Computer Storage - Memory
 | Two general types of memory:
- Dynamic (RAM = random access memory) - the memory where
programs and data are "processed" by the CPU; a loss of power typically
destroys anything stored in dynamic memory.
- Static (disk, CD-ROM) - where programs and data are "permanently"
stored.
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| Memory is typically organized to support files. Files come in
two general types:
- Programs - relatively permanent, unchanging; contains
instructions for execution by the CPU.
- Data - changing; typically accessed by programs; data files are
usually created, re-created (when data changes), and deleted.
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| Types of dynamic memory found in a computer:
 | DRAM - dynamic RAM, standard computer memory. |
| DIMM (dual inline memory module) and SIMM (single inline
memory module) - the modular circuit board for DRAM. |
| SRAM - static RAM, faster than DRAM, requires more space,
typically used as cache to improve CPU to DRAM access. |
| Cache: temporary storage that holds frequently access data, based
on SRAM. |
| L1 Cache: (L = Level) on the CPU chip, runs at same clock speed as the CPU. |
| L2 Cache: SRAM chip, just outside of the processor, but faster
than DRAM. |
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| Instructions are allocated to the L1/2 cache based on various
algorithms that attempt to improve the overall efficiency of the computer
memory operation. |
| The speed of memory access is dependent is upon the memory bus which is
often shared with
the system (running at much slower speeds than the memory and CPU internal
busses). |
| System (Memory) Bus:
| Carries data (and instructions) to and from various discrete components
(CPU, memory, I/O devices) |
| Has evolved from an original 8- bit to larger busses - 64 bit is most
common. |
| Speed of the bus started at 8MHz and has progressed to much higher speeds
(133+ MHZ). |
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| Other types of chip-based memory:
| ROM (read-only memory) - capable of holding the data when power is
turned off; newer versions can be updated; ROM is most often used for BIOS
programs for booting the computer. |
| Flash RAM - holds memory, tends to be expensive, and limited in
number of rewrites. |
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| Disk Storage:
| Magnetic Disk - most common format for storing long-term data.
Price per megabyte has dropped dramatically over the years. Includes
hard disk (high density, long lived, reliable) and flexible (floppy, Zip)
disks (low density, limited lifespan and durability). |
| Optical Storage - CD-ROM and DVD are most popular. Long
lived, reliable, and durable. Older versions were write once, newer
technologies allow rewrite. |
| Holographic - crystal-based storage, very high density and
reliability, also very small and low power; still in development stages. |
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| I/O Bus:
| Usually refers to the bus interface to/from CPU and various devices
(e.g., graphics, network, audio). |
| PCI (peripheral component interconnect) is most common for modern
personal computers. |
| Data width to most components is 32 bits. |
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| Motherboards and chipsets:
| Various discrete components that handle connections between the various
components such as the CPU, various ports, video, and memory. |
| Tend to be very specific in terms of what the do and do not support. |
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