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16,384 bits (2 kibibytes) – one page of typed text, [4] RAM capacity of Nintendo Entertainment System: 2 15: 32,768 bits (4 kibibytes) 2 16: 65,536 bits (8 kibibytes) 10 5: 100,000 bits 2 17: 131,072 bits (16 kibibytes) – RAM capacity of the smallest ZX Spectrum. 2 18: 262,144 bits (32 kibibytes) - RAM capacity of Matra Alice 90
The maximum random access memory (RAM) installed in any computer system is limited by hardware, software and economic factors. The hardware may have a limited number of address bus bits, limited by the processor package or design of the system. Some of the address space may be shared between RAM, peripherals, and read-only memory.
Memory bandwidth is the rate at which data can be read from or stored into a semiconductor memory by a processor.Memory bandwidth is usually expressed in units of bytes/second, though this can vary for systems with natural data sizes that are not a multiple of the commonly used 8-bit bytes.
As an example, a 512 MB SDRAM DIMM (which contains 512 MB), might be made of eight or nine SDRAM chips, each containing 512 Mbit of storage, and each one contributing 8 bits to the DIMM's 64- or 72-bit width. A typical 512 Mbit SDRAM chip internally contains four independent 16 MB memory banks. Each bank is an array of 8,192 rows of 16,384 bits ...
DDR5 octuples the maximum DIMM capacity from 64 GB to 512 GB. [8] [3] DDR5 also has higher frequencies than DDR4, up to 8GT/s which translates into 64 GB/s (8 gigatransfers/second × 64-bits/module / 8 bits/byte = 64 GB/s) of bandwidth per DIMM. Rambus announced a working DDR5 dual in-line memory module (DIMM) in September 2017.
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. [7]
(For example, if a computer has 2 GB (1024 3 B) of RAM and a 1 GB page file, the operating system has 3 GB total memory available to it.) When the system runs low on physical memory, it can " swap " portions of RAM to the paging file to make room for new data, as well as to read previously swapped information back into RAM.
With 4 GiB or more of RAM installed, and with RAM occupying a contiguous range of addresses starting at 0, some of the MMIO locations will overlap with RAM addresses. On machines with large amounts of video memory, MMIO locations have been found to occupy as much as 1.8 GB of the 32-bit address space. [12]