Memory
- Tags
- comp-arch
Refers to the various storage mechanisms on a computer.
Table 1:
Listing of the main kinds of memory and the average size and read/write rate of it for an average machine in the year 2000. Ordered from fastest to slowest (incidentally also most to least expensive).
| Memory | Size (bytes) | Access Rate (bytes/sec) |
|---|---|---|
| Processor Registers | \( 28 \) | \( 1 \times 10^9 \) |
| Internal Cache | \( 32 \times 10^3 \) | \( 500 \times 10^6 \) |
| External Cache | \( 512 \times 10^3 \) | \( 250 \times 10^6 \) |
| Main Memory | \( 256 \times 10^6 \) | \( 100 \times 10^6 \) |
| Disk Memory | \( 13 \times 10^9 \) | \( 100 \times 10^3 \) |
In the old days processes had direct access to memory. Address 1234 corresponds to a particular byte stored in a particular part of the physical memory. Even in systems after that it was hard to adopt virtual memory because it required altering the entire fetch-execute cycle. In the PDP-10 each process used different registers for each process as a workaround to this problem.