicates the size of addressable items, including ram, bios, video ram, any I/O mapped devices, ... . The data bus indicates how many bits can be transferred at a time.

20 bits would be 1 MB of address space. However, an external chip to support extended memory could be used to allow more ram. I recall an embedded device (tape drive from the 1980's) that used an 80186, with a custom extended memory interface to support more than 1MB of ram.

Upvotes: 2

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