BRDB; Assistant Programmer; Exam: 18.03.2023 (BUET)প্রশ্ন ও সমাধান

32-bit vs 64-bit processors differ mainly in the width of the CPU registers/data path, which determines how much memory the CPU can directly address and how much data it processes per instruction.

Aspect	32-bit Processor	64-bit Processor
Register/word size	32 bits	64 bits
Max addressable memory (theoretical)	2^32 = 4 GB	2^64 ~ 18.4 x 10^18 bytes (~16 exabytes)
Practical RAM support	Usually capped at 4 GB (often ~3.2 GB usable)	Effectively far larger — real motherboard/OS limits (commonly up to a few TB) apply well before the theoretical ceiling
Data processed per cycle	32 bits at a time	64 bits at a time — better performance for large computations
OS/software needed	32-bit OS and drivers	64-bit OS (also usually runs 32-bit software, not vice versa)
Typical use today	Legacy/embedded systems	Virtually all modern desktops, laptops, servers

Maximum memory of a 64-bit system: theoretically 2^64 = 18,446,744,073,709,551,616 bytes (about 16 exabytes); in practice, usable RAM is far lower, limited by the CPU's real address-line count, motherboard slots, and OS edition (most consumer 64-bit Windows editions cap out around 128 GB to 2 TB, not the full theoretical maximum).

Exam takeaway: 64-bit doubles the register width over 32-bit, giving a theoretical address space of 2^64 bytes (~16 EB) versus 32-bit's hard 4 GB ceiling — real-world RAM limits come from hardware/OS, not the theoretical CPU maximum.