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In computer science, a memory address is a unique identifier for a memory location at which a CPU or other device can store a piece of data for later retrieval. In modern byte-addressable computers, each address identifies a single byte of storage; data too large to be stored in a single byte may reside in multiple bytes occupying a sequence of consecutive addresses.
Many modern computers support virtual memory, which introduces the notions of virtual and physical addresses. Physical addresses are those the computer's circuitry uses to signal an address to RAM chips; to retrieve some data, its physical address is transmitted from the CPU to the RAM, and the RAM responds with the data. Virtual addresses, on the other hand, are the addresses manipulated by the software running on the computer. When the software requests some data, the computer first translates the data's virtual address into a physical address before being transmitted to the RAM. This translation is invisible to software, and allows the software to operate independently of its location in physical memory, giving the operating system the freedom to allocate and reallocate memory as needed to keep the computer running efficiently.
Very often, when referring to the word size of a modern computer, one is also describing the size of virtual memory addresses on that computer. For instance, a computer said to be "32-bit" usually treats memory addresses as 32-bit integers; a byte-addressable 32-bit computer can address 232 = 4,294,967,296 bytes of memory, or 4 gigabytes. However, older computers often supported memory addresses larger than their word size, or else their memory capacity would have been unreasonably small. For instance, the 8-bit 6502 supported 16-bit addresses, or else it would have been limited to a mere 256 bytes. Similarly, the 16-bit Intel 8086 supported 20-bit addresses, allowing it to access 1 megabyte rather than 64 kilobytes. A byte-addressable 64-bit computer can address 264 bytes (or 16 exabytes) which as of 2005 is considered practically unlimited, being far more than the total amount of RAM ever manufactured.
| "Here are the various used ram memory we have in stock." | ||
| 16mb EDO used Ram Memory | 32mb EDO used Ram Memory | 64mb EDO used Ram Memory |
| 32mb Sdram used Ram Memory | 64mb Sdram used Ram Memory | 128mb Sdram used Ram Memory |
| 256mb Sdram used Ram Memory | 512mb Sdram used Ram Memory | 1gig Sdram used Ram Memory |
| 128mb DDR used Ram Memory | 256mb DDR used Ram Memory | 512mb DDR used Ram Memory |
| 128mb Laptop used Ram Memory | 256mb Laptop used Ram Memory | 512mb Laptop used Ram Memory |
