ITPEC IP April 2020 Question 11

I only — a 64-bit CPU has a larger theoretical memory space; statements II and III are false.

• •I True: 32-bit addresses can distinguish 2³² bytes, 4 GB, while 64-bit addresses allow 2⁶⁴ bytes in theory, about 16 EB.
• •II False: 64-bit PC processors stay compatible with 32-bit software, so a 32-bit OS installs and runs on them; it just cannot use the 64-bit mode or more than about 4 GB of memory.
• •III False: the speed of a USB memory is set by the USB standard (USB 2.0, USB 3.0), the controller and the flash memory itself; the CPU's bit width does not double it.

Answer (a)

Why not others:

• •(b) I, II — adds II, but 32-bit OSs do run on PCs with a 64-bit CPU
• •(c) II, III — both statements are false, and the true statement I is left out
• •(d) III — a transfer speed does not scale with the CPU's bit width, and the true statement I is left out

Key rule: A CPU's bit width is how much data and address it handles at once: it bounds the addressable memory at 2ⁿ bytes, but it does not set the speed of peripherals.

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