A+ Hardware Service Technician: System Architecture

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Memory

ROM

ROM (Read-Only Memory) is a form of non-volatile memory. Non-volatile memory keeps its contents even there is no power. Read-only memory is just that, read only, it cannot be written to. The computer ROM contains the setup program and POST (Power On Self Test) software.

RAM

RAM (Random Access Memory) is a volatile type of memory which loses its information when power is not present. RAM is where your software and data is stored when your computer is on and you are actively using or accessing them.

There are many different types of RAM common in today’s PCs, though the different types fit into one of these two categories:

DRAM – Dynamic RAM. Dynamic RAM needs to be refreshed thousands of times a second.

SRAM – Static RAM. Does not need to be refreshed like DRAM, which makes it faster. More expensive than DRAM.

PROM

PROM (Programmable ROM) is a programmable type of ROM. It cannot be erased or changed once it is recorded.

EPROM

Eraseable PROM can be erased using a UV light on a special window on the chip. This chip can be reprogrammed.

EEPROM

Electronically Erased PROM can be erased using a special electrical charge. Chips can then be reprogrammed after erased. Most modern day BIOSs are stored in EEPROM.

VRAM

Video RAM is used on video cards to display video to the monitor. VRAM is dual-ported, it can be read from and written to at the same time from two different devices. VRAM is a very fast type of memory used on most video cards.

WRAM

WRAM (Windows RAM) is a dual-ported type of memory - meaning you can read and write to the RAM at the same time from different devices. It was developed to be an extremely fast graphics RAM. The Windows in Windows RAM is the large "windows", or chunks, of memory that can be written to or read from at a given time.

SGRAM

SGRAM (Synchronous Graphics RAM) is synchronized with the system clock. Unlike WRAM, SGRAM is single-ported. It syncs itself to the system clock and can run at speeds up to 100 MHz. It is a type of DRAM.

RDRAM

RDRAM, or Rambus DRAM, is a type of DRAM developed by Rambus Inc. which allows access to the memory at 800 MHz, breaking the current 100 MHz barrier.

Cache Memory

Cache memory is memory used to cache CPU instructions. L1 is cache memory that is located on the CPU. L2 is cache memory located outside the CPU.

DIP

Dual Inline Package is an older RAM type used in older systems.

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